Patches or areas of yellow-looking plants and less than ideal root systems are common in many corn fields in northern Illinois. Can anything be done to improve these plants? Emerson Nafziger, University of Illinois Extension crop specialist, addressed this question in the recent Pest Management & Crop Development Bulletin.

Is there anything that can be done to improve root systems in a corn crop? Many fields were planted into soil conditions that were less than ideal. At best, cultivation might help break up a hard crust and thus introduce some oxygen into the soil. Roots that most need aeration are near the plant and cultivation close enough to disturb the soil in this zone often breaks roots, doing more harm than good. Cultivation can also mulch the surface of the soil and actually slow the movement of water to the soil surface. This actually reduces the rate of evaporation. Leaves that are yellow are not photosynthesizing very well, so they are not using water very fast. Such plants will be slow to recover root function due to slow drying of the soil.

Why is corn so yellow, even where nitrogen was applied before or after planting? This problem is directly related to the crop standing in saturated, low-oxygen soils. Root systems have suffered damage and are physiologically unable to take up nutrients very well. Roots that are in water suffer from low oxygen and also from a buildup of carbon dioxide, which is toxic. They also are not fed very well by sugars from the top of the plant, so energy needed to take up nutrients may be in short supply. Another reason for the poor color is that nitrogen may be depleted near the roots, thus causing a deficiency of nitrogen. Flooding and low oxygen make plants more vulnerable to root rotting organisms, and in some cases part or most of the root system may be lost to disease.

Aerating through drying might help roots to start to regrow, but if roots need to regenerate instead of just revive, recovery might be slow.

Is there anything to do to help plants green up? Until the soil dries out to allow roots to function better, there may be little we can do to help. The key is to have root systems recover and that is best accomplished by having the soils dry out.

Nafziger's article can be found at http://www.ipm.uiuc.edu/bulletin/article.php?id=966