Management of Hessian Fly in the Spring

Joanne Whalen, Extension IPM Specialist; and Gordon Johnson, Extension Ag Agent, Kent Co.;

Last fall, we received a number of calls regarding the need to control Hessian fly in wheat. Although we have not seen or heard of any significant damage from fall infestations, we continue to receive questions about the possibility of problems from the spring population. If stands appear thin and you are checking fields for a reason, you should consider Hessian fly as one of the possible culprits. Volunteer wheat could also be a source of spring infestations. Although the adult fly is not a strong flyer, production fields near volunteer fields that were heavily infested last fall could be at risk for a spring infestation. When the Hessian fly adults emerge from the flaxseed this spring they will seek a host upon which to lay their eggs. Wheat is the principal host plant of the Hessian fly but it may also be found on rye, barley and other wheat-related species.

Although we have not had experience controlling spring infestations with a foliar insecticide, information from North Carolina and Georgia indicated that it can be done but it will not be easy to time applications. Information from North Carolina indicates that if applied timely, Warrior® will provide control. (See link to North Carolina publication).

The following information from Dr. John Van Duyn’s Hessian Fly Management fact sheet provides information on factors to consider when attempting control of a spring infestation with a foliar insecticide.

You must determine when the flies will emerge and begin to lay eggs. If a pyrethroid is applied as the flies emerge and lay eggs, a high level of control may be accomplished. In North Carolina, this occurs in early March; however, we do not have any experience in our area. It will be totally dependent upon weather, particularly temperature.

In this fact sheet, two items are mentioned to help time spring treatments:

  • (1) Look for infested shoots and check for the flaxseed (pupal stage) to determine if a field will have high fly numbers. Squeeze the flaxseed and if they are creamy white it is too early to treat. If they appear orange they are about ready to emerge as adults. An application to a field at increased risk might be warranted. (Warrior label states make an application when adults emerge.)

  • (2) You can also scout fields for eggs which will be very time consuming. Eggs are very small (about half the size of a period), almost translucent, and are laid end to end in a row between leaf veins on the upper surface of wheat leaves. Magnification will probably be needed although someone with experience may be able to see the eggs in direct sunlight. As a general guideline, a treatment may be justified if there are four or more eggs per leaf.

Information modified for Delaware from John Van Duyn’s North Carolina Fact Sheet on Hessian Fly Management) and from “Questions about Spring Populations of Hessian Fly Associated with Infested Volunteer Wheat” By Doug Johnson in the February 11, 2008 issue of the Kentucky Pest News from the University of Kentucky College of Agriculture.

NOTE- Hessian Fly Alert in North and South Carolina – This new information was received from Ames Herbert in VA the afternoon of Feb 28 regarding high levels of Hessian fly in wheat in North and South Carolina. Information provided by Dr. John Van Duyn in North Carolina indicates that, in general, infested fields have been characterized by one or more factors: 1) planted with HF susceptible wheat variety 2) planted without Gaucho or Cruiser seed treatment 3) planted wheat after wheat, especially no-till 4) seedlings emerged before November 5) wheat planted close to the last wheat crop. Although we have not had reports from Delaware, if these situations fit any of your wheat fields, be sure to go to the following link for new information on timing treatments (

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