hessian fly

female Hessian fly.

With silage harvest progressing, many farmers in Pennsylvania are turning, or have turned, their attention to establishing small grains. With fall-established small grains, Extension Entomologist John Tooker explains it is wise to be aware of the risk from the Hessian fly.

While many Pennsylvania growers have never encountered Hessian flies, the past decade has seen an increasing number of outbreaks in eastern states, including Delaware, Virginia, and North and South Carolina. This pest is most problematic in wheat, but will also attack barley and, to a lesser extent, cereal rye, which tends to have good resistance against Hessian fly.

This species has not been common because most farmers plant wheat after “fly-free dates” -- dates after which egg-laying Hessian flies are not likely to be active. For Pennsylvania, fly-free dates have already passed (they range from 22 Sept – 1 Oct); recognize, however, that these fly-free dates are likely imperfect given the trend for warmer years due to climate change, so the proper dates are likely to be a few days later.

With great adoption of small grains as cover crop species, some growers have been planting wheat and barley in late summer or early fall. These early-planted fields are available for egg-laying female flies and then can foster populations of Hessian fly larvae that can then emerge as adults in spring and further infest fields. Planting after flies are active avoids this trouble.

Insecticides are generally ineffective for control of Hessian fly because larvae are protected by leaf sheaths and insecticides cannot reach them. Therefore, the best tactic for farmers is to adhere to the fly-free dates and plant Hessian fly-resistant varieties of wheat or barley. For more information on Hessian fly in Pennsylvania, see our fact sheet: https://extension.psu.edu/hessian-fly-on-wheat

Leon Ressler is a Penn State Extension educator based in Lancaster County, Pennsylvania.

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