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Hot weather during corn pollination

by Jeff Coulter, Extension Corn Specialist

Tassels recently became visible in many corn fields across Minnesota. This week a large percentage of the corn in Minnesota will be pollinating. Although air temperatures and soil moisture levels have been near optimal for corn in many areas of this region, hot weather is forecast for the second half of this week.

The critical period for avoiding stress in corn is the two weeks before and two weeks after tassel emergence, with the most important time being the week after tassels emerge. Heat stress generally has less of an impact on corn during pollination than drought stress, and typically does not occur until air temperatures exceed 86 degrees with dry soils or 92 degrees with adequate soil moisture and high humidity.

Drought and/or heat stress before pollination affects the number of potential kernels per row. It also can cause silk emergence and elongation to slow while accelerating or not affecting pollen shed, resulting in asynchrony between pollen shed and silk emergence. This can result in poor kernel set.

Combined drought and heat stress shortly after tassels emerge can cause exposed silks to dry quickly and be less receptive to pollen. The success of kernel set can be evaluated throughout and soon after pollination by carefully unwrapping husks and gently shaking ears, as silks detach from the ear within a couple days after successful pollination.

Drought stress following successful pollination is more common in Minnesota compared to during pollination. This results in the loss of kernels at the tips of ears, but kernel loss can occur in other patterns on ears if drought stress is intense or combined with other stresses.

For more educational resources on corn production, visit Extension’s corn production website at
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