Corn Reproduction and High Temperatures

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu, Cory Whaley, Extension Agent – Agriculture, Sussex County; whaley@udel.edu, and Phillip Sylvester, Extension Agent – Agriculture, Kent County; philllip@udel.edu

Droughty conditions aren’t our only worry right now. Corn that survived the deluge of rain is tasseling in our earliest planted fields, and our current heat index can be an issue with pollination. While corn enjoys warmer weather, anything above 86°F will actually slow plant growth. A corn plant also prefers cooler nights, with temperatures in the 60s.

Pollination occurs during tasseling and silking stages, and high temperatures can adversely affect kernel formation either during pollination or grain fill. First of all, warmer weather this week may accelerate corn maturity earlier than we would like. High daytime temperatures (> 86°F) may limit photosynthesis which provides sugars for ear formation. A survey of worldwide research on corn growth and temperatures observed that the ideal temperature for growth as well as flowering was 86-87°F. Temperatures over 99°F severely affect pollen production during silking, but consecutive days in the 90s will at least reduce pollination. For grain fill, optimum temperatures are 80°F, with a maximum of 97°F. In the mid-west, high night-time temperatures (>72°F) have been observed to reduce grain fill, possibly due to the use sugars for respiration (energy) rather than kernel production.

This photo from last year shows a worst-case scenario when temperatures are high, with many kernels failing to pollinate. In most fields, it may just be a few kernels per ear that fail, but over several acres that can add up.

Over the week of June 28-July 4, when tasseling started in some fields, we have had temperatures at least 86°F, with four to six days in the 90s (Table 1). New Castle has seen two nights above 72°F, while both Kent and Sussex have had three. As of writing this, cooler days and nights are in the forecast, as more of our earlier planted fields will start pollination. That is good news for most fields that are just getting started, but for all the late-planted corn and replants, watch the temperatures in mid and late July. Temperature may be an additional factor to consider if this year’s yields are lower than expected.

Table 1: Number of days above threshold temperatures over the week of June 28-July 4