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Notes on the Wheat Crop

April 17, 2003

Travels in southern and northern Illinois over the past 2 weeks have shown the 2003 wheat crop to be in mostly good condition, after a rather slow start last fall. Though winter conditions were relatively cold and snow cover was limited, the crop survived to spring green-up quite well, though with fewer tillers and less vegetative growth than we would like to see. In many fields, rows were easily visible, and ground cover was probably less than 50% throughout dormancy. But over the past month, we have had more than average amounts of the relatively dry, cool, and sunny conditions that we need for such a crop to produce more tillers and thus boost its yield potential. Nitrogen has been applied to almost the entire crop, and crop color is good. Crop growth has been rapid in the past 2 weeks, though the crop is only about average in its developmental stages. Even the frosty conditions a few mornings have probably helped reduce pressure from insects that might spread disease. Wheat does not suffer from temperatures in the upper 20s, at least until it's in boot stage or beyond.

One problem that has been noted in several fields, mostly in northern Illinois, is that of injury from nitrogen application. While we can usually put solution N (UAN or dilute ammonium sulfate) on the crop during dormancy without much problem, the limited growth of the crop last fall and some unpredictable temperature fluctuations before and after application have in some fields resulted in loss of leaf area and even some death of plants, especially in overlap areas. Such injury seems to require that the wheat plants be a certain size, such that leaves do not intercept all of the solution but rather allow it to run down into the whorl, where it can injure the growing point and kill the plant. Smaller plants, with less leaf area and leaves more upright, may intercept little of the solution and hence escape injury. The surest way to prevent such damage is to use dry forms of nitrogen. If solution N is used, it might be best to wait to put it on until plant growth is adequate to more or less cover the soil surface, even if that means waiting to apply N until there has been some spring growth. Applying all of the N at planting works for some people, but warmer fall weather can cause excessive growth and there is more time for such N to be lost under wet conditions.

As the crop enters the jointing stage and moves toward heading, yield potential will start to become clearer. Maximum tiller number is set by the time plants joint (when we can feel the first node at the base of the plant, usually about the time plant height reaches 10 inches or so), but the number of tillers that form heads can change. Cool, dry conditions will favor head numbers, which are usually associated with yield. Still, guessing at wheat yield before heading is about as accurate as guessing yields of a corn crop that's 3 feet tall in the middle of June; most of the problems that cause yield loss are yet to come.--Emerson Nafziger

Author: Emerson Nafziger

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