Stress Effects on Corn

The components of corn yield include ears per acre, kernel rows per ear, kernels per row, and kernel weight. The number of ears per acre is usually set by the V6 stage of corn growth and by V12 the number of kernel rows, kernels per ear and ear size are determined. Corn product genetics have a big influence on these yield components but environmental stress, root feeding by rootworms, nutrient deficiencies, and leaf defoliation can also have a strong effect. The potential number of kernels per row is determined around V18. Drought stress can cause a lag between pollen shed and silking at this time and may cause up to a 4% reduction in yield potential for each stress day.

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Potential yield loss during grain fill can occur from stand loss, incomplete kernel set, decreased kernel weight, and premature plant death.2

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  • The plant compensates for stand loss prior to pollination by increasing the number of kernels on surviving plants or with greater kernel weight. Once ear size is set during grain fill, the plant can only respond by increasing kernel weight.
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  • Incomplete kernel set may be caused by insect feeding damage to silks, periods of high temperatures, low humidity and low soil moisture that desiccate silks, or pesticide injury. Kernels are most susceptible to abortion during the first 2 weeks following pollination, particularly kernels near the tip of the ear.2 Kernel abortion may be caused by severe drought or nutrient deficiencies (particularly nitrogen) during the blister or milk stages of growth. Extensive leaf loss around pollination caused by leaf diseases or hail can also cause kernel abortion. Consecutive days of overcast, cloudy conditions may reduce photosynthesis enough to cause abortion of ovules.
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  • Decreased kernel size and weight may be caused by severe stress (insect damage, leaf loss from hail or disease, pre-mature frost) during the dough and dent stages of grain fill.2 A killing fall frost, prior to physiological maturity, can cause premature leaf or whole plant death. Whole plant death can cause premature black layer development, resulting in incomplete grain fill and lightweight, chaffy grain. Severe stress that occurs during the grain fill period can cause premature kernel black layer formation due to the reduction of photosynthate to the developing kernels.3
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  • Stalk rots in corn can be caused by favorable early growing conditions followed by stress after pollination. Stress may be the result of leaf or stalk injury, compaction, low potassium with high nitrogen fertilizer rates, or injury form root feeding insects. Stalk rots can result in premature plant death, lodging or lightweight kernels.
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Silking Stage (R1) The first 7 to 10 days are critical because cell division occurs which determines kernel number and the potential size of kernels. Severe stress can cause an average of 7% loss in yield potential for every day of stress.1

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Blister Stage (R2) The developing kernels are whitish "blisters" on the cob. Severe stress can abort kernels during the pre-blister and blister stages of growth. Kernel abortion due to stress is less likely in the R3 milk stage than at the blister stage.

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Dent Stage (R5) Estimated yield loss due to total plant death at full dent is about 40%, while total plant death at half-milk line would decrease yield by about 12%.4

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