What is in this article?:
- Beware of pest problems in wheat following wheat
- Burying stubble slows fly emergence
• Among the problems usually found where wheat follows wheat are the insect pest Hessian fly and diseases problems such as take-all and Fusarium head blight.
Increased wheat production in the past couple of years in the Southeast has brought with it a few pest problems that commonly can be found wherever wheat follows wheat in a farmer’s field.
Among these problems are the insect pest Hessian fly and diseases problems such as take-all and Fusarium head blight.
“There are insects that can over-summer in wheat fields, so if you grow wheat after wheat, you can run into certain problems,” says Kathy Flanders, Auburn University Extension entomologist.
“So crop rotation is always much better when growing wheat. It’s always better to grow wheat every other year. If you don’t follow a good rotation, the main insect pest is Hessian fly, and it helps to know what it is doing right now.”
Right now, says Flanders, Hessian fly is hanging out in the wheat crop from earlier this year, in the stubble and the top areas of the soil. “They are pupae that are about to hatch out as the first generation of Hessian fly.
“They’ll lay eggs on volunteer wheat, build their populations and be ready to lay eggs in your wheat crop. They over-winter in the previous year’s wheat fields, so if you plant wheat after wheat, you’re just making it easy for them,” she says.
The Hessian fly caused disastrous losses in Alabama wheat in the mid-1980s, says Flanders. In 1985, estimated losses were 21 bushels per infested acre. Since that time, later planting of wheat and the use of wheat varieties resistant to Hessian fly have minimized economic losses to this pest.
In coming years, however, entomologists expect the risk of economic losses from Hessian fly to be as high, or higher, than they were in the 1980s, she says.
Reasons for this include increased wheat acreage, supply shortages of Hessian fly-resistant wheat varieties, widespread occurrence of a strain of Hessian fly that overcomes resistance in most wheat varieties, increased conservation-tillage, and disrupted crop rotation schemes as farmers plant the crop that offers the best promise for an economic return.
A last and very important factor, says Flanders, is that phorate and di-syston insecticides no longer are used at planting to control Hessian flies.
“Historically, Hessian fly has caused the greatest problems in the southern two-thirds of Alabama,” she says.
There are four to six generations per year of this pest in the South, says Flanders. The entire life cycle requires about 35 days at 70 degrees F., longer at cool temperatures. Generations tend to overlap.
“The pest over-summers as flaxseeds in wheat stubble. The first generation in September is generally on volunteer wheat or on wild grass hosts, the most important of which is little barley. Then there are often two more generations in the fall and early winter,” she says.
Feeding by Hessian fly maggots permanently stunts vegetative tillers and can kill seedlings. If fall-infested tillers do produce grain heads, these heads are small and the stems are stunted.
Spring-infested plants have weakened stalks, which can lead to stem breakage and lodging. These plants also have poorly filled, smaller grain heads. Hessian fly reduces forage production of winter wheat, but does not greatly affect wheat forage quality.
The most reliable Hessian fly management strategy in the South is to plant varieties of wheat that are resistant to Hessian fly, says Flanders. Rye or oats may be a better choice for grazing as they are poor or non-hosts for Hessian fly, she says.