One of the most important management decisions corn growers make each year is selecting corn hybrids. Results of state corn performance trials provide detailed comparisons of hybrids for different characteristics across a wide range of environmental conditions. However, local corn hybrid demonstration plots can be useful in providing information on certain hybrid traits, especially those that are not usually reported in state corn performance summaries. There are a number of these plots established each year by various seed companies, county Extension personnel, and local FFA clubs. Many growers also conduct on-farm tests to evaluate hybrids under their own conditions.
The following are some of the genetic characteristics to observe during the growing season that can influence a hybrid's overall performance and yield potential.
FLOWERING DATE. During the tasseling and pollination period, determine the difference between hybrids in date of tassel and silk emergence. Planting a range of hybrids with different silking maturity dates may help spread the risk of heat or moisture stress occurring during flowering. Sometimes, there isn't that much difference in silking dates between "early" and "late" hybrids.
SILK EMERGENCE. Silks should emerge from the ear shoots within a day or two after the beginning of pollen shed. Silk emergence in corn is often delayed when plants are subjected to considerable moisture stress. Ironically, pollen shed is often speeded up under moisture stress, so the opportunity for pollen grains and ovules to come together ("nick") is decreased. If you have the opportunity to observe a variety plot that is under moisture stress, make sure you pay attention to how well silk emergence occurs in the various hybrids. Hybrids can differ significantly in their ability to tolerate moisture stress and continue to elongate silks.
PLANT HEIGHT. Corn reaches it maximum plant height soon after tasseling occurs. Remember that although a big tall hybrid may have a lot of "eye appeal," it may also be prone to stalk lodging in the fall. Unless your interest is primarily silage production, increasing plant height should not be a major concern. Generally later maturity hybrids are taller than earlier maturity hybrids.
EAR HEIGHT. Big ears placed head high on a plant translate to a high center of gravity, predisposing a plant to potential lodging. The negative effects of stalk rot on stalk lodging n the fall may be worsened by high ear placement.
LEAF ANGLE. Hybrids vary in the angle that the leaves point toward the heavens. So-called "upright leaf" hybrids are often thought to possess greater yielding ability due to their ability to capture more sunlight throughout their leaf canopy.
BRACE ROOTS. Brace roots are part of a corn plant's permanent root system that develop at stalk nodes above the soil surface. If the surface soil is moist and not excessively hot, brace roots will penetrate the soil and proliferate. Brace roots provide a certain amount of structural support to the plant during strong winds. If the upper soil layers remain moist during grain fill, brace roots will also scavenge soil nutrients for use by the developing ear.
STALK SIZE. Generally speaking, a thicker stalk is preferable to a thinner one in terms of overall stalk strength and resistance to stalk lodging. As you inspect a test plot, you will see distinct differences among hybrids for stalk diameter. However, also check that the hybrids are planted at similar populations. As population increases stalk diameter generally decreases.
LEAF DISEASES. During the grain fill period, leaf diseases can cause serious yield reductions and predispose corn to stalk rot and lodging problems at maturity. The onset of leaf death shortly after pollination can be devastating to potential yield, since maximum photosynthetic leaf surface is needed to optimize grain yield. Hybrids can vary tremendously for their ability to resist infection by these diseases. Pay close attention during the 6 to 8 weeks after pollination for development of leaf diseases among hybrids in a test plot.
STALK ROTS. Hybrids will likely differ widely when faced with strong stalk rot pressure. Begin checking plants in late August or about 6 weeks after pollination by pinching lower stalk internodes with your thumb and forefinger. Stalks that collapse easily are a sure indicator of stalk rot. Remember that hybrids with thicker stalks may be in plots having thin stands.
STALK LODGING. Perhaps as important as stalk rot resistance is the stalk strength characteristics of a hybrid. Sometimes, superior stalk strength will overcome the effects of stalk rot. If your variety plot is overcome with stalk rot in late August and early September, be certain to evaluate the stalk lodging resistance of the different hybrids.
HUSK COVERAGE. Hybrids will vary for completeness of husk coverage on the ear as well as tightness of the husk leaves around the ear. Ears that protrude from the husk leaves are susceptible to insect and bird feeding. Husks that remain tight around the ear delay field drydown of the grain. As a test plot nears harvest maturity, compare hybrids for these characteristics.
The following are some additional points to consider during your plot evaluations.
The best test plots are replicated (all hybrids repeated at least twice) or have a "check" hybrid repeated every other hybrid.
Prepared by:
Peter R. Thomison
Extension Agronomist
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