Fly-free dates for wheat

The Hessian fly is a potential pest of our wheat crop, although it has not caused serious losses in recent years. The Hessian fly spends the summer in a resting stage (the pupa, commonly called a flaxseed for this insect). Adult flies emerge in the fall to lay eggs on volunteer and early-planted wheat. Larvae feed inside the plant, stunting and reducing yields. High humidity is necessary for a significant infestation to develop. Therefore, injury is often more severe during years of abundant rainfall. Injury can occur either in the fall or spring. Once a field becomes infested, no chemical control measures will stop the injury. Control is based entirely upon prevention and depends on good crop management. Three cultural practices are recommended to reduce or avoid Hessian fly problems.

  1. Destroy volunteer wheat. Allowing volunteer wheat to grow for two to three weeks, especially during a wet summer, encourages development of a larger fly population. That population then can carry over into the regular crop planting. Volunteer wheat allows the population to increase and makes planting after the fly-free date less effective. Destroying volunteer wheat by mid-September prevents flies from finding hosts and helps reduce the overwintering population that might spread to nearby fields in the spring. Hessian flies sometimes use barley and rye as hosts, but not oats.
  2. Plant a resistant wheat variety. Kansas State University entomologists recommend planting resistant wheat varieties to reduce Hessian fly problems. Annual evaluations of Kansas wheat varieties have found several with resistance to Hessian flies. These include Arkan, Brule, Caldwell (soft), Clark (soft) Compton (soft), Hart, Larned, Norkan, Pike, Pioneer 2157, Pioneer 2163, Pioneer 2172, Pioneer 2180, Pioneer 2551 (soft), and Redland. University of Illinois entomologists list several other varieties that have fly resistance: Auburn, Fillmore, Arthur 71, Abe, Sullivan, and Beau.
  3. Plant after the fly-free date. The dates shown on the map are based on historical data that suggest when most of the adult flies will have emerged and died. However, cool, moist weather during September may cause the average fly emergence date to be earlier this year. If so, very few flies will be around to attack fields planted after the fly-free date.

This article originally appeared on pages 161-162 of the IC-476(23) -- September 3, 1996 issue.

Updated 09/02/1996 - 1:00pm