ALABAMA A&M and AUBURN UNIVERSITIES

Plant Breeders Scurry to Keep Up with Hessian Fly

AUBURN, SEPT. 24---They’ve been here for more than two centuries and are likely to be around at least a couple more. But if U.S. Department of Agriculture (USDA) researchers and Extension specialists any say in the matter,they won’t be threatening wheat as they have in the past.

The Hessian fly, which experts believe was brought to the United States in the bedding of British mercenaries during the American Revolutionary War, remains a serious wheat pest.

Within the last few decades, however, plant breeders have had stunning success developing wheat varieties resistant to the fly. Still, some of the flies have managed to overcome resistance no matter what.

"Selection pressure tends to be so strong with the few that survive that they evolve into new biotypes – groupings of flies that share the same genetic traits," says Dr. Kathy Flanders, an Alabama Cooperative Extension specialist who is involved in efforts to control the fly in North Alabama wheat.

One particular type, known as "L," by developing resistance to every variety currently available to growers, has presented breeders with a special challenge, Flanders says.

In North Alabama, Biotype-L makes up a great proportion of Hessian flies, making the region especially prone to damage from the pest.

Nevertheless, breeders aren’t ready to throw in the towel. Already they're developing a new line of resistant varieties that soon will be commercially available in the deep South.

In addition to planting resistant varieties, Flanders says wheat producers are urged to follow a couple of other practices.

"There are a lot of things that encourage Hessian flies," she says. "Before the development of resistant varieties, growers still were able to turn out a good wheat yield so long as the crop was carefully managed. For example, if you plant wheat too early, continually on the same cropland, or on no-till cropland, you risk a buildup of the flies. This is because the flies can 'oversummer' in wheat stubble," Flanders says.

The bottom line is that in areas where resistant varieties don’t work, producers should plant wheat as late as possible without sacrificing their yield potential. Also, planting wheat on the same cropland season after season is risky, especially in areas where voluntary wheat is prevalent.

One common way in which Midwestern producers deal with this risk is to plant after "fly-free" dates.

"We know the flies stop developing after a certain date when the weather becomes too cold," Flander says. "So, by planting after this fly-free date, producers are able to reduce the risk of infestation."

Unfortunately in the warmer Southern climates, it’s harder to predict when this rapid cool-down date will occur.

The Hessian fly attacks wheat first by laying eggs on plant leaves. After emerging from their eggs, the larvae make their way into the sheath, which is the part of the leaf attached to the plant stem, and begin growing by feeding on the plant’s sap.

The saliva of these larvae is very toxic to wheat plants and the end result is a plant that ultimately dies or becomes seriously stunted.

Two hundred years ago, Hessian flies were as unwelcome to these shores as the British mercenaries who brought them. However, with the release of these new resistant varieties, Flanders believes producers finally will gain the upper hand over an insect that has pestered them for generations.

SOURCE; DR. KATHY FLANDERS, Extension entomologist with the Alabama Cooperative Extension System, (334) 844-6393.