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Corn+Soybean Digest

Repel Rootworm

There's a history of southern corn rootworm in central Texas. But with a solid seed treatment program, Creston Voges is making them history.

Voges farms with his brother Boyd a few miles south of Waco in Lorena, TX, a region in the “Blackland” growing area of rich black-clay loam soil. His two-thirds corn and one-third sorghum rotation has battled dreaded drought the past three years. But he still manages to make two-thirds or better of average yields.

Southern corn rootworms (SCR) are among his main insect problems for corn, along with earworms, corn borers, white grubs, wireworms, chinch bugs and occasionally Mexican corn rootworm.

Some YieldGard varieties handle the Mexican type if infestations aren't too heavy, says Roy Parker, Texas AgriLife Extension entomologist out of Corpus Christi, “so caution is in order.” However, for SCR, Voges uses a seed treatment insecticide, usually Poncho.

“It (and other insecticide treatments) protects seed against the early SCR attacks,” he says. He warns that if SCR infestations are apparent in untreated young plants, it's too late.

Also known as the spotted cucumber beetle, the rootworm larvae causes the corn damage. They bore into the stalk just above the roots and kill the growing point of young plants.

When scouting, look for center leaves dying on small plants, dig them up and look for small holes, says Parker. “You have to anticipate this ahead of time,” he adds. “A field's history of infestation and damage is important when deciding whether to use an insecticide for SCR.”

Before using treated seed, Voges depended on granular insecticides applied at planting. The granular applications worked well in his reduced-tillage program.

There are various treatment programs to handle SCR in the South. Insecticides recommended for SCR control include: Lorsban 15G, Furadan 4F (but it loses EPA approval for SCR this year), Counter 20CR, Force 3G and Aztec 2.1G.

Since SCR is a seedling pest, with nearly all of the damage occurring before plants are 6 in. tall, Parker says insecticides don't need to remain active as long as for western and Mexican corn rootworm.

“Granular, liquid and seed treatment insecticides are all effective at about half the rate needed for control of the other two rootworm species,” he says. “However, use the higher rates in fields where heavy infestations occur each year.”

Voges is hoping for a Bt system that will eventually control SCR. He counts on transgenic hybrids for controlling earworms, borers and other bugs. He plants various stacked varieties to handle most of his bug control, even though there's a 50% refuge for corn borer Bt, due to Bt cotton grown in the region, and a 20% refuge for rootworm YieldGard.

“We go with a triple stack (Roundup Ready for weeds, YieldGard and Bt) on 50% of our acres, a Roundup Ready/YieldGard double stack on 30% and straight Roundup Ready varieties on the remaining 20%,” says Voges.

Parker says it's difficult to know exactly where SCR will strike. “If we knew where they would be we would save a lot of money (by lowering overall treatment costs),” he says. “Since we can't control these things once a crop is planted, we have to use preventive treatment. But it's also good for chinch bug and other insect control.”

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