As the corn plants approach completion of grain fill about 40-50 days after pollination, some individual pants will change in color. These changes can indicate the effect of the season on the plants.
Plants in which all leaves are gray, then brown, pointing towards the ground, have wilted because the roots could not provide sufficient water to meet transpiration needs. These have root rot caused by lack of sufficient sugars moved from the leaves, allowing soil microbes to invade and destroy the root tissue. Movement of limited supply of sugar moved to the grain was preferred over movement to roots. That individual plant did not produce sufficient photosynthesis to maintain both the root life and grain fill. Such plants will develop hollow stalks and be invaded with fungi. These plants are likely to lodge by harvest time.
Some individual plants may turn red gradually during this time period. These plants usually have only a few kernels. Sugars accumulate in the leaves because not enough hormone driven transport is causing the sugars to be moved, or perhaps because of interference of movement because of insect damage to the vascular system. Chemical processes in the cells with accumulating sugars transpose the sugar molecules to anthocyanin, providing the red color in the leaves. This is usually an indication of poor pollination, perhaps because this individual plant emerged late as a seedling and therefore missed much of the pollen from other plants.
Nitrogen deficiency is indicated when several plants have yellow lower leaves while upper leaves remain green. This is common in areas of fields that were water-logged.
Desired color of maturing plants indicating a successful yield has white ear husks while other leaves remain green and turgid all the way to completion of grain fill, about 55 days after pollination. The occasional wilted plant can be a sign that the field got maximum grain allowed by that season’s environment.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.