Fall Scouting and Evaluating Field Test Plots and Demonstration Strips

Originally written September 18, 2004 | Last updated February 23, 2014

Progressive crop managers try new things every year and constantly evaluate their management practices. Some new practices work and fit into their management style, others don't. Lessons learned producing this year's crop will help with next year's crop.

Growers should continue scouting right through harvest. Growers need to monitor fields carefully, and plan harvest schedules to begin with fields where stalk and root deterioration appears worst. Below are some things to check in your fields yet this year for timing harvest, and to consider in your plans for next season. Record information. Keep a notebook or computer file. It is difficult to commit things to memory, especially two or three seasons into the future.

Fall Field Scouting

Check for ear-tip fill. Incomplete ear-tip fill is not necessarily bad. If kernels are filled out completely to the ear tip, plant populations are likely too low for conditions. Expect about an inch of underdeveloped kernels at the ear tip if plant populations are at a high enough level to optimize grain yield per acre.

Check kernel development on the ear. Look for differences in how well different hybrids have held up to management practices (i.e. herbicide application, irrigation stress, N stress, etc.) and weather stresses. Early stress from weed competition or low N will reduce kernel row number and kernel number per row. Severe heat and moisture stress during the first seven to ten days after pollination will cause kernels at the tip of the ear to abort. Stress around pollination reduces cell division and potential starch fill causing shallow kernel depth and lighter test weight.

Check the maturity of hybrids in your fields and relate back to planting and emergence dates. Following the rate of drydown using kernel milkline is a good way to predict the order fields should be harvested. In a typical year a common benchmark is that fields should be dented by the first week in September. It takes about 30 days to go from dent to black layer (physiological maturity); about 15 days to get to 50% kernel milk and another 15 days to black layer. Kernel moisture at black layer will average 32 to 35 percent. The tightness of the husk, thickness of the seed coat and daily weather conditions influence the speed of kernel drydown. After black layer formation several hard frosts followed by sunny weather with temperatures in the 80's and a slight breeze is the ideal drying environment.

Hybrids differ in the time it takes to reach harvest moisture from black layer. A rough estimate is that 15 to 20 GDUs/point of moisture are needed to lower the moisture from 35 to 25 percent. It takes 20 to 25 GDUs/point of moisture to dry the grain from 25 to 20 percent.

Scout for corn standability. Fields that have lodging problems can be identified and targeted for the earliest possible harvest. Look for visible symptoms and test stalk firmness by pinching the lower internodes with your thumb and forefinger. Healthy stalks are firm and can't be compressed. If a stalk can be compressed or feels soft, it is rotted and is a good candidate for lodging.

Check for rapid "die-down." The lower portion of corn plants in some fields deteriorates rapidly. Lower leaves first appear nitrogen-stressed, then turn brown and die. Other factors such as compaction, dry weather, herbicide injury or root pruning by insects can also cause these symptoms. Some of these plants may be experiencing low nitrogen availability due to losses from leaching and/or denitrification following excessive rain.

In most cases it is more likely due to remobilization of nutrients from the stalk to the grain, a sort of "cannibalism." Cool, cloudy days and warm nights produce low levels of photosynthesis (sugar production) during the day with high rates of respiration (sugar breakdown) at night. When the plant's nutrient availablity is limited due to low photosynthesis, sugars already produced and stored in the stalk are often "moved-out" (translocated) to help fill the ear. Another factor that might be responsible for rapid die-down is the development of pathogens that cause root and stalk rot. Wet soils and cloudy humid conditions favor these diseases. Corn stalks weakened by remobilization of nutrients to the ear are especially vulnerable to root and and stalk rotting organisms.

During combining inventory weed problems. Use a map and list details such as location of broadleaf and grass species, population density of the crop and weed, and response to herbicides. Watch for new weeds. Watch for any weeds that may be developing resistance to herbicides.

In preparation for next year, assess soil fertility levels by pulling soil samples.

Resist estimating yield differences between corn hybrids - measure it. Field variability alone can easily cause apparent differences of 10 to 50 bushels per acre. Make notes bout "ease of combining." Test weight and grain moisture can influence hybrid yield. There are "quickie" measures of potential grain yield, but you shouldn't expect much precision with these measures.

In general, there are two major categories of on-farm research trials. The first is replicated trials that try to account for field variability with repeated randomized comparisons. Examples include trials conducted by universities and by public and private plant breeders. The other type is non-replicated demonstrations such as yield contests, on-farm yield claims, demonstration/strip trials and farmer observation and experience.

Evaluating Research Test Plots

Field variability alone can easily account for differences of 10 to 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 to 10 hybrids. The best test plots are replicated (with all hybrids replicated at least three times).

Don't put much stock in results from ONE LOCATION AND ONE YEAR, even if the trial is well run and reliable. This is especially important in years with tremendous variability in growing conditions. Years differ and the results from other locations may more closely match your conditions next year. Use data and observations from university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.

A few suggestions on how to evaluate research test plots:

  1. Walk into plots and check plant populations. Hybrids with large ears or two ears per plant may have thin stands.
  2. Scout for pest problems. Hybrid differences for pest resistance and tolerance should be monitored and noted all season, but will be most apparent in the fall. Counting dropped ears is a good way to measure hybrid ear retention and tolerance to European corn borers.
  3. Check for goose-necked stalks. This is often root pruning caused by corn rootworms. Hybrids differ in their ability to regrow pruned roots.
  4. 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.
  5. Differences in standability will not show up until later in the season and/or until after a wind storm. Pinch or split the lower stalk to see whether the stalk pith is beginning to rot.
  6. Break ears in two to check relative kernel development of different hybrids. 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.
  7. Visual observation of ear-tip fill, ear length, number of kernel rows, and kernel depth, etc. don't tell you much about actual yield potential. Hybrid differences are common for tip kernel abortion ("tip dieback" or "tip-back") and "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. Be careful with test plots consisting predominately of one company's hybrids. Odds are stacked in their favor!

Evaluating Demontstation or Strip-Trial Plots

Every fall many farmers visit and evaluate hybrid demonstration plots planted by seed companies and county Extension personnel, among others. When checking out these plots, it's important to keep in mind their relative value and limitations. Demonstration plots may be useful in providing information on certain hybrid traits, especially those that are usually not reported in state corn performance summaries.

Use field days to make careful observations and ask questions, but reserve any decisions until you have seen the "numbers." Appearances can be deceiving.

PLANT/EAR 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 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 worsened by 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.

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. Keep in mind that uneven emergence and development may make such comparisons difficult because late emerging plants are "spindlier".

DISEASES. 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.

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.

LODGING. 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 variety plot is affected by stalk rot in late August and early September, evaluate stalk lodging of the different hybrids. Most agronomists characterize plants with stalks broken below the ear as stalk lodged plants. In contrast, corn stalks leaning 45 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 (as it did this year) and as late as harvest maturity. Both stalk and root lodging can be affected by hybrid susceptibility, environmental stress (drought), insect and disease injury.

Root lodging may be associated with western corn rootworm injury. However, much root lodging 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 cornfield 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).

TRANSGENIC TRAITS: Because damage from European corn borer (ECB) and western corn rootworm (RW) can be very localized, strip plot demonstrations may be one of the best ways to assess the advantages of ECB Bt and RW 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 first year 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 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. 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. 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.

Remeber that yield is not a beauty contest. Some "ugly" hybrids are good performers. Don't over emphasize results from one type of trial. Use data and observations from university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.

Buy hybrids ... don't be sold based on fancy result books and plot signs, flags, streamers, caps, brats, etc.

Remember safety as you move into the harvest season this year.


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