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ISU: Storms may have cut corn yields substantially

By Staff | Jul 29, 2011

Ryan Risdal, manager of Centrol of Iowa, in Nevada, a division of Key Cooperative, displays a damaged corn plant from high winds earlier this month. He estimated that a combination of the winds, coupled with the recent high temperatures, could cut the area’s corn yield from 5 to 30 percent.

By KEN BLACK

For Farm News

MARSHALLTOWN – Preliminary estimates are that corn harvest yields from the July 11 windstorm may be reduced anywhere from 5 to 30 percent in affected fields, representatives from Iowa State University said last week.

However, even with the strong winds that buffeted the corn, all is not a total loss, said Mark Licht, an ISU field agronomist.

“A lot of the upper parts of the plants have uprighted,” he said.

That should help during pollination, which Licht said experts at the university are anticipating in many fields, despite the damage done. However, that pollination and ear production will depend on one main factor: whether the corn was simply bent, or lodged, or whether there was green snap, or breakage of the tissue that supports the plant.

Of course, the winds last week are now only part of the problem. The corn is now also experiencing a great deal of heat stress, Licht said.

If temperatures stay higher than 93 degrees for four straight days, that could lead to yield loss of 1 percent. If they stay that hot for six days, yield loss could be as high as 4 percent.

“Above six days, we really have no clue,” he said. “We are going to have a least six days, maybe 10 days, where temperatures are that high.”

In addition to the daytime temperatures, even temperatures overnight can cause some problems.

“Pollination is a concern but I’m concerned about higher overnight temperatures that don’t give the plants the chance to shut down and get ready for the next day,” said Ryan Risdal, manager of Centrol of Iowa in Nevada, a division of Key Cooperative.

Temperatures and the stress the corn is already under also plays a role with a variety of pathogens as well.

Alison Robertson, a plant pathologist at Iowa State University, said that while the warmer temperatures will keep some of the most common diseases in the state down, gray leaf spot is a concern.

“Gray leaf spot likes warmer temperatures,” she said.

That disease has the ability to totally wipe out a crop, if left untreated. Robertson said farmers should monitor their fields and take action if gray leaf spot is found. A fungicide is often used to control outbreaks.

With the corn being damaged, Robertson said stalk rot is also a concern. Farmers need to monitor and do field tests for stalk rot.

“If there is more than 10 to 15 percent of the corn having stalk rot in the fields, you must schedule that corn for an early harvest,” she said.

None of the farmers at the meeting were particularly concerned about the ability to find storage after the harvest. Mid-Iowa Coop had a representative at the meeting who said farmers who used elevators in locations such as Green Mountain and Garwin would soon be receiving information about an upcoming meeting to discuss the coop’s plan for the fall.

Contact Ken Black at kblack@timesrepublican.com.

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