No. 17 Article 4/July 16, 2004

A Few Bumps in a Smooth Road

While the overall condition of corn and soybean crops in Illinois continues to be good, no season is without its problems, including this one. On the positive side, warm temperatures continue to push development, and many parts of the state have already received as much rain as normally falls during the entire month of July. We have almost never had low corn yields when July rainfall is above normal, and the fact that the crop is so far ahead of normal is even more positive. It appears that pollination was successful in most areas, though reductions in kernel number due to silk clipping by insects can be a hard-to-see problem. If you have any reason for concern, remove husks about 2 weeks after silking, and see whether silks easily pull off kernels. If they remain attached, they were not fertilized.

There are areas damaged by excessive water that are not visible unless you take to the air to see them. But the spell of dry weather before early July allowed some recovery, and leaf color, which is a prime indicator of overall plant health and activity, is very good in most fields. One of the best ways to assess general potential of a corn crop now is to see how much sunlight is getting through the canopy and hitting the ground. The best crop has very little sunlight getting through the canopy; it should be almost dark on the soil surface at noon on a sunny day.

Storms have done some damage this week in some Illinois cornfields. Coupled with some root systems injured by corn rootworm, it's likely that parts of some fields are lying flat, some for the second time. Plants that lodge before tasseling often can "gooseneck" at least partly back upright and can be quite productive, though they suffer from some root dislodging and so can be more subject to dry weather. If the crop has pollinated when lodging occurs, plants have much less ability to grow back upright, due to increased "woodiness" of the lower stem. This woodiness is important for stalk strength and standability, and so is generally positive; it does, though, mean that the stalk becomes "set" and less flexible.

Once plants are flat on the ground at or after the "roasting ear" stage (R3), they often fail to function very well, and their yields are often low. Usually only part of the root system is still engaged in the soil, and much of the leaf area is shaded. If some stalks stay standing while their neighbors lodge, they will compensate some. But the general prognosis for corn plants lodged during grain fill is not positive.

Soybean plants in most fields continue to grow rapidly, and flowers are present at most nodes in most fields. Some of the flowers that appeared in early June have developed into pods, giving stems the rather unusual feature of larger pods near the base and flowers only at younger nodes. This confuses the staging a bit, but the new flowers represent the real yield potential of most of these plants, and we probably should consider them in R2 (full flower), even if lower pods suggest that they're in R3 or even later.

Pods near the base of the stem often do not fill very well if rapid growth results in large leaves in the upper canopy that then shade the lower leaves. Most of the sugars to feed each pod come from the leaf attached nearest that pod on the stem, so shaded leaves mean unfilled pods. In 2003, canopies ended up very dense in many cases, and lower pods often aborted or failed to fill seeds as a result. Leaf growth has been more modest in 2004, at least up to now, and the more favorable temperatures this year will likely mean more timely pod development and a better "balance" between pod and canopy development.

Illinois wheat yield is pegged in the July report at 58 bushels per acre. Not a record, but still quite good given the warm, wet weather of May and the early harvest. Variety test reports will soon be posted here. --Emerson Nafziger

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