Climatic Considerations and Risks for Seed Production in the Midwest - Organic Seed Alliance
PUBLICATION DATE: August 30th, 2024
AUTHORS: Michael Lordon and Jared Zystro, Organic Seed Alliance; Julie Dawson, Rue Genger, Marissa Nix, University of Wisconsin Madison; Alice Formiga, eOrganic; Erica Kempter, Nature and Nurture Seeds; Keith Mueller, KC Tomato.
FUNDER: Upper Midwest Collaborative Plant Breeding Network / The Organic Research and Extension Initiative, part of the USDA National Institute of Food and Agriculture. Award number 2020-51300-32176.
Table of Contents
Relationship Between Climate, Geography, and Seed Production
Environmental Management and Mitigation Strategies
Weather Related Risks during Seed Maturation and Harvest
Seed-borne Disease Risks in the Midwest
Future Climate Projections and Potential Impacts on Seed Production
Introduction
The Midwest region of the United States is critical to the nation’s seed supply due to its unique geography and cultural history. It is a large and diverse region with a highly variable climate. Warm summers, accessible fresh water, and fertile soils aid the production of both commodity and specialty seed crops, while unpredictable storms, flooding, and droughts remain challenging. The capacity of growers in the region to produce seeds in the future will be impacted by their ability to adapt to extreme weather events, the spread of pests and diseases, as well as the gradual but significant effects of climate change.
In this report, the geographic boundaries of the Midwest will match the U.S. National Climate Assessment and the USDA Midwest Climate Hub. This delineation includes eight states; Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, and Wisconsin. According to 2020 U.S. census data, the region spans over 500,000 square miles, 13% of which is covered in fresh water, with more than 62 million residents. In 2019, USDA reported 565,600 farms in the region, spanning over 255,000 square miles. About three quarters of the arable land in the region is planted in corn or soybeans each year, though a wide variety of specialty crops are also grown.
Geographic boundaries of the Midwest used in this guide.
Map generated with OpenStreetMap.
This guide will address 1) the effects of climate on pollination, fertilization and seed formation, 2) strategies for managing environmental conditions, and 3) crop selection for seed production. There will also be a description of the climate of the Midwest, and a discussion of seed-borne disease risks that producers in the region experience. The geographical and biological composition of the Midwest leads to countless unique agro-ecosystems, and it would not be feasible to include precise descriptions of all of these distinct environments. However, case studies of on-farm seed production and plant breeding across the region will exemplify five different representative environments. Finally, projections of future climate changes across the region will be included, along with discussion of how those changes can impact seed production.
Relationship between Climate, Geography and Seed Production
Most modern food crops evolved in regions of the world outside the United States. Brassica crops (such as cabbage, kale, and broccoli) originated from the coastal shores of western and southern Europe, many Solanaceae crops (peppers and tomatoes) are from regions throughout Central and South America, and the wild relatives of many Apiaceae crops (such as carrots) can still be found in Afghanistan and Turkey. These crops have traveled long distances over thousands of years and have been adopted into the agricultural production and cuisine of many cultures worldwide. They have also been selected and bred by humans, but in most cases the physiological process of flowering, fertilization, and seed maturation still reflect the climate where they originated. It is helpful to keep this in mind when considering how the environmental conditions support or hinder seed production of different species.
Environmental Influences on Pollination and Fertilization
The length of season and appropriate temperatures for plant growth are critical to achieving a successful crop, but sometimes a crop will appear to be growing fine and not form seeds. There can be a field full of flowers and ample insect activity and still no or low seed set. This can be one of the most frustrating experiences as a seed grower. In many cases the climatic challenges in seed production are due to the lack of environmental conditions necessary for successful pollination and fertilization of the crop species. Temperature, moisture, wind, and insect activity must all be conducive for the successful pollination and fertilization needed to produce quality seed. Environmental conditions vary from year to year, and physiological requirements can be subtle and varied from species to species.
a) Temperature
Temperature is a critical factor for many stages of seed development. Producers must be aware of the typical minimum and maximum temperatures in the local environment as well as approximately when they occur. Extreme cold and freezing temperatures can cause irreparable damage during both spring growth and overwintering. The extent and duration of cold temperatures control the ability of many crop species to transition from vegetative to reproductive growth. Excessively hot conditions during pollination and seed set can affect both pollen viability and the receptivity of plant stigmas. It is important for producers to be familiar with how these growth stages are affected by temperature requirements of seed crops to achieve a high yield of quality seed.
Minimum Temperatures
Many crops require a period of cold temperatures to transition from the vegetative to reproductive growth stage. This phenomenon is referred to as vernalization. The duration and intensity of cold needed to meet vernalization requirements varies widely among crops and even among varieties of the same species. Some crops require a relatively short period of cold and can fully vernalize and produce seed in a single season (such as broccoli and radish), whereas others must be grown through an entire winter season (biennial) to fulfill vernalization requirements. It is critical to understand the vernalization requirements of a chosen seed crop in order to achieve reliable and quality seed production.
For seed crops that can be grown from seed to seed in a single season (spring sowing and fall harvesting) and that require minimal vernalization, it is important not to plant out too early in the spring. This can result in the crop meeting its vernalization requirement before the plants have achieved sufficient growth and are too small to support quality reproductive growth and a good seed set. This can be difficult to judge as seasonal temperatures and environmental conditions naturally fluctuate from year to year. Experience and familiarity with both the local environment and the seed crop are the best guides for mitigating this issue.
Minimum temperatures dictate which winter annual, biennial, and perennial crops can successfully be overwintered in the ground and which must be dug up and protected in a cellar or cold storage. The seed grower must find the balance that allows the crop to acquire enough cold exposure to meet the vernalization requirement without incurring damage from freezing temperatures. This applies to crops both in the field and in storage.
Each crop species, and the varieties within that species, have a minimum temperature, or cold tolerance that they can withstand before the cold will result in permanent damage from which the plant cannot recover. This cold tolerance threshold can also vary from crop to crop based on the amount of moisture in the environment at the onset of cold, the wind velocity, and the duration of the cold period, as well as other factors if the crop is outdoors. The critical factor is whether or not the apical growing point, or crown, is damaged by the cold. If damage occurs, the plant will not be able to recover and will likely die. There are few vegetable seed crops that can be successfully overwintered in the field in most locations in the Midwest. In general, if temperatures below 20°F (-7°C) regularly occur throughout the winter in an area, overwintering many seed crops will be difficult. With these winter temperatures, a different seed crop, cold storage, or the use of protective structures should be considered.
Although the amount of cold required varies by both species and variety, a general rule that applies to most biennials for successful vernalization is for the crop to receive a cumulative time of 45 days at or below 50°F (10°C). If the local environment does not provide enough cold to meet the crop’s needs, then the crop may need to be dug up and stored under refrigeration in order to achieve successful vernalization. If storing the crop under refrigeration or in a cold room of any type, most biennials will require temperatures below 40°F (4°C), with exceptions for bulbing crops like onions. Resources for determining minimum cold tolerance temperatures for specific crops include some gardening books, seed catalogs, and the local Extension service.
Seasonal Fluctuations in Minimum Temperatures
Propensity for, and intensity of, temperature fluctuations in the local environment must be taken into account for seed crops planned to be overwintered. Extreme temperature fluctuations during the winter can be detrimental to overwintered seed crops. Warm periods can encourage the plant to grow, the new growth of which is then vulnerable to damage or death from successive cold periods. Fluctuations in temperature are a challenge for most crops, but some crops that have evolved under conditions of fluctuating temperatures (such as most brassicas and spinach) may be able to tolerate such variable conditions and allow growers to successfully overwinter the seed crop outside in warmer regions of the Midwest. Growers should also be aware of the same phenomenon in early spring when warm periods can be followed by freezing conditions, causing irreparable damage to young plants. To mitigate damage due to these fluctuations, consider using floating row cover or a mulch to minimize temperature variability. There is little information available on which specific crop species are most and least vulnerable to winter (and spring) temperature fluctuations when producing a seed crop. This is due in part to the fact that many of the common winter annual and biennial vegetable crops grown in the U.S. today originated in temperate climates with relatively mild winters and are generally frost-tolerant. Depending on their size, stage of growth, previous exposure to, and duration of, cold, many of these crops will be damaged by temperatures below 29°F (-2°C). Experimentation with a variety of crop species and varieties may be necessary if there is difficulty overwintering a particular seed crop. Variety trials can be very useful for determining which varieties will work in the local environment. Guidance on conducting on-farm trials is available in OSA’s publication: On-farm Variety Trials for Organic Vegetable, Flower, and Herb Producers. Visit www.seedalliance.org to download this free publication.
Diurnal Fluctuations in Temperature
Another temperature consideration is the difference between day and nighttime temperatures in the area, also known as diurnal fluctuation. Does the temperature drop significantly with the setting of the sun? Or is the heat of the day retained throughout the night? Most heat loving crops don’t like cold nights and can incur damage, or fail to set seed, if temperatures dip too low. This is particularly true of the Solanaceae family. They are vulnerable to cold damage if nighttime temperatures are regularly below 50°F (10°C). Tissue damage from cold temperatures above freezing is known as chilling injury. The plant tissues are damaged to the point that they are no longer able to carry on normal metabolic processes even when temperatures rise above freezing.
Lack of seed set in heat loving crops may also result from the fact that pollination and fertilization are challenging under cool nighttime conditions. Pollen may not be produced, or if pollen reaches the female stigma and begins to grow a pollen tube during the day, it may abort and die when nighttime temperatures drop below 50°F (10°C). This can be a challenge for members of the Solanaceae (tomato, eggplant, and peppers), Cucurbitaceae (squash and cucumbers), and Fabaceae (green bean, runner bean, and edamame) crops.
Diurnal fluctuations also affect the overall accumulation of heat units, potentially resulting in slower plant growth and delayed maturation, even with sufficiently high daytime temperatures.
Maximum Temperatures
The timing and intensity of peak heat affects both growth and seed set of crops. Some crops, such as watermelon and eggplant, are heat-loving plants that grow well in high heat conditions. Others, like cauliflower and spinach, grow poorly at high temperatures. There is wide variation in heat sensitivity and preference among crop species and the varieties within them. Consult Knotts Handbook for Vegetable Growers by Donald N. Maynard as a reference for optimum temperature ranges for flowering and seed set. Be sure to take into account the prevailing heat conditions in the local area when deciding which seed crops to grow.
Many crops are most sensitive to heat during flowering and are better able to tolerate heat once the seed is set. For this reason certain seed crops may need to be planted earlier than normal for vegetable production to avoid peak heat during flowering to ensure successful seed set. High temperatures negatively affect pollination and fertilization of nearly all crops. Some crops will produce and release reduced quantities of pollen in response to excessively high temperatures. High temperatures can also desiccate (dry out) pollen, causing it to die, resulting in reduced or non-viable fertilization. These situations can be problematic for cool and warm season crops, such as beets, cauliflower, lettuce, and peas, when daytime temperatures reach or exceed 90°F (32°C) during flowering.
b) Day Length
Day length is a measurement of the number of hours of light and dark in a 24-hour period, which vary seasonally and by latitude. The reproductive cycles of many crops are governed by the amount of light and darkness that they are exposed to in a 24-hour period. This physiological reaction to the length of day and night is called photoperiodism or daylength sensitivity. Flower initiation in crop species affected by photoperiodism is a response to the relative lengths of the light and dark periods, but is generally determined by length of uninterrupted darkness. Many crops have evolved to initiate flowering in response to increased day length in the spring. These crops include cabbage, carrot, onion, and spinach. This evolutionary mechanism allows plants to avoid flowering in the cold of winter when pollinators are not present and weather would prohibit successful seed maturation. Day length sensitivity is variable among crop species and the varieties within them. It is important to know how day length affects a crop and whether the local environmental conditions will be conducive to successful production of quality seed. Crops are generally considered to be “short-day” plants, if they produce flowers when day length is less than 12 hours. Conversely, “long-day” plants flower when day length is greater than 12 hours. “Day-neutral” plants can produce flowers regardless of day length.
Onions are an interesting example of varying sensitivity to day length. Onion varieties are classified as long, short, or intermediate day varieties depending on how many hours of daylight they require for bulb formation, flowering, and seed set. When long day varieties are grown in low latitudes (closer to the equator), they may never flower and set seed because days never get long enough to trigger the biochemical changes that start these processes. If they do manage to flower and set seed in a short day length climate, the timing may be too late to allow for full maturity of the seed before fall. Conversely, if a short day onion is grown in higher latitudes, it may initiate flowering and seed development before the plant has reached full maturity and is able to sustain and support successful seed development. In this case, the plants are too small and immature to produce quality seed. If the plants do manage to set seed, both the seed yield and quality will likely be diminished.
Spinach is another example of a day length sensitive seed crop. The majority of spinach varieties require a minimum of 14 hours of daylight to initiate the transition from vegetative growth into floral development. If spinach is grown for seed in a location that never gets 14 hours of daylight, only a small percentage of plants will likely flower and set seed. However, the seed saved from those plants will result in a more bolt sensitive population. Although this may seem like a good way to produce and retain a new spinach seed source, it is not advised, as a spinach with a propensity toward early bolting will decrease the harvest window and could result in a population that does not grow to full vegetative maturity before transitioning into the floral development and seed production phases. Growing spinach seed crops in northern climates with long days is essential to select for and produce varieties that are not sensitive to early bolting.
c) Frost-Free Days
Frost-free days refers to the total number of days with temperatures conducive to plant growth. Seed crops require a much longer growing season than vegetable crops of the same species, and thus require a strategy for a longer period of management in the field. For instance, a head lettuce crop may mature in 45-65 days, whereas twice that time (120 or more days) is needed to mature a quality lettuce seed crop. Frosts and freezing spells in the fall can prematurely halt the maturation of a seed crop. Conversely, spring frosts can delay initial growth and establishment of the crop, which can throw off the timing of seed production or cause the crop to start setting seed before the plants have reached full vegetative maturity. Therefore, it is important to consider the total estimated length of time required for the crop to reach full maturity to know whether it will be possible to produce a seed crop successfully in an area.
d) Precipitation
Precipitation is the water a crop receives from rain. Precipitation can be both helpful and harmful to the health and success of a seed crop. The timing, duration, and total accumulation of precipitation all affect the crop and need to be factored into and combined with irrigation practices throughout the entire lifecycle of a seed crop. The two most critical stages in crop seed development when precipitation can be most damaging are during flowering and pollination, and final dry down. Both the direct precipitation and the relative humidity it creates can affect the crop.
If it is too rainy during flowering, the activity of pollinating insects may be reduced. Honeybees are especially sensitive to these conditions and will not fly when it is too cool or wet. This is particularly important for cross-pollinated crops that rely on insects for successful pollination. It is also an issue for self-pollinated crops. The pollination of many self-pollinated crops is enhanced by visits from insects who land on and jostle the flowers, encouraging pollen movement within the flower. Rainy and wet conditions can also be detrimental to the pollen movement of cross-pollinated crops that rely on wind for pollen movement. Rain or overhead irrigation can wet the pollen as it is shed by the anthers, either washing it to the ground or rendering it immobile.
Both the amount and the timing of precipitation affect crop growth. As with almost all vegetable crops, most seed crops grow best with watering throughout the season. It is a common misconception that irrigation can be stopped once the seed is set and that this will encourage and facilitate seed maturation. This is not the case. In most climates the crop needs continued irrigation until the seed is fully mature. It is advisable, if possible, to use a drip irrigation system with seed crops, as overhead watering can cause damage and encourage conditions for disease on developing seed pods and heads. Precipitation during seed maturation can increase the incidence of disease both externally and internally if the seed is in some sort of a pod, silique, or covering, and cause disease by directly wetting the seed (which can make it vulnerable to fungal and disease infections). Direct wetting of the seed, whether from irrigation or precipitation, may cause the seed to germinate and sprout on the plant, thus ruining the seed crop. To prevent direct wetting of seeds, it may be necessary to harvest early, cover the crop in the field, or move the crop to a protective structure.
e) Wind
Prevailing wind conditions are an important consideration for seed crop production. Wind is both necessary and helpful for successful pollination, and can be destructive and detrimental during seed maturation and dry down. Timing, direction, and severity of prevailing wind conditions all affect seed production.
Wind is critical for successful pollination of many cross-pollinated crops such as beets, chard, corn, and spinach, all of which rely on air movement to spread their pollen. Full seed set of these crops can be hampered if they experience repeated days of still air or absence of wind during flowering. In this situation the pollen is only able to travel short distances to neighboring plants, rather than being blown throughout the entire field. The result can be a reduced level of pollination and a decreased level of genetic mixing, which are essential for healthy and robust production in cross-pollinating crops. Seed crops grown in a greenhouse can suffer from lack of wind and air movement necessary for pollination of self-pollinated crops. In some self-pollinating plants the anthers (male flower parts) are presented in very close proximity to the stigma (female flower part) so that as soon as the anthers release pollen it falls onto the stigma with little or no prompting or assistance. However, others require some sort of external movement to assist in shaking the pollen loose from the anthers and onto the stigma. For many crops, such as tomatoes, peppers, common beans, and peas, wind movement can facilitate this critical pollen movement within the flowers. Tomatoes being grown for seed in a greenhouse may need to be physically shaken by hand or by using strong fans to introduce a stiff breeze during flowering to ensure good pollination and seed set.
Many seed crops are tall and subject to lodging (falling over) in windy conditions. As plants reach their maximum height in the final stages of seed maturation and dry down, they are susceptible to lodging and their stalks may be weakened. This is something to be particularly aware of if the crop is being taken all the way through full maturity out in the field. Lodging can be especially problematic for lettuce and brassica seed crops that are lightweight when fully dry and vulnerable to being blown about in high wind conditions. The seed pods of brassicas (known as siliques) are vulnerable to cracking open with excessive movement when they are fully dry, which can easily result in crucial seed loss. Tall crops can also be vulnerable to blow down damage if windy conditions prevail during the final stages of seed maturity.
Crop Selection for Seed Production
Dry-Seeded Versus Wet-Seeded Species
Knowing whether a seed crop is dry-seeded or wet-seeded will help determine what climatic factors may be the biggest challenges to producing quality seed. Dry-seeded crops have naked seeds, pods, or capsules that are dry at maturity. Examples of dry seeded crops include grains such as wheat and barley, as well as vegetables such as carrots, fennel, lettuce, chicory, broccoli, cabbage, kale, peas, and beans. Dry-seeded crops require a dry environment (or protective structure) during maturation and harvest. These crops are vulnerable to disease during this time if conditions are wet and cold; and do best in dry, low humidity environments.
Wet-seeded crops have seeds that are embedded in the damp flesh of fruits. There are only two vegetable plant families with wet-seeded fruits: the Solanaceae (including tomatoes and peppers) and the Cucurbitaceae (melons, squashes, and cucumbers). Certain peppers can be treated as dry or wet-seeded crops, as they can be either processed when they are fleshy (wet), or after they have dried (dry). In general the seed of wet-seeded crops is less vulnerable than the seed of dry-seeded crops because it is better protected from disease while it matures inside the fruit. Many of these crops tolerate and sometimes desire higher temperatures and humidity than dry-seeded crops during maturation and harvest.
Seed Crop Climate Categories
Wet- and dry-seeded crops can be further categorized into cool season dry seeded crops; warm season dry-seeded crops; hot season dry-seeded crops; and hot season wet-seeded crops. These delineations further assist in determining which seed crops are most appropriate and most likely successful depending on location.
Cool Season, Dry-Seeded Crops
These crops do best with a fairly long spring season of cool and wet weather and mild temperatures (less than 75°F (24°C)) during flowering and early seed development. Gentle rains and mild winds in the mid-summer followed by dry conditions in the late summer and early fall are ideal for the maturation and harvest of these seed crops. Examples of cool season, dry-seeded crops include spinach, table beets, Swiss chard, turnips, many mustards, Siberian kale, rutabaga, parsnips, and cilantro.
Warm Season, Dry-Seeded Crops
These crops are very similar to the cool season, dry-seeded crops, but prefer slightly warmer and drier spring weather. They also need warmer summer temperatures during flowering (greater than 80°F (27°C)) for optimal pollination and seed set. Warm season, dry-seeded crops need a slightly longer rain-free period for full maturation and harvesting than their cool season counterparts. Examples of warm season, dry-seeded crops include radish, most kales, collards, cabbage, lettuce, peas, and fava beans. Swiss chard and turnips are fairly flexible seed crops that can be produced in both cool and warm season climates, although in general they will both do slightly better in the warmer season climates.
Hot Season, Dry-Seeded Crops
These crops are at their best with warm spring weather and generally require early irrigation. They prefer hot and dry conditions that persist throughout the summer and fall. During flowering and early seed set they like temperatures to rise into the mid 80s°F (27°C) and after flowering they prefer even higher temperatures, into the mid-90s°F, for full seed development and maturation. Examples of hot season, dry-seeded crops include garden beans, dry beans, lima beans, edamame, carrots, onions, and sweet corn.
Hot Season, Wet Seeded Crops
These crops like it hot. They like warm springs and hot summers with warm nighttime temperatures. Warm spring days that average around 65°F (18°C) and hold their warmth into the night help these crops establish strong early growth and realize high-yielding, fully pollinated fruits. High temperatures, in excess of 90°F (32°C), are easily tolerated during flowering and early fruit and seed set of these crops. Moderate to high humidity conditions are also good for the growth of their wet fleshed fruits. They can tolerate somewhat drier conditions and still produce, but might not yield quite as well as they would with a bit of moisture in the air. Crops in this category include summer and winter squashes, cucumbers, melons and watermelons, tomatoes, peppers (hot and sweet types), and eggplants. However, there are always exceptions and it should be noted that cucumbers prefer slightly cooler peak temperatures (less than 80°F (27°C)) and tomatoes prefer slightly hotter peak temperatures (greater than 90°F (32°C)) than described.
Selecting Appropriate Varieties for Location
Different varieties of the same crop vary in their responses to crop stresses. This genetic breadth offers an opportunity to enhance crop growth under environmental, pest, pathogen, and climatic constraints by identifying varieties least affected by the prevailing stress conditions of a particular location. Conducting a variety trial, or series of them depending on the breadth of the needs and interests of the grower, helps determine which varieties are best suited for a particular location.
A variety trial is a scientific experiment in which the hypothesis is that some of the varieties have more desirable characteristics or genetic traits than the others. The goal of the variety trial is to identify the best varieties for a location, market, or production system. As with any scientific experiment, following a rigorous experimental design increases the likelihood that the measured results will be due to the treatment, in this case the variety, rather than from an external influence.
Before seeking out varieties and beginning a trial, it is helpful to create as complete a description as possible of ideal crop characteristics, desired crop traits, and trial goals. This will ensure that seed sourcing, trial planning, and experimental design will result in useful information. Consider the primary challenges in producing seed of the chosen crop and what characteristics and traits will be critical for success. Be sure to take into account the prevailing environmental conditions of the location throughout the entire life cycle of the seed crop to ensure that all vernalization, pollination, seed set, and seed maturation requirements can and will be met. Variety trials require time and attention to produce successful and valuable results.
If a desired variety is found, but some aspects of it are dissatisfying, additional trials of that particular variety can be conducted using as many seed sources as possible. The performance of a variety can be strongly dependent on how well it has been cared for and maintained by a seed company, breeder, or seed producer. The same variety from several seed sources can exhibit widely variable performance and yield. This can be especially true for open-pollinated varieties of cross-pollinated crops, for which genetic drift can occur rapidly if the variety is not carefully selected and maintained. Use descriptions in trusted seed catalogs or suggestions and input from fellow local growers in the area when selecting varieties to include in the trial.
For further information and guidance on conducting a variety trial, please refer to OSA’s On-farm Variety Trials: A Guide for Organic Vegetable, Herb, and Flower Producers. This is available as a free download at www.seedalliance.org.
Environmental Management and Mitigation Strategies
Table 1. Mitigation strategies to address climatic constraints in seed production
| Mitigation Strategy | Low Temperature | High Temperature | Day Length | Frost-Free Days | Precipitation | Wind |
|---|---|---|---|---|---|---|
| Site Selection | X | X | X | X | X | X |
| Variety Selection | X | X | X | X | ||
| Timing of Planting | X | X | X | X | ||
| Shade Cloth | X | |||||
| Greenhouse / High Tunnel | X | X | X | X | ||
| Row Cover | X | X | ||||
| Mulch | X | X | X | |||
| Windbreaks | X | |||||
| Staking | X |
Mitigation Techniques for Temperature
There are three primary ways to manage and mitigate the negative effects of extreme high temperatures on seed crops. First and foremost is to manage the timing of planting, whether direct seeded or transplanted. Planting early (as early as possible, or even overwintering) allows the crop to achieve flowering and pollination before potentially damaging peak heat times. Another option is to use shade cloth or construct a shade structure near or around the crop to protect it from direct heat and create a slightly cooler microclimate. Planting the crop in a known cooler microclimate area in the landscape also helps to minimize heat damage. Conversely, if the local climate is too cool for the seed crop, consider planting into a hoop house, greenhouse, or high tunnel to achieve the temperatures needed for flowering, strong pollination and fertilization, and seed set.
Mitigation Techniques for Day Length
Although producers can extend day length by growing the seed crop under lights in a greenhouse, this is not likely to be an economically feasible option in seed production. Field production of highly day length sensitive crops requires appropriate timing of planting to achieve appropriate vegetative growth prior to the critical day length that will induce flowering in the crop.
Mitigation Techniques for Frost-Free Days
Quality seed crops can still be produced in areas with a short frost-free season, but it may require a combination of season extension tools such as greenhouses, high tunnels, row covers, mulches, and cold storage facilities.
Mitigation Techniques for Precipitation
If too much precipitation is present, the crop may be grown in a high tunnel, greenhouse, or other protective structure and irrigated to control watering. If precipitation is limited, irrigation must be applied to ensure adequate water for healthy plant growth. Again, drip irrigation is generally preferable to overhead irrigation to avoid disease susceptibility and damage caused by wetting plant foliage, flowers, and seed.
Mitigation Techniques for Wind
Negative effects of wind can be mitigated by planting crops in the leeward side of windbreaks in the field and by staking plants to avoid lodging. Fans may be used to increase airflow, facilitating pollination in low-wind environments such as greenhouses. Plants may also be manually shaken gently during pollination to ensure good transfer of pollen from the anthers to stamen.
a) Field Selection
The microenvironment of most farms varies across and between fields. Field selection can significantly influence the environmental conditions for seed crops and careful field selection can help increase or decrease temperatures, wind, moisture, and other field conditions. Choosing warm areas of the landscape can help crops and certain species achieve needed heat units without the addition of protective structures. Consider the prevailing wind conditions and their patterns around the landscape to ensure good pollination and help avoid losses due to crop blow downs during the seed maturation and dry down stages. When dealing with a cool weather seed crop (such as lettuce), choosing shady or cooler microclimates in the landscape can help ensure good seed set and minimize losses due to heat damage.
Most landscapes have variable microclimates based on elements such as orientation toward the sun, protection from wind, and contour of the landscape. Selecting a warm location in the landscape can make a critical difference in the ability of crops to reach seed maturity. Finally, if the local climate is prohibitively cool or has too short a season, the seed crop can be planted in a greenhouse, high tunnel, or other protective structure.
b) Protective Structures
Protective structures can be used to mitigate and manage the effect of a number of climatic influences and impacts. High tunnels and greenhouses provide many of the same benefits for successful seed production. High tunnels are essentially tall hoop-shaped greenhouses and often have sides that can be easily rolled up to facilitate temperature regulation and airflow. These structures can provide substantially increased heat units and growing days to accommodate heat-loving crops and extend the growing season for the seed crop. Seedlings may also be started in a greenhouse to give field planted crops a jump on the season. Planting into one of these structures in early spring can extend the beginning of the growing season, allowing the seed crop to get established earlier than if it was planted outside. A caution here is to think about how long the seed crop will be in such a structure in relation to the value of the seed produced. Generally tunnel and greenhouse space is valuable and only recommended for the full life cycle of a seed crop if the resulting seed is of substantially high value. An exception to this may be overwintering a winter annual or biennial in such a structure when it would other- wise not be used to produce a crop for market.
Greenhouses and high tunnels can be supplemented with additional light and heat to meet seed crop needs. Necessary combinations of additional light and heat may be needed to achieve successful vernalization, pollination, accumulation of heat units (Growing Degree Days) or to bring the crop to full maturity. It may be possible to integrate a seed crop into greenhouse or high tunnel production while maintaining vegetable production in the house at the same time. This can be of great benefit to all crops by encouraging the presence of a diversity of pollinators.
c) Mulches
Seed crops grown in areas that regularly experience extreme cold in the winter may benefit from various mulches to protect them from cold damage in the field. In England, for example, heavy straw mulches are used to assist in overwintering carrots in the field. However, care must be taken to avoid covering the apical growing point of the root. In some cases, even a dry snow layer can provide more insulation for plants than those exposed to the cold. Care must be taken to monitor the condition of the crop under the mulch and ensure there are no unintended negative effects. Potential negative effects to monitor for include increased disease incidence and rodent damage.
d) Row Cover
Floating row covers, such as Remay, may help extend the growing season in climates with short seasons that are challenged to mature seed crops. A floating row cover can be used to protect seedlings after direct seeding or transplanting during cold spring or fall conditions. In addition to providing frost protection, row covers increase the temperature under the cover, encouraging more rapid plant growth. They also provide protection from pest damage.
Seed crops require adequate growing days and the right environmental conditions to complete maturity and reach ideal quality parameters. Annual seed crops (including lettuce and beans) are usually spring planted and harvested in summer or fall. In areas of the Midwest with milder winters, the use of mulch or row cover may allow cold tolerant annuals (including spinach; brassica greens such as arugula, tatsoi, and mustards; peas; and fava beans) to be fall planted and overwintered. This generally results in earlier establishment and earlier maturity than achieved from spring plantings. However, in many cases fall seeded annual seed crops may have more severe fungal disease problems such as downy mildew, Cladosporium leaf spot, and anthracnose in the spring due to the larger crop canopy present while spring conditions are still cool and moist.
Weather-Related Risks During Seed Maturation and Harvest
The presence of inclement weather during maturation and harvest may adversely affect all dry-seeded seed crops. However, seed crops of some botanical families are especially vulnerable if they lack a pod, shell, or fruit to protect the seed from repeated wetting and infection by wind-borne pathogens. The parsley-carrot family (Apiaceae), spinach-beet family (Chenopodiaceae), and the lettuce-sunflower family (Asteraceae) are all particularly vulnerable in this way. Adverse weather-related impacts may include increased incidence of disease on seed and plants, sprouting of seed both pre- and post-harvest, decreased germination rates and decreased longevity of harvested seed. In addition, wet weather may result in harvest difficulties due to plant lodging and inability to drive in wet fields or properly operate harvest equipment.
High humidity and wet conditions present during rainy periods promote the growth of several bacterial and fungal pathogens of seed and other plant tissues. Rainy conditions can also exacerbate the spread of diseases via splashing or wind dispersal of spores. Pathogens can cause significant damage and loss of quality to seed crops by either infesting or infecting harvested seeds or adversely affecting plant growth.
Infected seed results when bacterial or fungal pathogens grow into the seed tissue and feed on the developing seed. Infection with fungal pathogens in particular may damage the seed by: 1) interrupting seed maturation as the pathogen feeds on the developing embryo; 2) physically damaging the seed surface, endosperm, or embryo; and 3) consuming seed reserves. Effects of pathogen infection may include reduced yields, decreased seed vigor, and decreased germination rates and longevity in storage as fungal pathogens continue to feed on the seed post-harvest.
Infested seed has pathogens either present on the surface of the seed or mixed with harvested seed. Pathogens on or in seed may serve as seed-borne inoculum, spreading diseases to the following crops. As some seed-borne diseases are difficult to control and can cause significant crop losses, production of clean, disease-free seed is a quality criterion demanded by much of the seed industry.
Premature Germination/Seed Sprouting
Premature germination (from the initial stages of the embryo imbibing water through to sprouting) is a key concern when there is persistent rain on plants carrying mature seed. Seeds may begin to imbibe water and even fully sprout while still on the plant (referred to as vivipary) or after harvest from the mother plant. This prematurely germinated seed has reduced viability and is usually a complete loss. Familiarity with the relative levels of dormancy of the species or variety being grown for seed can help growers prioritize preventative measures for high risk crops.
Seeds of many species have evolved hormonal, genetic and physical methods to prevent premature germination. Most species naturally develop a state of short-term dormancy to prevent germination prior to or shortly after seed maturation. In many species this dormancy develops as the seed dries on the mother plant. Physical barriers include the restriction of water or oxygen through the outer layers of the seed. The relative balance of plant hormones such as abscisic acid (ABA) and gibberellins (GA) can also prevent germination prior to the development of dormancy. Finally, genetic pathways including Delay of Germination (DOG) genes play roles in dormancy and germination in many species. These dormancy factors and the physiological and environmental triggers that affect them differ by crop species and variety, resulting in varied tendencies toward preharvest sprouting.
Drying Procedures
Seed and plant material may be dried either in the field, in a covered area such as greenhouses or barns, and/or with the assistance of forced air dryers. If the crop is small enough, mature seed stalks or heads may be cut and brought into the sheltered space. Availability of drying space may require planning and prioritization if multiple seed crops require handling at once. If the crop is large and must be mechanically harvested in the field, the harvested seed should also be laid out and covered/protected in the fields. Some crops, such as carrots, are easier to mechanically harvest with a combine while standing, while others such as most brassicas and beans are often windrowed and dried prior to processing with a combine. If the crop is subject to inclement weather, the best measure may be to have harvesting equipment ready and closely monitor crop moisture and weather conditions in order to harvest as soon as weather permits. Windrows in the field may also be protected by covering with geotextile fabric.
Guidelines for Drying Seed Under Cover
Elevate seed from the ground.
Drying racks or tables with a surface made of screen, grated material such as galvanized hardware cloth, or wooden slats are often used to raise seed material off of the ground and increase air circulation.
Spread seed out and stir often.
Seed and plant material should not be stacked more than 3 feet thick and should be turned or rotated frequently in order to ensure even drying throughout the material. As seed dries it should be stirred carefully to minimize shatter.
Use fans to increase air circulation.
Blowing cool air on damp seed heads greatly facilitates drying. Warm air (from heaters) is sometimes used to decrease humidity, but drying too quickly with heat may damage seed and can result in seed shattering. Temperatures above 90° F may damage seed.
Catch shattering seed.
Capture shattered seed by placing a fine screen or cloth under the drying plant material. Fallen seed requires immediate drying as it is more vulnerable to premature sprouting than seed on seed heads.
Drying Equipment
In addition to having covered space for drying seed in the event of wet weather, growers should be prepared with necessary equipment for efficient drying and handling of seed. Equipment useful for small- to medium-scale growers include: Rubbermaid totes, tarps of all sizes, geotextile landscape fabric, window screening, landscaping staples, baling twine, threshing sticks, fans, and drying tables or racks.
Simple drying racks, drying bins, and tables can be constructed on-farm to facilitate drying harvested seed and plant material. Drying bins are available commercially, but may also easily be built on-farm. Bins are basically a large box with a slatted floor for airflow and a fan system which forces air up through the drying material. Multiple varieties can be dried at once by building vertically stacked racks into the box, but care should be given to laying fine screening or fabric on each rack to prevent physical mixing of dropped seed, particularly when drying different varieties of the same species. In addition to drying bins, tables or racks can be made to aid drying in the open air. By framing table tops or racks out of wood and covering the open frame with hardware cloth, durable screening, metal grating, or simply wooden slats, seeds can be laid out on cloths or fine screening and elevated so that air flows below and above the drying seed and plant material.
Midwest Geography and Climate
Geography
Continental
The Midwest, in the interior of the North American continent, is located far from the moderating effects of the oceans, and lacks mountains to the north or south, allowing for incursions of bitterly cold air masses from the Arctic as well as warm and humid air masses from the Gulf of Mexico. The polar jet stream is often located near or over the region during the winter, with frequent storm systems bringing cloudy skies, windy conditions, and precipitation. As the jet stream makes its seasonal retreat northward during the spring and early summer, the combination of sharply contrasting air masses (temperature and moisture) and strong winds aloft often produce outbreaks of severe thunderstorms and tornadoes.
Great Lakes
The Midwest borders four of the five Great Lakes; together, the five Great Lakes contain approximately 21% of the world’s surface freshwater supply. The Great Lakes have a large influence on the local climate, with local near-shore climate conditions created by the temperature differential between the Great Lakes and the land. Near-shore locations are considerably warmer during the winter and cooler during the summer than locations farther away from the shores. A notable feature of the southern and eastern shorelines is the occurrence of “lake effect” snowfall. Water that evaporates from the lakes during outbreaks of cold Arctic air masses is deposited on the downwind shores as snow. Very large snowfall amounts can result. The areas regularly affected by lake effect snowfall have annual average snowfall amounts that are double or more that of non-affected areas. For seed producers, this extra snow can help insulate overwintered crops, but can also delay the start of spring plantings.
Watersheds
A watershed is a land area that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, bays, and the ocean. There are more than 500,000 miles of rivers and streams flowing through the region. More than 40,000 natural lakes and thousands more human-made reservoirs and ponds dot the landscape. Given the scale of agriculture in the Midwest, nutrient runoff can become a significant issue in waterways, especially near outflow points.
In general, water flows out of the Midwest in three possible directions. The majority of the land area of the Midwest region is part of the Mississippi River Basin flowing toward the Gulf of Mexico. This area includes the Ohio, Missouri, and Arkansas River Basins. The Great Lakes Basin includes the entirety of Michigan and areas surrounding the Great Lakes, eventually flowing toward the St. Lawrence river and the Atlantic Ocean. An area of Northern Minnesota is within a watershed that flows north toward Hudson Bay.
Soil
There is considerable variability in soil characteristics across the Midwest Region in terms of drainage, fertility, slope, and structure. In general, much of the prime farmland in the Midwest is relatively flat, with a silt-loam soil that is moderately well drained, fairly rich in organic matter, and with a deep, arable root zone.
For a good understanding of the variability of soil characteristics, refer to the Midwestern Climate Center Soils Atlas and Database. The USDA Natural Resources Conservation Service (NRCS) offers a web-tool for understanding your local soil characteristics. NRCS also manages several programs and initiatives that can provide resources (including financial resources) for managing soil and water health. There are links to these resources available at the end of this report.
Urban Areas
All of the Midwest states, except Illinois, have lower urban populations than the national average, yet 74.3% of the Midwest population still lives in urban areas. As of 2023, the region has 41 cities with at least 100,000 residents, including 5 of the 30 most populated cities in the United States.
Major urban centers in the region include Chicago, Detroit, Minneapolis-St. Paul, St. Louis, Cincinnati, Cleveland, Milwaukee, and Kansas City. These areas, and other urban locations, are more sensitive to some weather and climate events due to the specific characteristics of the urban environment such as building density, land use, urban sprawl, and proximity to the Great Lakes.
Climate
Climate, in a narrow sense, is usually defined as the average weather or, more rigorously, as the average and variability of factors such as temperature, precipitation and wind over a period of time ranging from months to thousands or millions of years. The classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization.
Since industrialization, human activities have dramatically altered atmospheric composition and land cover, with consequential impacts on climate. Human-caused emissions of greenhouse gases have warmed the planet by trapping more outgoing energy. The net increase in energy input warms the surface and the air and increases moisture in the lower atmosphere, resulting in significant changes in Earth system processes. The increase in energy input also fuels increases in the frequency and intensity of extreme weather events such as heatwaves and convective storms.
Human activities cause changes throughout the Earth system. The magnitude, and for some processes the direction, of these changes can vary across regions, including within the US. These changes also occur against a background of substantial natural climate variability.
Temperature
Average Temperatures
The average annual temperature varies by about 20°F across the region from less than 40°F in northern Minnesota to at least 56°F in southern Missouri, Illinois, and Indiana. Seasonally, the greatest range in temperature across the region occurs during winter (December-February).
Average winter temperatures range from around 8°F in northern Minnesota to 35°F along the Ohio River. The typical daily minimum temperature in the Midwest winter is around 28°F in the southern region, and below 0°F in the northwest portion. Extreme low temperatures in Minnesota have been recorded as low as -60°F, while temperatures below -30°F have been recorded in Missouri. Areas near the shores of the Great Lakes are considerably warmer during the winter months than locations further from the shore, a result of the temperature differential between the water and the land.
During the summer, minimum daily temperatures in the central and southern Midwest are usually around 65- 70°F. In northern areas, the summertime minimum temperature is usually closer to 50°F. The maximum daily temperature in the summer is usually between 80-90°F for most of the region. Temperatures can rise above 100°F throughout the region, but only in the southern Midwest does it reach triple digit temperatures for several days every year. Growing degree days (also known as heat units) track the total of average daily temperatures over the growing season. The growing degree day totals across the region range from around 2000 in far northern Michigan and northeastern Minnesota to over 4000 in southern Missouri and Illinois.
In the Midwest, it is common for temperatures to change by as much as 20°F throughout the course of a day. Occasionally, 24 hour temperature swings are greater than 30°F. There are typically several weeks in the spring and the fall when day time temperatures rise above freezing, but nighttime lows regularly drop below freezing.
Day Length
The number of daylight hours varies throughout the year, and also varies along a north-south axis. In far northern areas of the region, there are more than 16 hours of light per day around the Summer solstice, and just above 8 hours per day around the winter solstice. In southern latitudes, the day lengths vary from around 9 to 15 hours per day.
Frost-Free Days
The number of frost free days per year, sometimes referred to as the length of the growing season, varies considerably across the region. The average annual growing season ranges from 225 days in southern Missouri to only 104 days in some areas of Michigan’s Upper Peninsula. Last spring freezes are occurring earlier over most of the Midwest region. For a better understanding of the variation across the region, this interactive map is available: https://mrcc.purdue.edu/freeze/freezedatetool
Table 2. Frost Free Season Length Extremes within the Midwest
| Location | Average Last Spring Frost (< 32°F) | Average First Fall Frost (< 32 °F) | Average Frost Free Days |
|---|---|---|---|
| Iron County, MI | June 1st | September 14th | 104 days |
| Pemiscot County, MO | March 24th | November 5th | 225 days |
Precipitation
Average annual precipitation varies across the region ranging from less than 25 inches in northwest Minnesota to more than 46 inches in southern Missouri and along the Ohio River. This pattern is evident in the winter and spring precipitation distributions. During the summer, however, an axis of heavier rainfall extends from western Missouri northwestward through Iowa to near Minneapolis-St. Paul. Average summer rainfall in this area exceeds 13 inches, with more than 14 inches from north-central Iowa into northern Missouri. In the fall, an area from southern Missouri to southwestern Indiana receives the most precipitation on average, 11 to 12 inches. In the winter, precipitation totals are lowest in the western portions of Minnesota and highest in the Missouri Bootheel with over 12 inches. Spring average precipitation is highest in southern Missouri, Illinois, and Indiana with over 16 inches, but less than 6 inches in northwestern Minnesota.
Annual precipitation increased by 5%–15% across much of the Midwest during 1992–2021 (compared to the 1901–1960 average), although some areas experienced reduced precipitation during summer.
Wind Storms,Thunderstorms, and Tornados
The Midwest is affected by severe thunderstorms with tornadoes, hail, lightning, and strong straight-line winds causing human fatalities and injuries along with property and agricultural damage. Severe thunderstorms in the Midwest are most frequent in spring and summer but occur in fall and winter as well, especially further south. Storms also show a peak during the late afternoon and evening time period but overnight, and even morning, severe weather is not uncommon.The Midwest has a long and deadly history of tornadic storms. Five of the ten deadliest tornadoes in US history, along with some significant tornado outbreaks, have hit the region.
Hail and straight-line wind damage are often associated with large, long-lasting clusters of thunderstorms and showers which can last for hours and track for hundreds of miles. The damage from hail and straight-line winds includes everything from homes and property, to farm buildings and crops, to businesses and municipal structures. A hailstorm that moved across Missouri on April 10, 2001, caused roughly $2 billion in damages.
While the average annual number of tornadoes appears to have remained relatively constant, there is evidence that tornado power has increased, tornado activity is increasing in the fall, and that “Tornado Alley” has shifted eastward. The complexes of thunderstorms that bring substantial precipitation to the central United States during the warm season have become more frequent and longer-lasting over the past two decades.
Snow, Ice, and Hail
The primary difference between frozen precipitation is how the different types grow and the maximum sizes of the individual particles. Snow forms mainly when water vapor turns to ice without going through the liquid stage. Sleet are small ice particles that form from the freezing of liquid water drops, such as raindrops. At ground level, sleet is only common during winter storms when snow melts as it falls and the resulting water refreezes into sleet prior to hitting the ground. Hail is frozen precipitation that can grow to very large sizes through the collection of water that freezes onto the hailstone’s surface.
Average annual snowfall varies from less than 10 inches in the far south to more than 200 inches in the Michigan Upper Peninsula. The areas of greatest annual average snowfall are located on the southern and eastern shores (in the lee) of the Great Lakes. Heavy wet snow or freezing rain (glaze) can cause significant damage to trees and power lines that may take days or in some cases weeks to repair, impacting the ability of agricultural businesses and seed companies to operate. Heavy snow can also damage or collapse roofs and structures.
The frequency of snowstorms (defined as producing 6 inches or more of snow in 24 hours or less) in the Midwest ranges from an average of less than one storm per year in southern Missouri to as many as eight storms per year in the Michigan Upper Peninsula. The highest frequency of snowstorms extends from eastern Minnesota eastward across Wisconsin into northern Lower Michigan, and along the eastern and southern shores of the Great Lakes. In contrast, ice storm (freezing rain) frequency is highest in western Minnesota and Iowa, and in a broad band from central Missouri eastward through Ohio.
Plants and agricultural structures can suffer significant damage from hail, especially with larger hailstones that tend to fall faster. Supercell thunderstorms have sustained updrafts that support large hail formation by repeatedly lifting the hailstones into the very cold air at the top of the thunderstorm cloud where they can accumulate more layers of ice. In general, hail 2 inches (5 cm) or larger in diameter is associated with supercells.
Floods and Excess Rain
Severe storms can produce excessive rain over localized areas. These events can produce flooding along rivers and streams as well as in urban areas where drainage is not adequate. Despite typically being short-lived, these flash flooding events can leave behind significant damage. Excessive rain over a longer time period can occur where several rain systems pass over the same area through days or weeks. These events can cause significant delays in planting and harvesting in the agricultural community, resulting in loss of yield. Heavy rain combined with melting snow and breaking ice on rivers also results major flooding in the spring.
Human modification of the landscape can influence the risk of flooding. Farmers can partially protect their land from floods through conservation practices such as planting trees, changing their crop types, or restoring riparian vegetation. Such measures can help lessen flooding impacts on farmlands as well as downstream areas. Other strategies such as dredging or straightening the river, stabilizing the streambank, constructing a levee, or enhancing drainage may help only the very localized area. Yet these practices may actually increase the intensity of water flow. This can exacerbate flooding downstream and degrade river ecosystems.
Heat Waves and Drought
According to the 2012 National Climate Assessment, there is an average of 7 days over 90°F each year in the northern Midwest, with up to 36 days per year in the southern areas, while the number of days over 100°F range from one every two years in the north up to an average of two per year in the south. The factors that determine the region’s climate, such as lack of a moderating or blocking surface feature like mountains, and warm, moist air masses from the Gulf of Mexico, favor occasional episodes of intense heat that are frequently accompanied by very high humidity. The heat index combines temperature and humidity to calculate how hot it actually feels. As of 2012, the southern Midwest states experience between 6 (Indiana and Iowa) and 18 (Missouri) days per year with a heat index over 95°F. Northern states and states that border the Great Lakes such as Michigan and Ohio experience less than 3 days per year.
Evidence suggests that droughts have become less frequent in the Midwest as the region has become wetter. However, future higher temperatures will likely lead to greater frequencies and magnitudes of agricultural droughts throughout the continental United States as the resulting increases in evapotranspiration outpace projected precipitation increases. Non-irrigated land is particularly vulnerable to droughts, and much of the agricultural land in the Midwest is not irrigated.
Seed-borne Disease Risks in the Midwest
While regional seed production is an important aspect of agricultural system resilience and can be a profitable and satisfying farm enterprise, the Midwest region can be a challenging environment for seed production. The relatively short season limits maturation time, extreme cold, especially in the absence of snow cover, can reduce winter survival of biennial crops, and wet and humid weather can promote disease spread. Seed-borne plant diseases are an obvious concern for seed growers, and seed companies may require seedlots to be tested or, for certain crops, certified to ensure disease incidence is below acceptable thresholds. Many pathogens cannot infect seed tissues and so are not seed-borne, but non-seed-borne diseases should also be considered for their overall impact on crop survival and productivity. The basic principles of plant disease management, outlined below, are useful to create strategies for limiting or eliminating seed-borne and other diseases. Some of these strategies, such as cleaning equipment and managing crop debris, are good general practices, while others will be most effective when applied with a clear understanding of the pathogen life cycle and how it can be disrupted.
Disease Triangle Source: Wikimedia Commons
Development of plant disease requires three elements, sometimes called the “disease triangle” – presence of the pathogen (the disease-causing organism), presence of a susceptible host plant, and an environment that is conducive to plant infection and disease development. For example, if the pathogen is present but your crop has genetic resistance to it, no disease will develop. Similarly, in the case of a pathogen such as late blight that requires an extended period of leaf wetness to infect the crop, if the pathogen is present, your crop is susceptible, but leaves remain dry, no disease will develop.
Plant disease management principles can be broadly categorized as prevention (management strategies applied before plants are infected) and therapy (management strategies applied to cure an infection). In seed production systems, disease management strategies that prevent infection are preferable to curative management strategies which may not be completely effective. Preventive disease management strategies include:
Exclusion – preventing introduction of the pathogen. The primary example of this strategy for seed production is to plant seed stocks certified to be disease-free or to have pathogen incidence below a given threshold. Other examples include preventing the movement of pathogen-contaminated soil and plant debris by cleaning and controlling movement of agricultural equipment and tools.
Eradication – destroying pathogen inoculum. Examples include hot water treatment of seed to kill pathogens, crop rotation and removal of crop debris to break disease cycles, removal of weeds, ornamentals and other plants that host the disease of concern, and control of insect vectors. Consider potential sources of inoculum such as plant stakes, clips, greenhouse benches, and seedling trays, and ensure that these are also sanitized.
Avoidance – selecting a time or place for seed production where the pathogen is not present or the environment does not allow the pathogen to infect the crop. Examples include planting early maturing cultivars to reduce the time that the crop is vulnerable to infection and, for diseases that spread more readily in humid environments, spacing plants further apart to increase air flow.
Protection – physical or chemical barriers between crop and pathogen that prevent infection. Examples include using row covers to exclude insect vectors of disease and copper sprays to limit fungal and bacterial entry into leaves.
Resistance – selecting varieties that have a heritable resistance to the pathogen. It is important to seek current information on resistance, as pathogen populations continue to evolve and sometimes overcome previously effective genetic disease resistance.
When selecting a crop for seed production, consider the seed-borne diseases that can infect it, and how those diseases can be excluded or controlled in your growing environment. Selection of early maturing and disease resistant varieties can be helpful in managing disease, but market demands for specific varieties may limit your ability to choose varieties with these traits. Cultural controls, including careful management of rotations, field hygiene, and crop production environments to exclude, eradicate, and avoid pathogens, are important strategies for successful seed production. If you plan to use protective structures or barriers such as high tunnels or row cover to extend the growing season and protect overwintering crops, consider how they will impact the growing environment and create a more or less conducive environment for disease spread.
Early detection of disease in a seed production field may give you the opportunity to rogue (remove diseased plants and often their neighbors) quickly enough to prevent disease spread. Accurate identification of the disease organism is essential to choosing appropriate methods for disease control, since the mode of disease spread (for example, by wind, rain splash, or insects), the environmental conditions conducive to disease spread, and the plant organs targeted for infection (for example, leaves versus flowers) will vary among pathogens. Most State universities offer plant disease diagnostic services for a fee, and may be able to offer a diagnosis based on photographs. Contact University plant disease diagnosticians or visit clinic websites for guidance on submitting physical samples and taking informative photographs.
If you are producing seed under contract, it’s important to talk with your contract partner early to set clear expectations for stock seed, disease testing and seedlot quality. If your contract partner is providing stock seed, ensure that they provide you with the results from tests for any seed-borne diseases. If you are providing or purchasing stock seed, ask your contract partner if they require you to have it tested for seed-borne diseases. Your contract partner may also require testing for seed-borne diseases on the seedlots you produce. Disease testing on seedlot samples will only give useful results if the sample is truly representative of the whole seedlot – consider how to sample in a way that represents your entire seed production area. If you are concerned about disease in a particular area of the field, you may wish to harvest seed from that area as a separate seedlot for testing purposes, to avoid potentially contaminating the entire seedlot, or to avoid harvesting any seed from that area of the field.
You and your contract partner should also discuss your backup plan for what to do if disease moves into the crop or a seedlot fails testing. Depending on the crop and disease impacts on marketability, you may be able to sell into a produce market. To inform decisions about whether to redirect a crop to a produce market rather than seed, it is important to scout for disease regularly, test to ensure correct disease identification, and understand disease cycles and potential for spread through a crop.
Seed can be treated with hot water, bleach, or other chemicals such as trisodium phosphate, to eradicate some pathogens, whether from stock seed that you intend to plant, or from seedlots you have produced for sale. You should work with your organic certifier and consult your contract partner to ensure that any materials you use for seed treatment are acceptable for organic production. It is important to consult guides to seed treatment and carefully follow the protocol for the appropriate crop to ensure that treatment will not damage seed and is appropriate for the pathogen you are trying to control. Several online guides to hot water seed treatment are available, including one linked at the end of this report.
A wide range of bacterial, fungal, oomycete (fungal-like), viral and viroid pathogens can infect seeds of different plant families. Not all these pathogens can be described in this publication, and climate change may impact the distribution of seed-borne diseases whether due to changes in the severity and incidence of seed-borne diseases already present in the Midwest, migration of pathogens and pathogen vectors into the Midwest, or emergence of new pathogens. Local Extension professionals and plant disease researchers can provide current information on seed-borne diseases of concern in your region. Below, we describe seed-borne diseases that are relatively common in the Midwest, along with climatic considerations and control options. There is also a section at the end of this report with links to learn more about these diseases with photos.
Black Rot of Brassicas
Black rot of brassicas is a bacterial disease caused by Xanthomonas campestris pv. campestris. The pathogen can infect many species of brassicas, including crops, ornamentals and weeds. It survives in or on seeds and in plant debris, and can survive in soil for one to two months depending on conditions. Black rot of brassicas can affect plants at any stage of growth. Early symptoms include yellowing at leaf edges which develops into characteristic wedge-shaped lesions, wider at the leaf edge. Early detection is important for prompt removal of infected plants, and it is important to remove the entire plant, not just symptomatic leaves. As bacteria move into the vascular tissue, blackening of vascular tissue in petioles, stems and roots will be readily visible in cross-section. Cabbage heads and cauliflower curds will show a black rot, while brassica root crops may not show foliar symptoms but will show blackened vascular tissue when stems or roots are cut in cross section.
The disease spreads through water splash, with the bacteria entering through pores at leaf edges called hydathodes and through wounds. It can also be spread over short distances by insects, wind, in aerosols, and by farm equipment and workers. Warm (80 to 95 °F) and moist conditions are most conducive to disease spread, which can be extensive and very damaging. The pathogen can survive for up to two years on buried crop debris, and if cruciferous weeds are present in the field, it can be maintained indefinitely.
Black rot of brassicas requires a multi-pronged control approach. Obtain seed that has been screened for black rot and produce transplants in a soilless or pasteurized mix. Hot water treatment of seed is effective for disease control, but must be performed carefully to avoid damage to seed. Sanitize seed trays and other equipment used in transplant production. Avoid planting brassica crops in fields infested with cruciferous weeds. Scout brassica crops for early disease symptoms and remove infected plants promptly. After touching infected plants, wash your hands well and clean and sanitize tools. Reduce water splash by using plastic or organic mulches and drip irrigation, and avoid working in fields in wet conditions. Remove or plow in crop debris, and allow at least three years between brassica crops in your rotation.
Tomato Bacterial Speck
Bacterial speck of tomato is the most common bacterial disease of tomato, and is caused by Pseudomonas syringae pv. tomato. While it has been detected in weeds, bacterial speck has primarily been reported infecting tomatoes. This disease causes lesions on fruit, leaves, and stems. Unripe fruit is highly susceptible to infection which results in small black specks (1/16 inch in diameter). Specks are initially slightly raised with a distinct margin, surrounded by a darker green zone which is due to delayed ripening around the lesion. As fruit ripens, pitting can occur. Lesions on leaves are dark brown to black, round, often surrounded by a paler ring as they develop, and most visible on the underside of the leaf. Lesions on petioles and stems tend to be more elongated. Lesions on leaves and stems can coalesce in severe infections.
Symptoms of tomato bacterial speck can be very similar to those of bacterial spot, another seed-borne disease described below, but lesions of bacterial speck tend to be smaller. Management practices for these two diseases are very similar. Early blight and Septoria leaf spot, two fungal tomato diseases that are not seed-borne, can be distinguished from bacterial speck by their symptoms. Early blight lesions are generally larger and have concentric rings, giving them a target-like appearance. Septoria causes brown to grey circular lesions on leaves but does not cause lesions on fruit. However, laboratory testing may be needed to definitively distinguish these diseases from bacterial speck or bacterial spot.
Bacterial speck disease develops most readily in lower temperatures (55 to 77 °F) with high moisture levels. The pathogen spreads by water splash and touch (for example, by handling or tool use) and enters plants through wounds and natural openings such as stomata and hydathodes (leaf pores). High velocity rain and hail contribute to higher rates of disease infection.
Buy tested seed, or treat seed with hot water or sodium hypochlorite (bleach), following published methods carefully to avoid damaging seed. Tomato varieties with resistance to bacterial speck are available. Sanitize seed trays and tools used for transplant production. Avoid overhead irrigation, including for transplants where high plant density can facilitate disease spread. Avoid working with plants when they are wet, and wash hands and sanitize tools regularly. Remove any volunteer tomato plants from planting areas and in rotation years, and use a three-year rotation away from tomatoes.
Bacterial Spot of Tomato and Pepper
Bacterial spot of tomato and pepper is caused by one or more of four species of Xanthomonas bacteria, X. hortorum pv. gardneri, X. perforans, X. vesicatoria, and X. euvesicatoria. These species primarily infect tomato (Solanum lycopersicum), cherry tomato (S. lycopersicum var. cerasiforme), currant tomato (S. pimpinellifolium), pepper (Capsicum annuum) and chili peppers (C. frutescens, C. baccatum, C. chinensis, C. pubescens, Tubocapsicum anomalum). Bacterial spot xanthomonads have also been detected in weeds at low levels.
All above-ground parts of the plant are affected. Tomato leaves show dark brown to black lesions that are roughly circular with a yellow halo, up to ⅛ of an inch in diameter, that may coalesce to blight large parts of the leaf. Pepper leaves show small brown circular spots, and diseased pepper leaves often drop, exposing fruit and leading to sunscald. Fruit spots are up to ¼ inch, slightly raised, brown, and scabbed.
Bacterial spot is often introduced on contaminated seeds or transplants. Transplants may not show symptoms until later in the growing season. Bacterial spot of tomato and pepper develops most readily in humid and high rainfall conditions with temperatures of 75 to 86 F. As for bacterial speck (above), the disease spreads by water splash and handling, and enters plants through natural openings and wounds.
Control measures for bacterial spot are similar to those for bacterial speck. Buy tested seed, or treat seed with hot water or sodium hypochlorite (bleach), following published methods carefully to avoid damaging seed. There are no tomato varieties with resistance to bacterial spot, but a number of resistant pepper varieties are available. Sanitize seed trays and tools used for transplant production. Avoid overhead irrigation, including for transplants where high plant density can facilitate disease spread. Avoid working with plants when they are wet, and wash hands and sanitize tools regularly. Remove any volunteer tomato and pepper plants from planting areas and in rotation years, and use a three-year rotation away from tomatoes and peppers.
Squash Mosaic Virus
Squash mosaic virus (SqMV) infects cucurbits including melons, cucumbers, pumpkins, and squash, and can infect some weed species including lambsquarters and goosefoot. The virus is seed-borne in multiple species of squash (Cucurbita moschata, C. pepo, C. maxima, C. mixta) and muskmelon (Cucumis melo). While other viruses affecting cucurbits are spread by aphids, squash mosaic virus is spread by plant-feeding beetles including spotted and striped cucumber beetles and by grasshoppers. Beetles can retain and spread the virus for up to 20 days.
Young seedlings will show chlorotic mottling and distorted leaf shapes. Mature leaves show dark green mosaic, with blistering and hardening of leaves. Fruit is strongly mottled and can be deformed and discolored. Muskmelon fruit may lack netting.
Use of certified virus-free seed is critical for control of this disease. It cannot be eliminated from seed by treatment with hot water or chemical agents. Control of cucumber beetles is also important. Scout crops for symptoms of squash mosaic virus. Plants showing symptoms should be removed (including roots) and destroyed to avoid spread. Viral diseases are difficult to identify from symptoms, and other viral diseases affecting cucurbits are rarely seed-transmitted, so submitting samples to a plant disease diagnostic clinic is recommended for accurate identification.
Tobacco Mosaic Virus
Tobacco mosaic virus (TMV) infects a wide range of plant species from 30 different families. Disease symptoms vary with the plant species, age and genetics of the infected plant, virus strain, and environmental conditions. Symptoms may include mosaic, mottling, chlorosis (yellowing), necrosis (tissue death), leaf curling, and stunting. In tomato, infection can reduce yield, delay fruit ripening, and cause deformation and discoloration of fruit.
Tobacco mosaic virus is primarily transmitted mechanically. This can be by contact between plants, for example when an infected leaf brushes a leaf on a healthy plant, on tools, and even from the hands of workers after smoking cigarettes. The virus can be transmitted in the seed coat and can infect the germinating seedling through wounds. Tobacco mosaic virus particles are extremely stable and can remain infectious for years outside living plant tissue. Dead plant material from infected plants, or soil containing this material, can be a source of inoculum.
Control measures include use of certified virus-free seed. Tobacco mosaic virus can be eliminated from contaminated seed by treatment with trisodium phosphate and diluted bleach. Tomato and tobacco cultivars with resistance to tobacco mosaic virus are available. Sanitation is another important control measure. Regular hand washing limits spread, and tools and seed trays should be sanitized to inactivate the virus, as should stakes, ties, and clips. Dispose of contaminated soil and infected plant residue by burying away from vegetable production areas or burning plant debris – do not compost. Rotate away from host plants to reduce inoculum in plant debris and soil.
Tomato Mosaic Virus
Tomato mosaic virus (ToMV) infects tomatoes and a wide range of other plants, including solanaceous plants such as pepper, petunia, tobacco and potato,and plants from other families including apple, pear, cherry, lambsquarters and pigweed. Symptoms vary depending on the plant species, variety, and age at infection, the viral strain, and environmental conditions including temperature, day length, and light intensity. On tomato, symptoms often include mosaic and mottling of foliage, distortion of foliage including blistering, twisting and pointed leaf tips, deformation and blotching of fruit, including internal browning. As with many other viruses, symptoms are not useful for definitive identification, so it is recommended to submit samples of symptomatic plants to a plant disease diagnostic clinic for testing.
Tomato mosaic virus is transmitted in tomato seeds, where it can be present in the external mucilage, seed coat, and sometimes the endosperm. It is readily spread from plant to plant by contact during transplanting, from soil contaminated with infected plant tissue, by leaf contact, and during field operations such as pruning and trellising.
Use of certified virus-free seed is an important control measure. Tomato mosaic virus can be eliminated from the outside of seed by treatment with trisodium phosphate, and heat treatment of dry seed can be effective to eliminate virus from external and internal parts of seed. Some resistant tomato cultivars are available. Crop rotation can limit presence of infected plant debris in soil. Sanitation by regular hand-washing, disinfection of tools and equipment, and careful disposal of contaminated soil and plant debris are also critical to control of this virus.
Bean Common Mosaic Disease
Bean common mosaic disease is caused by two closely related viruses – bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV). The disease occurs mostly in Phaseolus species, but has also been reported in European yellow lupin (Lupinus luteus), black-eyed pea (Vigna unguiculata), and mung bean (Vigna radiata).
Symptoms of bean common mosaic disease vary depending on the virus present and whether the host plant possesses genetic resistance to the virus. In varieties susceptible to these viruses, symptoms include leaf mosaic, puckering and deformation of leaves, and leaf rolling and curling. Plants infected while young may be stunted. Pods may also be mottled and deformed. Yield can be markedly reduced and crop failure can occur. Symptomless and mild infections can occur, but may still greatly reduce yield.
When plants possessing resistance to bean common mosaic virus are infected with bean common mosaic necrosis virus, small red-brown spots appear on leaves, and necrosis spreads from veins near these spots through the plant, eventually killing it. Some varieties possess recessive genes that confer resistance to both viruses.
These viruses are highly transmissible by seed, with viral particles mostly located in the embryo. They are spread by several species of aphids which may visit the crop only briefly as winged migrating individuals. Aphids can pick up the virus from an infected plant and transmit it to a healthy plant within a minute of feeding, so control of aphid pests is not an effective way to control the disease. Plant to plant contact can also spread the disease.
Many bean varieties possess resistance to one or both viruses that cause bean common mosaic disease. If planting a susceptible variety, ensure you plant certified virus-free seed.
Case Studies
Nature & Nurture Seeds, Erica Kempter and Mike Levine, Ann Arbor, MI
Approximately how many years have you been growing seeds?
12 years commercially, 25 years including home seed saving and breeding
What are the main types of seed crops that you grow?
Tomatoes, peppers, greens, flowers, herbs, corn, amaranth
What specific features of your local climate makes producing high-quality seeds challenging?
The unpredictability of the climate is a major consideration, as well as the humidity. We generally have a short growing season, but it is difficult to predict in any given year when it will start and end. The summer rains and the dew makes growing some dry seeded crops very challenging, and the moisture plus warmth can lead to significant disease pressure.
The cold temperatures in the winter make overwintering crops challenging, especially when we do not have snow cover as insulation. We are far enough away from Lake Michigan not to get significant amounts of lake effect snow, so we often lose the snow cover during stretches of warmer temperatures, only to then get hit with an extreme cold stretch that can kill a crop. Extended periods of cloudy weather in the winter can cause slow growth of biennial crops, which leads to smaller plants that yield fewer seeds.
Growing crops in a hoop house can offer some protection from the winter cold and the fall rains, but it can also get too hot in there during critical times like pollen development, which leads to crop failure. Severe storms and wind can have devastating effects on infrastructure like hoop houses and trellises, in addition to damaging crops and causing power outages. Smoke from wildfires reduces air quality and limits the ability to work sometimes, but it also might be slowing growth of plants by blocking out sunlight.
Are there specific diseases or pests that affect your seed crops which are influenced by climatic factors?
Fungal diseases are a big concern, like anthracnose, septoria, and alternaria, to name a few. There are some other significant diseases that are spread through insects, like mosaic viruses and aster yellows. We have also seen significant increases in deer ticks since we started farming here, which is concerning. It seems like the milder winters might be leading to diseases and pests shifting northwards. For example, we saw downy mildew on our cucurbits for the first time this year, which we typically associate with more southern areas.
Since you started producing seed, have there been any changes to your local climate that has made seed production more challenging?
The climate has been getting more unpredictable. In our first year at our farm, we had a “polar vortex” winter with record breaking cold temperatures, while some winters the ground will barely freeze at all. When we started, snow cover would usually last for the whole winter; now, there is no “usual.”
We’ve had intense heat waves and droughts, but also cool and wet conditions in spring and summer which led to flooding and delayed planting. Fall conditions used to be more reliably dry, even the late summer was drier; now, rain and humidity is more common.
It seems that weather radar and predictions used to be more reliable, especially for temperature forecasts and frost predictions; now, we don’t trust them as much.
Since you started producing seed, have there been any changes to your local climate that have made seed production less challenging?
Not really. The changes are just too unpredictable.
What strategies, techniques, or infrastructure do you utilize to manage these climatic challenges?
We’ve been trying to focus on the things that are more reliable. We have had success the last few years with adding garlic to our catalog, and we have been trying to grow crops and varieties that mature more quickly. We have also relied on other enterprises, such as our organic gardening service, for financial support when seed or breeding projects do not pay for themselves.
The hoop house that we have has been helpful for some crops, though it has its own challenges. We have added fans and screens to increase ventilation and reduce losses to bird pressure, and we have considered heating or shade cloths to mitigate against extreme temperatures, but all of those measures have their own costs.
We also have to take care not to introduce seed-borne diseases to our farm, which may be difficult or impossible to get rid of. We often heat treat seeds in a hot water bath before planting to reduce the chance that we introduce a seed-borne disease.
Finally, we try to maximize the use of our indoor drying spaces with oscillating fans and dehumidifiers, since we cannot rely on our outdoor spaces for drying crops.
KC Tomato, Keith Mueller, Western Missouri
Approximately how many years have you been growing seeds?
30 years
What are the main types of seed crops that you grow?
Tomato and melon.
What specific features of your local climate makes producing high-quality seeds challenging?
High temperatures during pollen production/set and maturation. Dry periods followed by heavy rain. This leads to cracking of fruit in both melon and tomato.
Hail potential is always a threat but so far have escaped serious damage.
Are there specific diseases or pests that affect your seed crops which are influenced by climatic factors?
Leaf spot diseases can be present following periods of high humidity (dew on plants) and/or rains. They can reduce yield. Some diseases may also be seed transmitted but the most common ones are generally not suspected to be seed transmitted.
Spider mite populations can get rather high during dry periods. This tends to be site specific and have noticed some segregating populations having higher infestations. If I have a water source, washing them off mid day, so the plants can dry before night, seems to help. Spinosad application is usually effective.
Since you started producing seed, have there been any changes to your local climate that has made seed production more challenging?
Our zone has seen a shift in the USDA rating (5a->6a or 6b depending on site). It’s not highly reliable due to “false-springs”. But there does seem to be at least a 2-3 week shift in temperature and even precipitation/severe weather events. It makes planting timing key. With breeding populations (early segregating material) it is rather risky to put out plants too early.
Since you started producing seed, have there been any changes to your local climate that have made seed production less challenging?
It seems like it is drier during the peak season of ripeness. That makes it easier to harvest at correct times.
What strategies, techniques, or infrastructure do you utilize to manage these climatic challenges?
For the high temperatures I try to get crops in earlier, specifically before higher night time temperatures start (it is more the diurnal temperature that affects set). Mulch or living mulch helps to lower soil temperature and can help to reduce radiant heat in the microclimate of the plant architecture compared to bare ground.
For the cracking, mulching helps by maintaining consistent moisture in the soil in reducing sudden uptakes of water after dry periods which result in cracking (or bursting). Timing of any possible applications or side dressing of fertilizer can also play a role in cracking. I try to avoid applying any fertilizer after a certain stage in the plant’s growth. Usually I stop when the first fruits reach a certain size or maturity stage (when cell growth switches to cell expansion versus multiplication.
Circadian Organics / Driftless Seed Supply, Dylan and Skye Bruce, Ferryville, WI
Approximately how many years have you been growing seeds?
6 years
What are the main types of seed crops that you grow?
Cucurbits, tomatoes and peppers, brassicas, and to a lesser extent flowers, carrots, and alliums
What specific features of your local climate makes producing high-quality seeds challenging?
Humidity, heat, rain.
Are there specific diseases or pests that affect your seed crops which are influenced by climatic factors?
Wow I mean yes… aren’t all diseases and pests influenced by climatic factors? Most worried about common vector pests, from aphids to cucumber beetles. Diseases we worry about include angular leaf spot, bacterial speck/spot, black rot, and viruses.
Since you started producing seed, have there been any changes to your local climate that has made seed production more challenging?
Unpredictability is the main difficulty. Seems like every year the last and first frosts are either much earlier or later than average, which makes planning difficult. Also the periods of the year that are supposed to be dry (i.e. July, Aug) have had some crazy rainfall in recent years, while we’ve had drought around planting.
Since you started producing seed, have there been any changes to your local climate that have made seed production less challenging?
Last year was a dry year, which was nice for seed, but we’ve also had very wet years recently. We seem to have a longer season than when I started, which is helpful, even if also scary.
What strategies, techniques, or infrastructure do you utilize to manage these climatic challenges?
Planting timing, planting on raised beds, keeping soil covered with synthetic or organic mulch, growing in cat tunnels (hopefully hoop houses someday), and choosing disease resistant varieties
Cody Egan / Driftless Seed Supply, SE Minnesota
Approximately how many years have you been growing seeds?
7 years fulltime, 10+ all together
What are the main types of seed crops that you grow?
Peppers, Tomatoes, Flowers
What specific features of your local climate makes producing high-quality seeds challenging?
What once were typical benchmarks for the growing season no longer apply. It seems like every year there’s more unpredictability in last and first frost dates, when and how much rain will fall, when the highest temperatures of summer will be. For me these all add up to an increased need for more and more climate mitigating inputs — black plastic, row cover, covered tunnel space.
In the Driftless we also have these beautiful rolling hills, great for isolations, but on the shoulder seasons the differences in lows between a ridge top and a valley bottom can vary greatly — so where a gentle frost might hit some places others it is a decent freeze.
Are there specific diseases or pests that affect your seed crops which are influenced by climatic factors?
Black rot in brassicas, viruses in squash and the whole range of solanaceous diseases. Every year there are new diseases and pests to consider — another troubling factor for seed keepers and farmers/gardeners. I’m worried about how the changing climate will introduce pests that are less commonly found in my area — bean weevils and squash borers to name two. It is hard to get ahead of pest control when the environmental factors that different pests (and diseases) favor keep changing year to year.
During the drought of 2023 (and other dry years), I also saw increased animal pest pressure — deer, rodents and birds looking for something green and wet to munch on. I lost an entire pea seed crop to deer and birds eating basically every pod.
Since you started producing seed, have there been any changes to your local climate that has made seed production more challenging?
Like I said above, just an increased unpredictability in the climatic norms. Even as I sit here on March 3 it is 70+ degrees outside, what will the ramifications for the upcoming growing season be? The increased number of these intense and novel heat events during the growing season mean risking reduced yields or sterile pollen, blossom drop or just general plant stress.
Anecdotally, it also seems like our springs are much windier with greater gusts, not only does this take a toll on infrastructure (high tunnels, bed prep) and the loss of topsoil, but we see a lot more chemical drift from the industrial farms that surround us.
Since you started producing seed, have there been any changes to your local climate that have made seed production less challenging?
It feels like our falls are becoming hotter and dryer. This has made late season seed finishing much better. Last season (2023) we were in a severe drought, it really created a very low disease load but came at a reduction in yield and more time spent watering.
What strategies, techniques, or infrastructure do you utilize to manage these climatic challenges?
For me, managing climate challenges has meant an increased need for more and more chaos mitigating inputs — black plastic, row cover, covered tunnel space. I think mitigating is also doing a lot of work here as well; we can try to implement these strategies and sometimes they are successful and then high winds/derechos blow off greenhouse plastic and leveled tunnels, row cover blows away or isn’t thick enough to stop frost damage. Landscape fabric or black plastic locks in moisture after inches of rain and high humidity. And ultimately almost every option is born of a continued reliance on plastic, which makes them highly unsustainable.
I’ve been pondering, growing and selecting for plants that have high tolerance thresholds. Grower and selection networks that look for reliable varieties that are continuing to adapt to regional climate chaos.
Trouvaille Farm, Lindsay Klaunig, Athens, OH
Approximately how many years have you been growing seeds?
6 years commercially, 10 before that for self/sharing.
What are the main types of seed crops that you grow?
Typically 20-40 varieties per year. Cucurbits, tomatoes, peppers, flowers, beans, etc.
What specific features of your local climate makes producing high-quality seeds challenging?
Wide temp swings in spring (due to our climate and varied topography- all ridge and hollow) make early establishment hit-or-miss. It is hard because seed crops need a longer season than market crops, so we’re usually trying to get in as early as possible.
Summer and fall can be hot, humid and rainy – difficult for dry seeds and a tendency for vining crop disease. Extreme heat sometimes causes pollination issues. Pepper crops often don’t set fruit during July heat (flowers drop) which makes maturing seed tight (especially aji and other longer season varieties).
We have been having increasingly intense rain events – less frequent rain but several inches in a few hours. This is hard on all crops, plants get beat up and drop flowers. Also causes erosion, we grow on ridge tops and terraces.
We often get a push of gulf weather that bumps just barely up to our area in September that brings big wind and rain. It can knock out tall crops right at ripening stage. We have to do a lot of harvesting whole plant a little early and drag under cover, hoping for some post-ripening.
Winters can be wet too, which is difficult for overwintering biennials if they have a tendency to rot. Temps vary a lot, last winter we had a 60°F drop in a few hours, which was hard on all plants and animals.
I spend a lot of time telling myself and others this is a great place to grow seed anyway 🙂
Are there specific diseases or pests that affect your seed crops which are influenced by climatic factors?
I believe we get some airborne disease from the gulf winds that come up. I can’t confirm this – neighbors told me. Our weather would typically come from west in summer, and southeast in winter. But now we have new patterns which might bring new diseases? Not sure if it works like that. But new wind directions do make it harder to plan windbreaks for crops and animals.
Milder winters seem to lead to more pest survival, like cucumber beetles and harlequin bugs. Again, can’t confirm that. I haven’t lived in this one spot long enough to have a good sense. This year the cuke beetles were out well before I had even seeded cucurbits; that’s the earliest I’ve seen.
Erratic spring temps lead to confusing timing for when pests first show up and how many rounds/generations we’ll have. My neighbors told me their guidelines when we first moved here (6 yrs ago) and they don’t work anymore. For example, plant beans after summer solstice to avoid bean beetles. Now they come earlier and have more generations.
Wet and dry periods in the fall affect powdery mildew and downy mildew in cucurbit and other seed crops. With such different weather year to year, it’s trickier to select for resilience to a specific disease or pest that is considered ‘common in our area’.
Since you started producing seed, have there been any changes to your local climate that has made seed production more challenging?
Spoke to that above some. Yes – over past 6 years, we’ve had 3 where longtime neighbors said ‘it never gets this hot (or this dry) for this long’. Big wind and big rain are noticeably more severe. Wildfire smoke is new, and was frequent last year.
Since you started producing seed, have there been any changes to your local climate that have made seed production less challenging?
Bright side of a dry fall – flower seeds looked great, a lot of crops dried in the field without having to be pulled into the high tunnel to finish ripening or drying, which saved labor. Hard to take advantage of this kind of perk since it’s so unpredictable – but luckily I had planted a lot of flowers for other reasons and harvested and sold a lot of flower seed to make up for low yields on some contract crops.
What strategies, techniques, or infrastructure do you utilize to manage these climatic challenges?
Seed crops in a high tunnel to have steadier spring temps and protect from intense rain events. High tunnel also protects from big rain and allows me to grow lettuce for seed and other varieties that wouldn’t otherwise do well with our rainy fall.
Starting to use more shade cloth for rows and will get a big piece for the high tunnel this year. Use a lot of row cover to smooth out temp extremes and exclude pests.
Everything is on drip tape and able to be irrigated with city water. We have to use city water because our ground water is contaminated by gas well fracking. But city water has its own contamination problems, and affects our livestock and plants. Plans this year to set up way more rain water catchment.
Overall, a lot more plastic than I’d like.
Deep mulching when we can, to conserve water and manage soil temp. Trying paper mulch this year.
Fastidious cover cropping in summer (previously mostly just winter) to keep soil covered during big rain.
I’m more careful with which varieties I’ll agree to grow on contract. Must have some resistance or resilience for our pressures.
Generally, just grow a lot of different things and hope something will benefit from whatever kind of weather we get that year. It’s inefficient, but helps us not lose our ass each year.
More careful with hiring. Unfortunately with high heat and wildfire smoke, we have to screen for folks that can handle that and take responsibility for their own safety. We’re running on a tighter margin than ever with time, money, margin of error, and can’t take risks on less experienced helpers.
North Circle Seeds, Zachary Paige, Northwest Minnesota
Approximately how many years have you been growing seeds?
12 years
What are the main types of seed crops that you grow?
A full range of vegetables for small vegetable farms. Lots of solanaceous crops – peppers, tomatoes, eggplant, ground cherries; corn; brassicas; melons; squash and other cucurbits; and more recently a lot of flowers. Not as many beans and greens, but other members of the North Circle collective grow those.
What specific features of your local climate makes producing high-quality seeds challenging?
Overall the climate is good for seed production, with dry falls that help with dry-seeded crops, but we have a short growing season. In recent years, early summer heat has made it challenging to produce some crops. Due to the short season, spinach needs to be planted early for seed production, but once the heat comes it bolts too fast to produce high quality seed. I don’t grow spinach for seed anymore. I had a similar experience with cauliflower in 2022 when hot weather in early summer when the crop was about a month old triggered it to not produce heads. It’s more difficult to predict when to plant garlic in the fall. It should be six weeks before a hard frost but that is later than it was.
Are there specific diseases or pests that affect your seed crops which are influenced by climatic factors?
In 2021, blister beetles caused a lot of damage to a kale seed crop, feeding on the flowers of the stecklings. They went from a few beetles to hundreds over a few days. The next year I saw a few blister beetles but by 2023 I didn’t see any on a seed cabbage crop in a nearby location.
Since you started producing seed, have there been any changes to your local climate that has made seed production more challenging?
Spring heat is more of a problem and has caused me to stop growing spinach seed. It also stresses other crops like corn and brassicas, so I rely more on irrigation. The planting window for crops like corn is narrower since if you miss the early window, it’s too hot and they won’t do well.
Snow cover comes later, which impacts garlic survival. I mulch the garlic but used to see snow cover in October; now there may be no snow cover till January, with several freeze-thaw cycles in late fall and early winter. I’ve started growing ginseng and the lack of snow cover is also an issue for that crop, especially since mice are more active and take bites out of the rhizomes.
Since you started producing seed, have there been any changes to your local climate that have made seed production less challenging?
Longer, warmer falls make it easier to harvest dry-seeded crops like lettuce and carrot. It’s also easier to get long season crops through to full maturity.
What strategies, techniques, or infrastructure do you utilize to manage these climatic challenges?
I produce tomatoes in a high tunnel to extend the season. I grow a lot of long season peppers including Mexican varieties and cover them with Reemay (row cover fabric) to control pollination. This also extends the season, sometimes by a few weeks, which helps with seed production for those late varieties.
I can’t do much about the heat, but use drip irrigation on many crops.
I stagger the planting time for garlic over a bigger window of time to deal with the uncertain frost date.
Future Climate Projections and Potential Impacts on Seed Production
Earth’s climate is changing because humans are increasing the concentrations of greenhouse gases in the atmosphere by burning fossil fuels and through other activities. The increase in greenhouse gases is warming the planet and driving other observed climate trends, including increases in the frequency and severity of many types of extreme weather events. Future changes and impacts depend largely on the choices humans make about future greenhouse gas emissions.
As a result of increases in the atmospheric concentrations of these heat-trapping gases, the planet is on average about 2°F (1.1°C) warmer than it was in the late 1800s. This warming has been accompanied by several large-scale changes: increases in atmospheric humidity; shifting rainfall patterns and more frequent heavy precipitation; seasonal shifts including shorter winters and earlier spring and summer seasons; and changes in the biosphere (such as land and ocean species shifting poleward), among others.
Weeds, insects, and diseases already have large negative impacts on our natural resources (agricultural lands/livestock, forests, recreational areas) and human health. There is mounting evidence that climate change will exacerbate these negative impacts. Ongoing increases in temperature and changes in precipitation patterns will induce new conditions that will affect insect populations, incidence of pathogens, and the geographic distribution of insects, weeds and diseases.
The effects of climate change on the regional potential to produce high quality seeds are complex, and difficult to summarize in general terms. This report should provide an overview of the most critical aspects of climate and geography that influence the viability of seed production, and highlights some of the practical techniques that seed producers can employ to mitigate the environmental challenges that are common in this region.
References and Resources
Sections of this report have been excerpted and/or updated from previous OSA publications and U.S. National Climate Assessments:
Climatic Considerations for Seed Crops: Guidelines and Field Trainings for Organic and Specialty Vegetable Seed Producers https://seedalliance.org/publications/climatic-considerations-for-seed-crops-guidelines-and-field-trainings-for-organic-and-specialty-vegetable-seed-producers/
Weather-Related Risk Reduction Guidelines for Dry-Seeded Specialty Seed Crops https://seedalliance.org/publications/weather-related-risk-reduction-guidelines-dry-seeded-specialty-seed-crops/
Fifth National Climate Assessment, 2023 https://nca2023.globalchange.gov/
Fourth National Climate Assessment, 2018 https://nca2018.globalchange.gov/
Third National Climate Assessment, 2014 https://nca2014.globalchange.gov/
Seed Production Resources
- Buttala L., J. Zystro, M. Colley S. and Siegel. 2015. The Seed Garden. Seed Savers Exchange.
- Colley, M., J. Navazio and L. DiPietro. 2010. A Seed Saving Guide for Gardeners and Farmers (Online). Available at https://seedalliance.org/publications/seed-saving-guide-gardeners-farmers/
- Hagan, K., J. Zystro. 2019 Midwest regional climate considerations for seed production presentation. Available at https://seedalliance.org/publications/upper-midwest-seed-summit-2019-regional-climate-considerations-for-seed-production/
- Healy, K. 2021. Midwest Seed Production Demonstration Report (Online). Available at https://seedalliance.org/publications/midwest-seed-production-demonstration-report/
- Maynard, D.N. and G.J. Hockmuth. 1997. Knott’s Handbook for Vegetable Growers. Wiley and Sons. New York.
- Navazio, J., 2012. The Organic Seed Grower: A farmer’s guide to vegetable seed production. Chelsea Green Publishing.
- Practical Training for On-Farm and Collaborative Plant Breeding Webinar Series. Available at https://seedalliance.org/publications/practical-training-on-farm-ppb-webinars/
- Publications from Organic Seed Alliance website. Available at https://seedalliance.org/all-publications/
Midwest Climate and Geography Resources
- USDA Midwest Climate Hub https://www.climatehubs.usda.gov/hubs/midwest
- Wisconsin Initiative on Climate Change Impacts https://wicci.wisc.edu/
- University of Minnesota Climate Adaptation Partnership https://climate.umn.edu/
- Drought monitoring:https://droughtmonitor.unl.edu/CurrentMap.aspx
- Midwest Climate Collaborative https://midwestclimatecollaborative.wustl.edu/
- North Central Climate Collaborative https://northcentralclimate.org/
- MVEG climate change working group https://www.mvegnetwork.org/connect
- Pests and Diseases https://www.climatehubs.usda.gov/taxonomy/term/400
- Warner, B. P., R. E. Schattman, & C. Hatch. 2017. Farming the floodplain: Ecological and agricultural tradeoffs and opportunities in river and stream governance in New England’s changing climate. Available at https://www.climatehubs.usda.gov/sites/default/files/FarmingtheFloodplain_508.pdf
- Interactive Freeze Date Tool https://mrcc.purdue.edu/freeze/freezedatetool
- NOAA Solar Calculator https://gml.noaa.gov/grad/solcalc/
- Midwestern Climate Center Soils Atlas and Database https://www.isws.illinois.edu/pubdoc/C/ISWSC-179.pdf
- USDA NRCS Web Soil Survey https://websoilsurvey.nrcs.usda.gov/app/
- Soil Geography Maps and Datasets https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soils/soil-geography
- USGS Watershed Map https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/thumbnails/image/watershed_map.png
- What is a watershed? https://oceanservice.noaa.gov/facts/watershed.html
- Daylength Data https://aa.usno.navy.mil/faq/longest_day
- USDA National Agricultural Statistics Service, Number of Farms and Land in Farms, 2019 https://www.nass.usda.gov/Publications/Todays_Reports/reports/fnlo0220.pdf
Seed-Borne Disease Resources
- Bacterial Speck of Tomato https://ag.umass.edu/vegetable/fact-sheets/tomato-bacterial-speck
- Bacterial Speck of Tomato https://extension.msstate.edu/publications/bacterial-speck-and-bacterial-spot-tomatoes
- Bacterial Spot of Tomato and Pepper https://content.ces.ncsu.edu/bacterial-spot-of-pepper-and-tomato
- Bacterial Spot of Tomato and Pepper https://extension.umn.edu/disease-management/bacterial-spot-tomato-and-pepper
- Bean Viruses https://ipm.cahnr.uconn.edu/bean-viruses/
- Brassica Black Rot https://extension.umn.edu/disease-management/organic-management-black-rot
- Brassica Black Rot https://ipm.cahnr.uconn.edu/black-rot-of-crucifers
- Brassica Black Rot https://ag.umass.edu/vegetable/fact-sheets/brassicas-black-rot
- Brassica Black Rot https://content.ces.ncsu.edu/black-rot-of-brassicas
- Cucurbit Viruses https://extension.umn.edu/disease-management/cucurbit-viruses
- Cucurbit Viruses https://www.vegetables.cornell.edu/pest-management/disease-factsheets/virus-diseases-of-cucurbits/
- Hot-Water Seed Treatment Guide https://smallfarms.oregonstate.edu/sites/agscid7/files/blackleg_rule_hot_water_treatment_2017-02-18.pdf
- Tobacco Mosaic Virus https://www.apsnet.org/edcenter/disandpath/viral/pdlessons/Pages/TobaccoMosaic.aspx
- Tomato Viruses https://ipm.cahnr.uconn.edu/mosaic-diseases-of-tomatoes
- Tomato Mosaic Virus https://blogs.ifas.ufl.edu/stlucieco/2023/03/03/tomato-mosaic-virus-tomv-and-its-management/
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