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Memory one tool against pests

MISSISSIPPI STATE, Miss. — A cotton grower's best defense against insect pests may be a long memory. Mike Williams, entomologist with Mississippi State University's Extension Service, has monitored insect battles for many years across the Cotton Belt and especially in Mississippi. He is familiar with the weapons in growers' arsenals: transgenic cotton, insecticides, application timing and alternative crops. But he believes the most important weapon may be a grower's memory of past challenges in certain fields.

"In 2002, cotton's biggest insect threat came from bollworms and budworms. Mississippi growers treated for them in more than 1 million acres and still lost 111,250 cotton bales," Williams said. "Farmers need to remember where worms have been problems in the past and keep that land in Bt (worm-resistant) cotton."

In addition to remembering the history of the land, Williams encouraged farmers to keep in mind the weather conditions that likely influenced insects.

"Just as the weather affects plant growth, it is also tied closely to insect numbers. Remember the weather scenarios, and when conditions are similar to years when insects were a significant problem, be prepared for trouble again," Williams said.

Last year, Mississippi farmers planted 1.18 million acres in cotton. They were unable to harvest about 10,000 acres, largely due to heavy, late-season rains.

"Mississippi would have had record-breaking yields if not for the rains at harvest," Williams said. "We also lost just under 5 percent of the crop to insects, which is about normal. Some years we may lose 10 to 15 percent, and that is excessive, indicating that we didn't use our tools correctly."

The state's second greatest insect losses in 2002 came from plant bugs, which stole about 80,500 bales of cotton from Mississippi fields. They were also the most expensive pest to try to control at $19.17 per acre compared to $15.21 for bollworms and budworms.

"Spraying for plant bugs may have hurt some beneficial insects that would have controlled the worms," Williams said. "Even in the Bt cotton, some growers were quick to spray when they saw worms, but worms have to take a bite out of the Bt for it to work properly."

Williams said growers are in the process of deciding which fields to plant in transgenic cotton. Only available since 1996, Bt cotton acreage has trended down nationally since it peaked in 2000. Part of the reason for the decline may be growers' short memories of previous worm damage.

"Growers have to pay extra ($20.60 per acre) for Bt seed, so when memories of previous losses to worms fade, farmers may take the chance with non-Bt varieties. If the field didn't have a history of major worm problems, it might work out fine," Williams said. "There has been research into the risk of worm resistance to Bt. Resistance is a threat anytime growers are excessive in their insect control efforts."

Other insects responsible for Mississippi yield losses include thrips (14,780 bales), stink bugs (12,281 bales) and fall armyworms (6,028 bales). Smaller losses are attributed to aphids, spider mites, loopers and cutworms.

Linda Breazeale writes for MSU Ag Communications.

TAGS: Management
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