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Are We Looking at the Crops Right?

July 13, 2001
As most cornfields move into (and through) the pollination process, the questions continue about the "real" state of the crop. We notice that the percentage of the crop ranked as "good" or "excellent" is lower than it was last year at this time, and modest price rallies in the past 2 weeks suggest that many people have the expectation that this year's crop isn't quite "up to snuff." What's the real story?

The crop in 2001 went in about as early as the 2000 crop, and temperatures this year have generally been higher than they were a year ago. Rainfall in June was very plentiful last year, but in many areas this year, there were at least short periods during June when the crop showed some symptoms of lack of water. By the end of June, the crop in 2000 looked fantastic, while this year the crop looked better than average but not as uniformly good as last year's. Still, most fields entered or are entering the pollination period without too many noticeable problems, at least in most of the state. As we noted 2 weeks ago, June weather was more conducive to root growth than the wet weather of last year. But in areas where there was dryness, the crop is not quite as tall as last year, and the color in most fields is not the deep green it was a year ago. The biggest difference is temperature: Last year, it was August before we hit 90°F, while this year it has been above 90 a number of times since early May. It is probably the lower night temperatures that provide the real advantage from low temperatures. Lower night temperatures tend to limit respiration and to thereby keep more of the plant sugars available for growth and development. If we had a good way to measure the "sugar status" of the crop, last year's corn crop would have this year's beat.

Is the lower rating of crop condition likely to mean much at the end of the season? For the reasons mentioned above, we probably can't expect kernel number and size to be as high this year as they were last year. On the other hand, the lack of rainfall after early July, leaf diseases, and what was likely a marginal root system combined to reduce yields and stalk quality last year. In general, crop ratings last year stayed high in August, longer than the actual crop condition probably justified, though the remarkable conditions through pollination still produced high yields statewide, and in southern Illinois where rainfall was better, the yields were outstanding. This year, we haven't had many leaf diseases, and the root system may be better; but we also have a crop that has encountered more stress up to now, and in areas missed by recent storms, that stress is worsening. How this will play out is almost entirely dependent on rainfall during the next 6 weeks. Cooler-than-normal August temperatures would also be very useful, but if the dry weather continues or if August is normal or above normal in temperature, it is likely that we will not have either average or top-end yields as high as we saw in 2000 and in 1994.

The story in soybeans is different from that in corn. In general, the lack of excessive rainfall in most areas during the past month has resulted in less drowning in the low spots than we've had some years. Stands tend to be fairly good, and crop color is probably about average. But as I noted recently, soybeans at this stage are about as easy to "call" as knee-high or waist-high corn; we can see if there are serious problems in stands or crop health, but the conditions that will produce yield are still in the future. Weather conditions that will be conducive to high corn yields will be favorable for soybeans as well, but to turn a good crop into an excellent one, the conditions for soybeans usually need to last about 2 weeks longer than for corn. For both crops, how many of the next 50 to 60 days the crop will be able to maintain maximum photosynthetic rates will largely determine the yield we harvest this fall.--Emerson Nafziger

Author: Emerson Nafziger

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

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