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Scout Info
Kentucky IPM Pest Information Pages

HESSIAN FLY : Kentucky Wheat IPM

Hessian Fly


The adult Hessian fly is a small, fragile, black fly smaller than the common house mosquito (less than 1/8 inch long). The abdomen of the female is a dull red. Adult flies can be found clinging to food plants, or may be found miles away from any known food plant, having been carried on the wind.

Hessian fly adult
Photo by S. Bauer, ARS/USDA

Eggs are laid in the grooves of the leaves of host plants (wheat, barley, rye), and larvae are small white maggots which feed on plant sap. Larvae and puparia (called flaxseed) may be found between the leaf sheath and the stalk. This insect has two generations per year.


Larvae cause inconspicuous damage to the plant by feeding on sap that is exuded by the plant from rasped sites. Hessian fly can infest wheat in both the fall and spring. A fall infestation can result in stand loss due to stunted growth and broken plants. Heavy infestations can lead to death of plants during the winter. A spring infestation usually results in plants of reduced vigor and bad color. The presence of dark brown "flaxseed" (pupae) behind the sheaths of the lower leaves of the plant is a positive identification of Hessian fly infestations.

Flaxseed (Hessian fly pupae)

IPM Techniques and Scouting

  • Damage can be greatly reduced by following the recommended fly free planting date for your area and using resistant varieties.

  • When and where to scout: Check fields one time after first frost and from early spring until June. Check for the pupal (flaxseed stage) on weakened seedlings October through March. The number of sites you need to examine in a field is based on the size of the field.

  • How to scout: Look for thin, stunted chlorotic patches in the field and examine the base of these plants for the "flaxseed".

  • Record: Count and record the number of "flaxseed" found per ten stems at each sample site.

  • During May check for the small, white,maggot-like larvae in the leaf sheaths. In the fall and in June check for the "flaxseed" or pupal stage.

  • There is no rescue treatment, however, preventive measures may be used to avoid future infestations.

Hessian Fly Activity

Hessian fly activity

Please note: These dates are approximations only. This calendar was constructed using data from Kentucky, USA. These dates may not apply in your area. You may wish to contact your county extension agent or agricultural consultant for information tailored to your locality.

References and Additional Information

This site was created and is maintained by Pat Dillon, Department of Entomology, University of Kentucky, S-225 Agricultural Science Ctr North, Lexington, KY USA  40546-0091 (phone: 859/257-3571). Please send questions or suggestions to: pdillon@uky.edu