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Crops Respond to Warmer Weather

June 15, 2001
In 2000, it was August before most areas of Illinois first experienced temperatures of 90°F. That will not repeat in 2001; we have already had several days in the 90s, including 3 or 4 such days just this week. As we had earlier suggested would happen, the corn crop has responded well to these warm temperatures and the sunshine that has accompanied them. Leaf color has improved greatly, and with a few exceptions, much of the corn has entered the rapid-growth stage, with increases in height of several inches per day in many fields. Corn under such conditions goes from knee high to waist high to head high in a matter of 10 days or so.

The return of warmer weather has most people forgetting about the worries of just a week ago, when the weather was cool and wet and crop color was not very good. As the crop is now showing, we probably did not lose much yield potential to the May weather, even though it often seemed more like March than May. To many people's surprise, May growing degree-day (GDD) accumulations were actually above normal during May, primarily because we had some very warm days with GDD accumulations above 20 and the cool days did not have GDD accumulations low enough to cancel out the warm days.

We have had some reports of "rootless" corn, usually in no-till with certain herbicides applied. With rain to moisten and soften the surface soil, some of these plants will be able to establish their nodal root system and may recover well. There is little we can do to encourage this, though some people have tried to cultivate to provide soil around the base of the plant. In general, plants that have reached the 6-collar stage without a nodal root system probably will not catch up fully with their neighbors and so will have lower yield.

Soybean plants in most fields are still rather pale in color, as the nodules start to form. Within a week or so, or by the time plants have three or four trifoliolates expanded, color should return to normal. Stands of soybeans are lower than desired in fields where it has been excessively wet, but most fields probably have enough plants to justify keeping. Plant numbers of three or more per square foot probably do not need to be replanted if the plants are healthy, but many fields with this population in some areas will probably have areas with even fewer plants, and so some "repair planting" may be needed.

Wheat is ripening rapidly, and harvest is under way in the southern end of the state. Leaf health remained reasonably good in most fields up through maturity, so test weights and yields should be good, except in fields where armyworm defoliated plants earlier. Even in such fields, yields might be better than expected due to the favorable conditions after flowering.--Emerson Nafziger

Author: Emerson Nafziger

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

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