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College of Food, Agricultural, and Environmental Sciences


Drought-Stressed Corn Struggling to Produce a Crop

July 26, 2002

COLUMBUS, Ohio - Hit-and-miss rain showers that have been recently soaking parts of Ohio may not be enough to relieve the corn crop's drought stress, ultimately resulting in significant yield losses.

"We need a good frontal system to sit over the state and dump rain for about two or three days, and then weekly rains for the remainder of the growing season. These scattered showers are just not going to cut it," said Peter Thomison, an Ohio State University Extension agronomist.

Thomison, who is also a researcher with the university's Ohio Agricultural Research and Development Center, said that dry conditions combined with a marginal root system created by a cool, rainy spring is resulting in poor crop performance during pollination - a critical time of development for yield potential.

"Many corn fields throughout Ohio are either already there or entering the stage of pollination, which is the most critical period of the corn plant's development," said Thomison. "The corn that is near flowering is suffering because of the effect drought has on the pollination process." Thomison said that dry conditions can delay silking, resulting in poor synchronization of silking and pollen shedding that, under normal conditions, fertilize the kernels and fill the ears of corn with grain. Delayed silking may result in a reduced kernel set, where only the ears are partially filled. According to the Ohio Agricultural Statistics Service, 20 percent of the state's corn is silking, a week behind normal development.

"Delayed silking can have an extreme impact on yields. Four consecutive days of drought can reduce grain yields as much as 40-50 percent," said Thomison. "And unfortunately, there are many fields that have surpassed that." Poor root development is also complicating the drought-stressed situation.

"Corn plants generally grow roots in the top three feet of the soil layer and if growing under favorable conditions, they can tap moisture in that top three feet and survive during periods of drought much better than if they were confined to the top couple of inches of soil, which is the situation we are finding in many fields this year," said Thomison.

In addition, the leaf canopy for many corn plants has not closed, leaving big gaps within and between cornrows and shooting soil temperatures up into the 90s. "The roots of many plants are just baking," said Thomison. "There is no canopy to shade them from the heat so many roots near the surface are desiccated and probably, in many cases, dead." Some of the most noticeable symptoms of extreme drought stress are tightly rolled corn leaves and reduction in plant height. Thomison said many plants, which should be at least seven to eight feet tall, are only half that size.

"Severe drought conditions have just basically caused the plants to shut down," he said.

Add insect pressure to the mix and many farmers may be giving up on their corn crop all together this year.

Ohio State Extension specialists have been receiving reports of silk clipping from rootworm beetles and Japanese beetles, which is exacerbating pollination problems.

"If the corn was actively growing, it'd probably outgrow these insect problems. The beetles are clipping off the silks and feeding on the pollen, so there are no silks to pollinate," said Thomison. "For many farmers, insect pressure is another nail in the coffin." Ohio State entomologists recommend farmers first determine whether or not the corn has pollinated before administering any treatment. If pollination has occurred, silk clipping will not affect yield.

Treatment to control rootworm beetles is warranted if five or more beetles are found per silk mass when 75 percent of the plants have silked and silk clipping is less than a quarter of an inch. Treatment for Japanese beetle is warranted when there are three or more beetles per silk mass.

Thomison said that farmers shouldn't jump the gun just yet in coming up with other options to salvage their crop for uses other than grain. An immediate dousing of long-term, statewide rain showers could help resurrect the crop and produce some decent grain yields given the conditions farmers have been faced with.

"We went through the same situation in 1988 where it was dry until the end of July and then we just got a lot of rain. It produced a fairly decent crop given the stress conditions the crop was experiencing," said Thomison. "If we get good rain at this stage and the remainder of the growing season, we might be able to salvage the crop." Thomison added, however, that despite the relief long-term rains would provide, yields might still be markedly below average.

Candace Pollock
Peter Thomison