How high temperatures, stress affect corn pollination

As of Sunday, July 16, the National Agricultural Statistics Service (NASS) Nebraska Field Office reported that 60% of the state’s corn crop had silked. This was considerably ahead of the five-year average of 14% and last year at 16%.

Silking and pollination . . . are critical to the corn crop’s viability and yield, but unlike pests and weeds, are something you can’t control. If you’re a little hazy on the details or need a refresher, don’t blush. Bob Nielsen, an agronomist at Purdue University, has written three articles which illustrate the process. The articles are available on his site, the Chat ‘n Chew Café and found under the posting date, July 11. The articles include Sex in the Cornfield: Silk Emergence, Sex in the Cornfield: Tassel Emergence and Pollen Shed and Suggestive Behavior in the Corn Field: A Fast and Accurate Pregnancy Test for Corn.

To address this question, we are republishing the following article, originally published in the July 13, 2001 CropWatch, on pollen viability and silk receptivity.

Pollination is a critical period for corn development and yield. The following summarizes information from various sources on how this stress affects corn at this critical stage.

Pollen shed occurs over a two-week period. For kernels to develop, silks must emerge and be fertilized by viable pollen. Silks grow about 1 to 1.5 inches a day and will continue to elongate until fertilized. Temperatures greater than 95°F with low relative humidity will desiccate exposed silks but not impact silk elongation rates greatly. Pollen is killed by temperatures in the mid 90s or greater, especially with low relative humidity. Fortunately, pollen shed usually occurs from early to mid-morning when temperatures are lower.

Drought stress slows silk elongation but accelerates pollen shed. This can result in pollen shed occurring before silk emergence. Any stress such as inadequate water, low soil fertility, or too thick of a planting rate can delay silking two or more weeks and reduce seed set if pollen is not available. This is potentially a major problem although I have not heard of it happening often. The fact that pollen from one plant in ten is sufficient to pollinate a field provides a degree of compensation and improves the opportunity for fertilization in stressful environments.

The bottom line is that high temperatures will not severely stress corn if soil moisture is adequate. Reports of subsoil moisture across the state indicate that levels are varying widely, with some sites reporting their lowest of the growing season and others reporting two to four inches of moisture in the top two feet. Obviously we don’t have to tell farmers to keep up with irrigation at this time of year. It is one of the best ways to reduce the impacts of high temperatures on corn pollination and fertilization.

Rain-fed fields are more of a concern. Drought stress with high temperatures at pollination and silking can have serious effects. If the current dry-hot conditions continue, I would expect to see major differences among fields based on management practices and hybrids. Practices that conserved soil moisture this spring or last year such as no-till or reduced till will improve a crop’s performance during drought. Early season hybrids probably will do better than other hybrids if pollination occurred before temperatures soared or moisture reserves were depleted. Full-season hybrids with good stress tolerance may do better than others with less stress tolerance.

Roger Elmore
Former UNL Extension Crops Specialist

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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