Arkansas

The summer has been hard on Arkansas crops. They've been severely stressed by heat and drought. But they've also been stressed by an unseen enemy, nematodes.

Nematodes are microscopic organisms that feed on the roots of cotton, soybeans and corn.

"Nematodes cause considerable root damage, which adds to the stress crops have endured this summer," said Dr. Terry Kirkpatrick, plant pathologist for the University of Arkansas Cooperative Extension Service at the Southwest Research and Extension Center at Hope.

"Even in good years, nematodes cost farmers yield. Depending on the field, crop and cropping history, cotton yield losses can range from 50 to 200 pounds per acre, and soybean losses can range from a few bushels an acre to about a third of the crop."

Kirkpatrick said farmers can readily see weak spots caused by nematodes in their fields in a year like this. They should note these areas and return in the fall for samples.

Three major types of nematodes are scattered across Arkansas.

"In cotton, the root-knot nematode is in every county where cotton is grown. Hot spots are in areas of eastern Arkansas where soils are sandier," Kirkpatrick said.

Reniform nematodes affect cotton yield in 12 counties, but they're most widespread in Monroe County.

The soybean cyst nematode is still the No. 1 threat in soybeans. It's found everywhere soybeans are grown.

"Root-knot and reniform nematodes are beginning to become more prevalent in soybeans and were especially noticeable this year," Kirkpatrick said. "There's dramatic damage to soybeans in southeast Arkansas, in some fields in the Arkansas River Valley, and in northeastern Arkansas from root-knot nematodes. Meanwhile, it's conservatively estimated that reniform nematodes are causing a 10-bushel loss in soybeans in the 12 counties where they occur."

Root-knot nematodes "love" corn, Kirkpatrick said, and some of the highest populations occur after a year of corn. If you grow corn, he said, you may have increased the problem for the next crop.

In cotton, farmers have three choices of nematicides. Telone II can be applied in the fall before planting in a minimum-till situation, or in the spring two weeks before planting.

"Telone II is expensive and requires special equipment to inject it into soil, but it's the most effective nematicide," Kirkpatrick said. "It should be reserved for top-end fields with high yield potential where production has dropped off.

"Our research over the last five years indicates a lint increase of about 175 pounds an acre with Telone II in severe problem fields."

Another option is Temik, a granular product. Temik has been the standard for Arkansas growers for several years. It's applied at planting in the furrow with the seed, and suppresses nematodes and early season insects at half the cost of Telone II.

"Our research indicates an improvement of about 75 pounds of lint per acre with Temik applied at five pounds an acre in the furrow and about 100 to 120 pounds an acre yield improvement with five pounds in the furrow followed by an additional five pounds an acre sidedressed at pinhead square," Kirkpatrick says.

"A new material this year is Avicta, a commercially-applied seed treatment. It's a combination of nematicide, an insecticide for thrips, and fungicide for seedling diseases. Avicta will be convenient. Just dump it in the hopper and plant it. It'll perform about the same as Temik at five pounds per acre in-furrow."

In corn and soybeans, no nematicides are recommended. Nematodes have to be managed by either variety selection or crop rotation in soybeans or crop rotation in corn.

For more information about crop pests, contact your county Extension agent or visit Extension's website at www.uaex.edu. The Cooperative Extension Service is part of the U of A Division of Agriculture.

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Date: 9/22/05

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