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July 23, 2018

Sweet Corn Seed Production: Quick Reference

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Sweet Corn Seed Production: Quick Reference - Organic Seed Alliance

Figure 1. Sweet corn at market harvest stage being evaluated. Seed will be harvested from more mature plants (not evaluated at this stage) and allowed to dry down.

Common Sweet Corn Endosperm Types

Endosperm type Gene Description
Sugary su1 Normal or old fashioned sweet corn, creamy texture, low sugars
Sugary enhancer su1/se1 Increased sugar and tenderness compared to sugary
Supersweet sh2 Very high sugars, hold sugars in the field and on the shelf compared to other types, often less tender

Production

Sweet corn is highly outcrossing and wind pollinated. It is monoecious, possessing separate male (tassels) and female (silks) flowers on single plants. It is a long season crop, requiring up to 120 days for fully mature seed. Warm, dry weather is needed during seed dry down and adequate water supply is important during seed maturation and ear development (after pollination). During pollination, high daytime (80-92°F) and nighttime (65-72°F) are best. Sweet corn likes fertile, well balanced soils. Because sweet corn is highly outcrossing, at least 200 plants should be planted to maintain a population. To maximize pollination, direct seeded in a square with 8-12 inches between plants and 30-40 inches between rows. If growing more than one variety, isolate based on endosperm types (su, se, sh2). If the varieties are of the same endosperm type (e.g., se and se), 650 feet between them is enough. If the varieties have different endosperm types (e.g., su and se), double that to 1300 feet between varieties. Sweet corn seed is ready to harvest when the husks are brown, generally this is about 40 days after the silks emerge. Remove the husks and dry the ears on screens at 70-100°F. Keep good circulation and don’t keep the ears at this high heat beyond drying. Once the seed is fully dry (very hard and cannot be dented with a fingernail), shell it using a hand crank sheller or by hand. Screen and winnow the seed to remove chaff and small and immature seed. Seed dried to 8.0% or less moisture can be stored at 40-60°F and 40%RH or less for 1-3 years.

Selection and Variety Improvement

Traits that can be selected for prior to pollination, such as for germination, vigor, and plant stature will increase the effectiveness of selection. Selections made after pollination, such as for ear qualities such as flavor, row straightness, tip fill, yield, and wrapper leaves and husk quality, will still make progress, but it will be slower than selections made before pollination. This is because pollen from undesirable/unselected plants will have contributed to pollination and fertilization of selected plants. This can be avoided by using a family selection method and remnant seed rather than mass selection (see the following OSA guides: “Introduction to On-farm Organic Plant Breeding” and “How to Breed Sweet Corn for Organic Agriculture”).

Figure 1. Sweet corn at market harvest stage being evaluated. Seed will be harvested from more mature plants (not evaluated at this stage) and allowed to dry down.
Trait Timing
Soil emergence After planting
Seedling vigor After planting
Date of first pollen shed
Date of first emerging silks
Incidence of foliar diseases Throughout season
Incidence of lodging Before pollination
Plant height Before pollination
Tassel color At flowering
Stalk color Before pollination
Husk color Market harvest
Ear height on plant Market harvest
Ear length Market harvest
Ear diameter Market harvest
Ear shape Market harvest
Incidence of corn earworm Market harvest
Date of first ears suitable for fresh eating Market harvest
Date of first mature seed Seed harvest
Endosperm type – flour, flint, dent, popcorn, sweet (su, se, sh2) Market harvest, seed harvest
Kernel color Market harvest, seed harvest
Ear fill Market harvest, seed harvest
Tip fill Market harvest, seed harvest
# rows per ear Market harvest, seed harvest
Straightness of rows Market harvest, seed harvest
Kernel texture Market harvest
Kernel tenderness Market harvest
Kernel flavor Market harvest
Kernel sweetness Market harvest

Disease

Use resistant varieties when available. Practice 3-5 year crop rotations. Maintain adequate levels of Nitrogen and Phosphorus to reduce nutrient stress and improve crop growth. Bury old crop residues that may harbor pathogens. Minimize water stress at flowering. Harvest ears with good wrapper leaves and no or only minimal husk damage. Harvest ears as early and timely as possible to reduce the risk of moldy kernels. Dry ears as quickly as possible to 15% and monitor kernel moisture periodically throughout storage. Clean kernel thoroughly with winnowing and screening before storing. Protect kernels from insects and rodents. Diseases are classified by severity with a class of 1 being the most severe and 3 the least severe.

Disease Type Severity class Favorable
conditions
Black bundle disease
(Acremonium strictum)
Seedborne 3 Post flowering water stress
Southern leaf blight
(Helminthosporium maydis)
Seedborne 3 Warm & humid
Black kernel rot
(Botryodiplodia theobromae)
Seedborne 3 Wet weather just after silking
Goss’s bacterial blight & wilt
(Clavibacter michiganensis subsp. nebraskensis)
Seedborne 3 Continuous corn production; reduced tillage; hot and humid
Anthracnose
(Collettotrichum graminicola)
Seedborne 2 High temperature and extended wet periods
Fusarium diseases
(Fusarium spp.)
Seedborne 3 Warm & dry
Northern corn leaf spot
(Helminthosporium carbonum)
Seedborne 3 Warm & high humidity
Charcoal rot
(Macrophomina phaseolina)
Seedborne 3 Warm (80-85°F) and dry
Maize dwarf mosaic virus (MDMV) Seedborne 3 Proximity to johnsongrass
Seedling blight
(Penicillium spp.)
Seedborne 3 Cool, wet, poorly drained soils
Downy mildew
(Peronosclerospora sorghi)
Seedborne 3 High humidity & moderate temperature
Head smut
(Sporisorium holci-sorghi)
Seedborne 3 Temperature between 70-82°F and low soil moisture
Ear rot; stalk rot; seedling blight
(Stenocarpella macrospora, S. maydis)
Foliar Hot & humid just after silking

This resource was made possible thanks to the Montana Department of Agriculture’s Specialty Crop Block Grant Program. 

Crops: Sweet corn

Publication Categories: How-to Guides

Tags: Seed Production, Seed Quality

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