Department of Entomology
Entomological Notes

During the past decade, damage to wheat by Hessian fly has been minimal in Pennsylvania. This low incidence of damage can be contributed primarily to the use of wheat varieties that possess either complete resistance or moderate resistance to attack by Hessian fly. Also helpful in holding down fly damage has been the cultural practice of planting wheat after the "fly-free" date in late September or early October.

Life History

Hessian fly eggs. #512-11. Oregon State University in cooperation with EPA. 

Hessian fly pupa. #512-25. Oregon State University in cooperation with EPA. 

There are two generations per year, one in early fall and one in the spring. There may also be a third generation in July and August if moisture conditions are high enough for volunteer wheat to sprout and grow. When a summer or supplementary brood does develop, early-sown non-resistant wheat is often severely damaged.

The flies of the fall brood appear in late September and live for only about one week. They lay their eggs on the leaves of young wheat plants. If there are no wheat plants available, the flies will deposit eggs on barley and rye. This is why planting after the fly-free date is an effective control. If the flies emerge and die off before the new wheat plants are up the crop cannot be infested.

Maggots soon hatch from the eggs and feed on juices which they extract from near the base of the plants. They complete their growth before cold weather and pass the winter as puparium or "flaxseeds".

Damage

In the spring, adult flies emerge from the "flaxseeds" and lay eggs on the leaves. Upon hatching, the maggots work their way under the leaf sheath near the node. Their feeding at this site weakens the stem which results in the stalks breaking over before harvest. The maggots change into puparia about the time wheat heads out and they remain in the stubble as "flaxseeds" until fall.

Control

High mortality of Hessian fly from parasites is very common in the spring generations but cannot be relied upon for the high level of control we desire. Therefore we suggest the use of fly resistant varieties where feasible or plant wheat after the "fly-free date". The fly-free date for each county in Pennsylvania is listed below.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

Authored by: Stanley G. Gesell, Extension Entomologist

Dennis Calvin, Professor

Last updated April 19, 2000

DISCLAIMER

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Entomological Notes are intended to serve as a quick reference guide and should not be used as a substitute for product label information. Although every attempt is made to produce Entomological Notes that are complete, timely, and accurate, the pesticide user bears the responsibility of consulting the pesticide label and adhering to those directions.

Issued in furtherance of Cooperative Extension Works, Acts of Congress May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture and the Pennsylvania Legislature. D. Jackson, Director of Cooperative Extension, The Pennsylvania State University.

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