By Peter Thomison, Corn Cropping Systems Extension Specialist
This is the time of year when many farmers visit and evaluate hybrid demonstration plots planted by seed companies and county Extension personnel, among others. When we experience a year like 2016 in which drought and heat impacted corn performance in many fields, it’s likely we will see some striking differences among hybrids in demonstration plots.
When evaluating these plots, it’s important to keep in mind their relative value and limitations. Demonstration plots can be useful in providing information on certain hybrid traits that are usually not reported in state corn performance summaries. The following are some traits to consider when examining hybrid demonstration plots.
Corn reaches it maximum plant height soon after tasseling occurs. Remember that although a taller hybrid may have a lot of "eye appeal," it may also be more 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. 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 in the fall may be greater with high ear placement. Plots that have been subjected to early season (V7 or earlier) defoliation caused by hail or frost often have lower than normal ear height.
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. Also keep in mind that uneven emergence and development may make such comparisons difficult because late emerging plants are “spindlier”.
During the grain fill period, leaf diseases can cause serious yield reductions and predispose corn to stalk rot and lodging problems at maturity. Ear rots can also impact yield and grain quality. 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 considerably in their ability to resist infection by these diseases. Demonstration plots provide an excellent opportunity to compare differences among hybrids to disease problems that have only occurred on a localized basis. Look for differences in resistance to northern corn leaf blight, gray leaf spot and diplodia ear rot. Check to see if foliar fungicides have been applied and what crop rotation has been followed. Typically you’ll encounter more severe foliar disease problems in no-till, continuous corn.
Hybrids will likely differ widely when faced with strong stalk rot pressure. Begin checking plants about 6 weeks after pollination (at about black layer) 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.
Perhaps as important as stalk rot resistance is the stalk strength characteristics of a hybrid. Sometimes, superior stalk strength will limit the adverse effects of stalk rot. If your demonstration plot is affected by stalk rot in late August and early September, evaluate stalk lodging of the different hybrids. The best time to make this assessment is shortly before plot harvest. Most agronomists characterize plants with stalks broken below the ear as “stalk lodged” plants. In contrast, corn stalks leaning 30 degrees or more from the center are generally described as “root lodged” plants; broken stalks are usually not involved.
Root lodging can occur as early as the mid- to late vegetative stages and as late as harvest maturity. Both stalk and root lodging can be affected by hybrid susceptibility, environmental stress (drought), and insect and disease injury. Root lodging may be associated with western corn rootworm injury. However, much root lodging in Ohio occurs as the result of other factors, i.e., when a hybrid susceptible to root lodging is hit by a severe windstorm.
A hybrid may be particularly sensitive to root lodging yet very resistant to stalk lodging. A corn field may exhibit extensive root lodging in July but show little or no evidence of root lodging at harvest maturity in September (except for a slight “goose necking” at the base of the plant). In recent Ohio State University tests evaluating hybrid by plant population interactions, we observed less recovery in certain hybrids when plant populations exceeded 34,000-35,000 plants per acre.
Aka "brittle snap,” is pre-tassel stalk brakeage caused by wind. The problem has become more common in Ohio in recent years because of the greater frequency of severe wind storms in late June and mid-July. Vulnerability to green snap damage varies among hybrids. Breaks in the stalk usually occur at nodes (along nodal plates) below the ear.
Because damage from European corn borer (ECB), western corn rootworm (RW), and western bean cutworm (WBC) can be very localized, strip plot demonstrations may be one of the best ways to assess the advantages of ECB Bt, RW Bt and WBC Bt corns. The potential benefit of the ECB Bt trait is likely to be most evident in plots planted very early or very late; the potential benefit of the RW Bt trait is likely to be most evident in plots planted following corn or in a field where the western corn rootworm variant is present.
Husk Coverage/Ear Angle
Hybrids will vary for completeness of husk coverage on the ear as well as tightness of the husk leaves around the ear. Ears protruding from the husk leaves are susceptible to insect and bird feeding This year there have been reports of hybrids exhibiting short husks in states to the west of Ohio.
Husks that remain tight around the ear delay field drydown of the grain. Hybrids with upright ears are often associated with short shanks that may be more prone to ear and kernel rots than those ears that point down after maturity. This relationship received considerable attention in 2009 when Gibberella ear rot problems were widespread across the Eastern Corn Belt. However, we’ve observed that differences in ear “orientation” among hybrids can be strongly influenced by growing season and plant density. Also, under certain environmental conditions, some hybrids are more prone to drop ears, a major problem if harvesting is delayed.
The following are some additional points to consider during your plot evaluations.
1. Field variability alone can easily account for differences of 10-50 bushels per acre. Be extremely wary of strip plots that are not replicated, or only have "check" or "tester" hybrids inserted between every 5-10 hybrids. The best test plots are replicated (with all hybrids replicated at least three times).
2. Don't put much stock in yield results from ONE LOCATION AND ONE YEAR, even if the trial is well run and reliable. Don't overemphasize results from ONE TYPE OF TRIAL. Use data and observations from multiple university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.
3. Initial appearances can be deceiving, especially visual assessments. Use field days to make careful observations and ask questions, but reserve decisions concerning hybrid selection until you've seen performance results.
4. Walk into plots and check plant populations. Hybrids with large ears or two ears per plant may have thin stands.
5. Break ears in two to check relative kernel development of different hybrids. Use kernel milk line development to compare relative maturity of hybrids if hybrids have not yet reached black layer. Hybrids that look most healthy and green may be more immature than others. Don't confuse good late-season plant health ("stay green") with late maturity.
6. Differences in standability will not show up until later in the season and/or until after a windstorm. Pinch or split the lower stalk to see whether the stalk pith is beginning to rot.
7. Visual observations of kernel set, ear-tip fill, ear length, number of kernel rows and kernel depth, etc., may provide some approximate basis for comparisons among hybrids but may not indicate much about actual yield potential. This year we’ve seen differences in tip kernel abortion (“tip dieback” or “tip-back”) among hybrids and heard reports of “zipper ears” (missing kernel rows). Even if corn ear tips are not filled completely, due to poor pollination or kernel abortion, yield potential may not be affected significantly, if at all, because the numbers of kernels per row may still be above normal.
8. Find out if the seed treatments (seed-applied fungicides and insecticides) applied varied among hybrids planted, e.g. were the hybrids treated with the same seed applied insecticide at the same rate? Differences in treatments may affect final stand and injury caused by insects and diseases.
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