Farm Talk

April 1, 2014

Bt-resistant rootworms ID’d in five states


Associated Press

Parsons, KS — Researchers say bugs are developing resistance to the widely popular genetically engineered corn plants that make their own insecticide, so farmers may have to make changes.

Cases of rootworms eating roots of so-called Bt corn have been confirmed in Nebraska, Iowa, Illinois, South Dakota and Minnesota.

Iowa State University researchers found that rootworms have developed resistance to two of the four genetic traits in corn plants that are engineered to kill rootworms. Iowa State professor Aaron Gassmann said the problem isn't widespread yet, but farmers and seed companies should consider changing their approaches to pest control.

``Hopefully, people can learn from these cases of resistance,'' Gassmann said.

The popular corn variety gets its name from the insect-killing bacterium it contains, bacillus thuringiensis, a natural insecticide that is considered harmless to people and livestock. The U.S. Department of Agriculture reports that 76 percent of all corn planted last year was Bt corn.

When rootworms attack, clumps of corn plants can be leveled by summer storms because they don't have the roots to anchor them.

In areas where Bt corn has failed to control rootworms, farmers often turn to insecticides.

Researchers believe that rootworms are more likely to develop resistance to Bt corn when farmers plant the same hybrid in a field year after year, said Lance Meinke, an entomologist at the University of Nebraska-Lincoln.

Most farmers rotate corn with other crops in a practice long used to curb the spread of pests, but some abandoned rotation to cash in on corn prices that stayed high for several years or because they needed more grain for livestock.

But even with crop rotation, the beetles may be finding a way to thrive. Researchers are investigating reports that some corn rootworms in central Illinois found a way around crop rotation by laying eggs in soybean fields.

The problem of resistant rootworms could easily spread because the larvae grow into adult beetles that can fly to new areas.

Meinke said farmers should think of Bt corn as just one part of their strategy for managing rootworms. He said it doesn't appear likely that seed companies will be able to make significant improvements in the corn hybrids in the next few years.

``Right now there is nothing on the horizon for the next four or five years that is going to come out. So we have to manage rootworms with what we have,'' Meinke said.