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College of Food, Agricultural, and Environmental Sciences


Unusually Cool Summer Temps Slowing Corn Development

July 23, 2009

COLUMBUS, Ohio – Cooler-than-normal summer temperatures are slowing corn development across Ohio, and harvest could be delayed if the weather trend continues throughout the growing season.

Peter Thomison, an Ohio State University Extension agronomist, said that corn planted in late April or early May would normally be tasseling and silking by now, but because of the cooler temperatures, many cornfields have not reached these growth stages yet.

"We haven't seen much silking yet, and in some areas, the corn is shorter than normal. What we are looking at here is the cool weather causing the slow development and shorter plant height," said Thomison, who also holds an appointment with the Ohio Agricultural Research and Development Center. "When you have cool weather, cells don't grow as big so internodes are shorter and plants are shorter in height. Lack of soil moisture is also contributing to smaller plants in areas short on rain."

According to the Ohio Agricultural Statistics Service, 33 percent of the corn crop is silking, slightly higher than last year at this time, but behind the five-year average by 17 percent. As of July 19, there were 119 growing degree days, 47 days below normal.

In addition to the cooler temperatures, lack of adequate rainfall in some areas of the state is also impacting the crop. But things could be worse, said Thomison.

"We are seeing tremendous variation across the state. Those areas in the state that have been getting rain, combined with moderate temperatures, have ideal growing conditions for corn," said Thomison. "In areas lacking rain, the low temperatures are helping limit water stress. Otherwise we would probably be confronted with major drought damage from the lack of rain we'd be experiencing."

Cool temperatures have benefits for the corn crop during the upcoming grain-fill period. Thomison said that cooler temperatures slow respiration, contributing to better grain fill, a lengthier grain fill period and potential higher yields. Cooler temperatures also inhibit disease and insect development.

Cooler temperatures throughout the growing season could delay harvest, however.

"The situation reminds many of the corn crop in 1992, when we had phenomenal yields, but we also had corn harvested in January because it was too wet during the fall to enter the fields," said Thomison. In that year, average state corn yield was 143 bushels per acre, the highest acreage recorded to date at that time.

Despite the cooler temperatures, the crop still needs adequate moisture. According to the Ohio Agricultural Statistics Service, as of July 19, rainfall averaged 0.27 inches, 0.53 inches below normal. Topsoil moisture was rated 58 percent short to very short.

"Right now farmers are looking at when the next rain is coming," said Thomison. "Despite the current rains we've had over the last day or two, we still need more."

According to the Ohio Agricultural Statistics Service, corn is 74 percent in good to excellent condition.

For the latest crop updates, refer to the OSU Extension Agronomic Crops Team Web site at

Corn is Ohio's most valuable field crop commodity. According to the Ohio Department of Agriculture, corn production contributes $2.1 billion to agriculture. Feed grain serves as a main component of corn production, but the crop is also becoming an integral source for ethanol.

Candace Pollock
Peter Thomison