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Seed Treatment Being Developed For Corn Borers; Still 2 Years Away

August 21, 1988

DES MOINES, Iowa (AP) _ Agricultural researchers in Iowa are reporting some success in using seeds pretreated with an insecticide to fight European corn borers, pests the government estimates cost U.S. farmers $400 million a year in damage and control expenses.

Pretreating seeds with a thiodicarb solution before planting has been found as effective in controlling corn borers as any spray now on the market, yet is more economical and appears to be safer to the environment, said Edwin C. Berry of the U.S. Department of Agriculture’s Corn Insects Lab in Ankeny.

But the process isn’t ready for farm use yet.

Berry said the treatment is in its third year of tests and that another year of research is planned.

″We’re interested in learning why it is effective in some hybrids and not in others,″ he said.

Berry also said researchers want to know if the mechanical action of mixing the seeds with the chemical solution affects seed quality or influences the action of insecticides.

In addition, the chemical seed treatment has yet to be approved for commercial use by the Environmental Protection Agency and its Des Moines developer, Gustafson Inc., says the process is still two years away from the marketplace.

Researchers also have been experimenting with natural controls of corn borers through the interaction of an insect, the green lacewing; and a microbe, Nosema pyrausta.

The lacewing eats corn borer eggs and larvae, and the microorganism infects larvae and borer eggs with a disease that is fatal to the borer and most other insects, but not the lacewing, according to the USDA.

″Because most insecticides that kill the corn borer indirectly kill the microorganism, researchers will try next to determine how farmers can maintain natural Nosema pyrausta populations with tilling practices, crop management and less pesticide,″ the Agricultural Research Service reports.

In the seed treatment, seeds are mechanically tumbled in a solution of the insecticide thiodicarb before planting.

As the corn grows, the chemical is absorbed throughout the plant’s stalks and leaves and the insect feeding on the plant dies, Berry says.

Corn borers cause their crop damage in their worm or larvae stage before maturing to adult moths. There are two to three generations to each growing season, according to Berry.

The larvae enters the plant and causes damage by eating through conductive tissues, interrupting the flow of nutrients. If it enters a corn stalk or ear, it weakens the plant and makes it susceptible to wind damage.

Because the insect is on the plant’s surface for only a short period of time before tunneling, it is especially difficult to combat with a spray, says Berry.

″This is why a systematic or seed treatment is so encouraging,″ he says.

Thiodicarb already is being used as a corn rootworm insecticide that is sprayed just before insect infestation, and Berry said it was routinely evaluated as part of research attempts to find materials that are environmentally safer and more effective.

Through early tests, researchers found the lowest concentrations of chemicals that proved effective against corn borers.

″Depending on the strain of corn, we can achieve as good a control with seed treatment as with conventional technology and it is more economical,″ Berry said, controlling 70 percent to 80 percent of the insect population. He also said the seed treatment puts less pesticide in the environment and has no known side effects.

In spraying, 80 percent of the insecticide misses the target area, he said.

Ray Knake, northern regional manager for research and development for Gustafson, said his company is developing the chemical for seed treatment use for the international company Rhone-Poulenc, which is registering such use of thiodicarb with the EPA.

He estimated the treatment would cost farmers a couple of dollars an acre.

Knake said a simple mixer is being developed for farm use so that farmers need not come in contact with the chemical while treating seeds. He says the chemical breaks down so rapidly in the soil that it is environmentally safe.

While many details need to be worked out, Gustafson anticipates selling the insecticide for on-farm treatment, leaving it up to farmers to decide how much of their seed to treat and saving seed companies from investing in large stocks of treated seeds, Knake says.

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