The effect of high heat and drought on corn
High temperatures can cause problems in corn even when soil moisture is adequate — and will compound problems in drought-stressed corn. Hot, dry conditions are particularly damaging during pollination (VT-tassel through R1-silk). Much of the corn crop in Kansas is just now entering this critical period for determining grain yield.
Effects of stress at pollination time
There are several reasons why the four weeks centered around pollination are so critical for determining grain yield. During the last couple of weeks before tassels emerge, the potential ear length is being determined. Extreme stress at this time can reduce the number of kernels per row – affecting potential ear size. Extremely high temperatures prior to and during pollen shed can reduce pollen viability.
Drought stress can slow silk elongation so much that the pollen may be shed before the silks emerge. Lack of water can also result in poor tassel exertion. Combined with the leaf rolling associated with drought stress, the pollen may be shed before the tassel has emerged. Even if pollination does occur successfully, kernels may abort during the first several days of development under severe heat/drought stress. All of these factors can reduce successful pollination, kernel set, and kernel development, reducing the number of kernels per acre – the greatest determinant of grain yield.
Management options for stressed corn
Where dryland corn has been under severe drought stress, you’ll have to decide whether to let it go and hope for some kind of grain yield, salvage the crop for silage or hay, or leave the crop in the field for its residue value. It likely will pay to wait until after pollination is complete before making this decision to get some idea of kernel set. If kernel set is good, the ears at least have the potential to produce grain. If kernel set is severely reduced, the first step is to estimate potential grain yield based on kernel numbers per acre and average to slightly below average kernel size. This can help you make the grain vs. forage decision.
Economically, should you leave the corn or cut it for silage or hay, or leave it for residue? The value of the residue for moisture retention, soil quality, and future crop productivity will vary depending on the situation, and can be hard to quantify -- but it is considerable. As for the silage/hay vs. grain decision, if the yield potential is less than 25 bushels per acre, it’s probably best to cut it for silage or hay. If the yield potential is 50 bushels or more, it’s probably best to harvest it for grain. If the yield potential is between 25 and 50, the decision will depend on the price of corn, the quality of the silage, and on a producer’s ability to use or sell the silage.