The 2011 wheat crop will be one of the most valuable on record when it’s harvested later this spring.

Protecting the crop from Hessian flies is an ongoing battle for growers in the upper Southeast and the fight is going to get tougher.

Many of the varieties that contain genes that make wheat resistant to Hessian flies and/or Hessian fly damage are not working in the Southeast. The U.S. Department of Agriculture contends care should be taken to ensure resistance genes not currently used in commercial wheat varieties be used prudently.

Wheat resistance genes recognize a virulent Hessian fly and activate a defensive response that kills the fly larvae attacking the plant. However, this leads to strains of the fly that can overcome resistant wheat, much like insects becoming resistant to pesticides.

In the Southeast there are multiple generations of Hessian fly during the growing season, which increases the odds of that these flies can overcome wheat’s resistance.

USDA analysis of wheat lines carrying resistance genes from dozens of locations throughout the Southeast showed that some give little or no resistance to the Hessian fly. Others, even those considered the most effective, are allowing wheat to become susceptible to the fly larvae, which feed on and kill the plants.

While the study did not include all of the 33 named resistance genes, it did show that only five of the 21 genes evaluated would provide effective resistance to flies in the Southeast, and none was effective in all the Southeast locations.

In the Southeast, it was particularly troublesome that some of the newer genes that haven't been deployed in cultivars weren't too effective in protecting wheat from Hessian flies.

USDA researcher Brandi Schemerhorn says it's possible that some of the genes were introduced to flies unintentionally in plots where wheat cultivars with those genes were being tested for suitability to Southeast climates. The resistance genes also could have come from other plants, such as rye, and the flies may already have started to overcome those genes.