The Hessian fly passes through 2 generations per year in which adult flies deposit eggs, maggots hatch on the leaves and feed on the stalks, and after feeding the maggots pupate into a form commonly recognized as flaxseeds.
The adults are active in the early spring and late summer. Damage by maggots occurs in the late spring and early fall. As a result, when damage is noted, the flaxseed pupae can often be located near the infested tiller in the spring or associated with broken stems observed in the early summer.
If a serious infestation of Hessian fly develops in the field, the problem is generally detected after the damage has been done and the fly is in the flaxseed stage. Thus, rescue treatments are not applied to prevent additional damage.
Prevention of Hessian fly damage depends on two cultural methods of pest management, namely: (1) planting varieties resistant to Hessian fly and (2) planting wheat in the fall after the late summer adult egg laying period has passed.
Detection of Hessian fly injury indicates an ommision of strictly following either or both of the recommended cultural practices in a geographical area.
Hessian fly control depends on breaking the life cycle in the fall by planting wheat after a 'fly free date'. If the fly population is allowed to gain a foothold in the fall, the spirng generation will be greater in number and cause significant damage.
Fly free dates in Ohio range from September 22nd near Lake Erie and Michigan to October 5th at the southern tip of Ohio. Wheat planted after the fly free date in the fall will escape the period of egg deposition by the fall brood.
| click to see Ohio map with fly free dates. |