Maximum corn yield potential across most major corn-producing states has been nipped in the ear by the hot and dry weather "bullet" – especially on corn that's silking. This is the most critical period for grain yield determination, points out Peter Thomison, Extension corn agronomist at Ohio State University.

According to the National Ag Statistics Service July 2 reports, top soils in corn fields from Nebraska to Pennsylvania ranged from 45% to 89% moisture-short during the last week. Those percentages dropped substantially in New York and New England.

NOT A GOOD SIGN: Corn leaf-rolling throughout much of the day during silking may be a sign you need to reduce your harvest yield expectations.

But recent crop stress already may have eliminated some extra kernel rows, suggests Greg Roth, Extension corn agronomist at Penn State. "I don't think kernel development has been hurt too much yet on [Pennsylvania's] better soils," he speculates. "However, if the combination of drought and heat continues on some fields for the next week or so, then pollination will be impacted and kernel set will be reduced considerably." 

Thomison reports Iowa State University studies have found that just four days of moisture stress has potential of reducing yields by 5% to 10% when corn is at the 12- to 14-leaf stage (chest high). During tassel emergence, four days of moisture stress can reduce yields 10% to 25%. Four days of extensive leaf-rolling moisture stress by mid-day on silking corn may increase those potential yield losses to 40 to 50%.

Next 10 days critical

Roth thinks many fields still have a good yield potential. "But I would expect pollination to drop along with yields if heat and drought continue for the next 10 days. Accuweather seems to be calling for a wet period in mid-July for the East. That would really favor the later planted corn.

To check the long-term outlook for your area, go to www.accuweather.com . Type in a city near you, and click on the "month" tab.