Pollination is a critical period for corn development and yield. 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 no longer viable once temperatures reach the mid 90's 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, thereby reducing seed set if pollen is no longer available. The amount of pollen from one plant is sufficient for ten plants; this 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 pollination if soil moisture is adequate. Drought stress along with high temperatures at pollination and silking though can have serious effects. If dry-hot conditions continue over the pollination window, expect to see major differences among fields based on management practices and hybrids. Practices that conserve soil moisture such as no-till or reduced till will improve a crop's performance during drought. It is possible that early-season hybrids could do better than other hybrids if pollination occurs before temperatures soar or moisture reserves are depleted. Using a hybrid though that has overall good stress tolerance is most important overall, because it is impossible to predict when stressful conditions will occur year to year.
Portions of this text, written by Roger Elmore, are taken from a Crop Watch article (University of Nebraska extension newsletter) published June 15, 2005.
For more information, see the following articles written by Bob Nielsen of Purdue University.