One of the most important management decisions a corn grower makes each year is the selection of corn hybrids for spring planting. During the past 40 years there has been continuous improvement in the genetics of corn hybrids which has contributed to steady increases in grain yield potential ranging from 0.7 to 2.6% per year. To stay competitive growers must introduce new hybrids to their acreage on a regular basis.
Growers should choose hybrids best suited to their farm operation. Corn acreage, soil type, tillage practices, desired harvest moisture, and pest problems determine needs for such traits as drydown, disease resistance, early plant vigor, plant height, etc. End uses of corn should also be considered - is corn to be used for grain or silage? Is it to be sold directly to the elevator as shelled grain or used on the farm? Capacity to harvest, dry and store grain also need consideration. The following are guidelines to use in choosing hybrids that are best suited to various production systems.
Corn for grain should reach physiological maturity or "black layer" (maximum kernel dry weight) one to two weeks before the first killing frost in the fall. Use days-to-maturity and growing degree day (GDD) ratings along with grain moisture data from performance trials to determine differences in hybrid maturity. Late hybrids will not always mature or dry down adequately before frost, resulting in wet grain or silage. Although full season hybrids usually out yield short season hybrids, in recent years early maturing hybrids have been developed with yield potential approaching those of full season types. When confronted with delayed planting or replanting decisions, switch to early to medium maturity hybrids adapted to your area, but avoid short season hybrids which are earlier than those normally used in your area.
This trait is particularly important in areas where stalk rots are perennial problems, or where field drying is anticipated. If you have your own drying facilities and are prepared to harvest at relatively high moisture levels (>25%), then standability and fast drydown rates may be somewhat less critical as selection criteria. There are some hybrids that have outstanding yield potential but are prone to lodging problems under certain environmental conditions after they reach harvest maturity. Traits associated with improved hybrid standability include resistance to stalk rot and leaf blights, genetic stalk strength (a thick stalk rind), short plant height and ear placement, and high "staygreen" potential. Staygreen refers to a hybrid's potential to stay healthy late into the growing season after reaching maturity.
Obtain information from your seed dealer about hybrid reactions to specific diseases that have given you problems or that have occurred locally.
MAJOR CORN DISEASES IN OHIO
Stalk Rots Leaf Blights
- Anthracnose - Northern Corn Leaf
- Gibberella - Gray Leaf Spot
- Fusarium - Bacterial (Stewart's)
Ear/Kernel Rots Virus Diseases
- Gibberella (mycotoxins) - Maize Dwarf Mosaic
(MDM)
- Diplodia - Maize Clorotic Dwarf
(MCD)
This reduces damage from diseases and environmental stress at different growth stages (i.e. improve the odds of successful pollination) and spreads out harvest time and workload. Consider spreading hybrid maturity selections between early-, mid-, and full season hybrids, e.g. a 25-50-25 maturity planting, with 25% in early- to mid season, 50% in mid- to full season, and 25% in full season. Planting a full season hybrid first, then alternately planting early-season and mid-season hybrids allows the grower to take full advantage of the maturity ranges and gives the late season hybrids the benefit of the maximum heat unit accumulation.
Planting a range of hybrid maturities is probably the simplest and most effective way to diversify hybrid genetics. Another way to ensure greater diversity is to purchase seed from one company because seed companies are unlikely to handle genetically identical hybrids in their lineup. However, do NOT sacrifice hybrid performance in order to ensure genetic diversity.
Consider small or irregular seed sizes for plateless planters to reduce costs. Corn hybrids vary genetically in their ability to germinate and grow rapidly under cool stressful conditions, but differences in seed vigor among lots of genetically identical hybrids can be greater than genetic differences. Since seed vigor is influenced by drying, handling, etc., a company's quality control standards for seed conditioning are an important consideration.
Tall, leafy field hybrids with good yield potential are usually good choices for silage. Although differences in feed quality associated with grain protein and silage digestibility do exist among hybrids, these quality differences are usually small and the yield differences among comparative hybrids are much greater. Do not sacrifice hybrid yield performance for marginal differences in quality. If corn hybrids are to be used exclusively for silage they can be up to ten days later in maturity than the standard grain hybrids.
Livestock feeders may want to utilize grain compositional information in selecting hybrids to plant for feed use. For grain used for feed, protein will be of primary interest, for processing uses, oil and starch content will be of importance. As with other hybrid traits, grain protein, oil, and starch levels are highly influenced by the environment in which the hybrid grows. Hence, a hybrid should only be considered if it has shown a relatively high level of one of these attributes over many locations.
Generally it does not pay to compromise overall hybrid performance in order to obtain a slightly higher level of protein, oil, or starch. Keep in mind that the protein percentage data reported for grain are usually measures of crude protein and do not give an accurate indication of feed value if feed rations are balanced on individual amino acids rather than crude protein content.
Evaluate results of state, company, and county performance trials. Because weather conditions are unpredictable, the most reliable way to select superior hybrids is to consider performance last year and this year over a wide range of locations and climatic conditions. When using state performance trials results, two years of data from several locations is usually adequate; test summaries for three or more years may exclude newer genetics with better performance potential.
On-farm strip tests should not be relied on heavily in hybrid selection because they cannot predict hybrid performance across a range of environmental conditions. However, on-farm hybrid tests can be useful in evaluating various traits which are not reported in the large-scale state, commercial, or county tests, e.g., harvestability (ease of shelling, ear retention, etc.) disease resistance, and staygreen.
The Ohio State University Agronomy Department conducts corn performance tests across Ohio. Test results are summarized each year in a bulletin (Ohio Corn Performance Test, Agronomy Department Series 215) and on a computer disk (ECAP 2.0 computer series). Hybrid testing results are also available from neighboring states.
Higher test weight is often considered an advantage from a marketing standpoint and therefore a desirable hybrid characteristic. However, there is little relationship between grain test weight and kernel breakage or nutritional value. The test weights of hybrids differing widely in kernel moisture percentage (e.g. short vs. full season hybrids) should not be compared because the drier hybrid has an unfair advantage. Test weight increases as kernel moisture decreases unless corn is immature, severely combine damaged, or dried at extremely high temperatures. Test weight is most effectively used as a criterion in hybrid selection when comparing hybrids of similar maturity. Hybrids with similar maturity ratings (i.e. days to black layer) may differ by as much as 2 to 4% kernel moisture during the harvest period because certain hybrids possess characteristics such as loose husks, thin seed coats, and small cobs which contribute to faster drydown rates.
Always select a hybrid based on its performance, not because it is a particular type of cross. Single crosses have the maximum hybrid vigor, and thus the greatest yield potential, followed by modified single crosses, three-way crosses, and double crosses. Hybrid blends (mixtures of two or more hybrids) are often used where risks or maturity need to be spread out. Blends are sometimes comprised of leftover seed from older, less productive hybrids. Blends rarely perform better than the individual hybrids comprising the mixture.
Many seed companies are marketing hybrids based on differences in hybrid response to management practices such as soil type, plant population, tillage, soil fertility, herbicides, and crop rotation. While some differences do occur among hybrids under various cultural practices, superior hybrids are often top performers regardless of cropping systems or practices. Usually it is a difference in hybrid maturity or an interaction with environmental conditions that accounts for the varying responses of hybrids to cultural practices.
Seed companies are using various genetic techniques to insert resistance or tolerance to specific herbicides into existing corn hybrids. In 1993, at least three companies (Pioneer, ICI, and Ciba-Geigy) will be marketing hybrids resistant or tolerant to imazethapyr (Pursuit) and imazaquin (Scepter) herbicides. The yield potential of these resistant types does not appear to differ from the original susceptible types, but herbicide resistant types may not have the yield potential of more recently developed susceptible hybrids. Growers must weigh the severity of their weed management problem against this possible lower yield potential before selecting herbicide resistant types.
If you are locked into a continuous corn cropping system, then consider rotating corn hybrids each year in any given field to partially offset the yield disadvantage of continuous corn. According to research in Minnesota and Iowa, hybrids often yield less when following themselves in continuous corn than when grown in rotation with other hybrids. Such hybrids should also be selected for high levels of resistance to diseases which are more likely to be a problem in continuous corn (especially continuous no-till corn).
Prepared by:
Peter R. Thomison
Extension Agronomist
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