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Be on the Alert for Stalk-Quality Problems

September 8, 2000
Although windstorms were not particularly widespread in Illinois this growing season, there are some reported problems with corn that is flat or with stalks that are weak and subject to lodging. In the most severe cases, which tend to coincide with dry conditions in July and August, stalks in some fields are starting to break even without strong winds

Even though much of the growing season has been favorable over most of Illinois, good pollination and a good start to grainfill were followed by relatively dry weather in parts of the state. The temperatures and humidity have also been high in late August. As a result, leaves have dried up prematurely in the dry areas, and kernels have filled by depleting stalk reserves of sugar faster than the leaves can replenish these reserves. Most kernels that are filled or nearly filled have good size, so the depletion of stalk reserves may be more widespread than usual.

Although the depletion of stalk reserves to fill kernels results in more yield, it also reduces the ability of the stalk to maintain its strength and to resist infection by microorganisms. As a result, stalk rots move in from the soil, and stalks can weaken very quickly.

In areas that have been dry, it is critical that producers examine fields to see whether stalk quality has deteriorated. Pinch stalks below the ear to see if they are soft, or grasp stalks above the ear and push them over 4 to 6 inches to see if they break. Especially where stalks break over with little resistance, the danger of stalks breaking quickly in large numbers is high.

The only practical remedy for weak stalks is to harvest early. Corn is physiologically mature when the kernels have a black layer at their base when the tip of the kernel is scraped. If it has been dry for so long that the leaves dried up in mid-August, then grainfill probably ended early, and kernels will likely be smaller and less dense than normal. No matter how grainfill ends, the black layer will form when sugars are no longer available to move into the kernels.

By black layer, grain moisture is typically between 30% and 32%, though it might be higher if grainfilling ended prematurely. With higher fuel costs, many people are reluctant to harvest when grain moisture is above 25%, especially in years such as this with early maturity and warm weather; grain moisture should drop very fast in early-planted fields that are already mature or will mature within the next week. If the crop has good stalk quality, early harvest and extensive drying should not be necessary, but if the stalks are weak, losses from lodging can easily exceed drying costs.

Corn that has broken over sometime in August, ears that are beneath the stalk, and leaves on plants that are more or less horizontal will dry slowly. On plants where green-leaf area ended up on the ground and lost its orientation to the sun, or where roots pulled from the soil and could no longer take up water, yield will also be reduced. Ears in contact with the soil may pick up ear rots more easily. One report from a person who flew over fields indicated that a considerable amount of corn in the area running south of I-80, from the central to the eastern part of the state, may be more lodged than it looks from the road. If you had a windstorm anytime in August, you might want to see if fields are more damaged than they appear to be from the outside.

Where windstorms have already caused lodging, harvest will be difficult. Reels that attach to cornheads and help feed stalks into the gathering units can be helpful, though very weak stalks break so easily that they might not always work well. Such reels may be available from parts of western Illinois where they were needed last year but probably won't be needed this year. Driving the combine in the same direction may also be necessary in some fields.

Corn that did not fill properly often retains sugars in the kernels that were not converted to starch. Such sugars make the grain dry more slowly, and they may caramelize at high drying temperatures, resulting in dark discoloration. Where grainfill has been incomplete, it may be best to feed this grain to livestock, particularly if there is a possibility of storing the grain in sealed silos without having to dry it.

In a year when growing conditions have been favorable statewide, it can be difficult to anticipate problems or to deal with them when prices are so low. But stalks might be weak even in fields where the crop looks good, and care must be taken not to lose some of the high yields that exist in most fields.--Emerson Nafziger

Author: Emerson Nafziger

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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