High Temperature Injury in Wisconsin Corn Fields

July 20, 1995 2(18):130

Joe Lauer, Corn Agronomist

The high temperatures last week may be responsible for the upper leaves on corn turning brown. County agents and consultants have reported that the flag leaf and penultimate leaf have turned from green to a "gray cast" to brown over the weekend. This can often been seen from the road. Damage in the field has ranged from 15% of the plants damaged to the entire field. Reports have come in from Spring Green, Birnamwood, Coloma, Waupaca county, and Fond du Lac county. Usually the new leaves emerging from the whorl are still green.

Temperatures greater than 100 F can scald corn leaf tissue, especially under environmental conditions of low soil moisture and hot, dry winds. Terminal leaves are first chlorotic, then roll and bleach. Corn hybrids and sweet corn varieties differ in their tolerance to high temperatures.

Will the loss of these upper leaves affect pollination? High temperatures during pollination, may result in poor seed set or sterility. How much effect will there be on grain yield? Kernel number may decrease due to poor seed set and sterility, but kernel weight should remain about the same. Most of the photosynthate that eventually moves into kernels is moved from the stem and from the leaves around the ear. Upper leaves are not as important to final grain yield as the leaves around the ear.

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