If a corn plant draws more carbohydrates to the ear during those critical 60 days after pollination than it can supply with current photosynthesis and storage in the stalk, it depletes the supply needed to keep root cell’s metabolism. The deterioration of root cell metabolism allows invasion of organisms in the soil and inability of the roots to transport water to the plant parts above the soil. Transpiration from the leaves continues until all available water is gone. Then the plant wilts. Symptoms of the wilt become slightly visible for a few days before all leaves turn gray and droop. We call this premature death. These wilted plants occur as individuals, often surrounded by green plants that did not overdraw on its carbohydrate supply to fill its kernels. Often these individual wilted plants have more kernels than those adjacent green plants or have excess photosynthetic stresses.
The wilted plants initially have green outer rind to the lower stalk, but the pith tissue inside the stalk has puled away from the outer rind, as part of the wilting process. This weakens the stalk strength by one third. The outer rind slowly turns from a green color to yellow and shows symptoms of invasion of fungi as they digest the remaining cellulose and proteins in the stalk cells, further weakening the stalk strength.
The critical stresses leading to stalk rot occur during the kernel fill period, those 60 days after pollination. If a plant makes it through that time without wilting, it probably will not get premature root ands stalk rot by normal harvest time. Inspection of corn plants about 60 days after pollination allows the grower to access the to predict probability of stalk rot and lodging in the field that season. Individual gray plants with yellow and brown color to outer rind of the lowest 2-3 above-ground nodes are most likely to lodge with slight wind pressure. These plants easily fall with slight pressure. One can also easily pull the plants up from the soil as the dead roots offer little resistance.
Why did that plant commit more to kernel fill that its photosynthesis could supply? Was it shaded by adjacent plants because of inadequate spacing of seed, did it have excess damage to leaves from pathogens or insects. Did the environment of the roots cause less root mass or destruction from pathogens or insects? Perhaps the genetics of the hybrid encouraged a higher kernel number in that environment than could be supported under the photosynthetic stress of the season.
Having a few early wilted plants in a field can be a sign that the hybrid maximized its ability to produce grain yield for that season’s environment. One can learn a lot with inspection of the field shortly after the 60-day kernel fill period.
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.