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Hessian fly is a pest of wheat and other small grain crops that dates back to the Revolutionary War, when it was introduced to North America from Europe on imported straw bedding. Today, Hessian fly remains a pest of concern in all major wheat growing areas.
In our region, Hessian fly has 2 generations per year. In the late summer, adult flies emerge and lay eggs on wheat, barley, rye, and other related hosts. The larvae hatch and crawl down the plant to feed at the crown. The larvae go through 3 instar stages before overwintering as a pupa at the crown of the plant. In the spring, adults emerge, eggs are laid, and the cycle begins again.
Feeding by newly hatched Hessian fly larvae can cause stunting, reduced winter hardiness, and death of fall-planted wheat. Plants that survive may lodge during grain fill in the spring, or fail to produce grain entirely. Although Hessian fly infestations can be very sporadic in our area, the risk of damage warrants a deliberate approach to management.
Management
Since Hessian fly infestations are difficult to predict, the most effective management tactics are preventative.
The primary strategy is to delay planting past the fly-free date – the period after which adult Hessian flies are no longer active and able to lay eggs. The long-standing fly-free dates for New Jersey range from September 27 (North) to October 6 (South). Keep in mind that these threshold dates were determined in the last century, and may be delayed when fall weather is mild. Recent work in Kansas has demonstrated that Hessian fly can remain active long past the established “fly-free date”, which calls the validity of these dates into question. Alternatively, those authors suggested the fly-free date be referred to as the “Best Pest Management Planting Date”.
The highest wheat yields have been observed when the crop is planted within 10 days to 2 weeks after the fly-free date. In fact, there are numerous potential drawbacks to early planting that go beyond Hessian fly; these include excessive fall growth and tillering, as well as increased risk of weed and disease issues. With the excessive rainfall we’ve experienced over the last week, and more coming tonight, delays in corn harvest will likely force small grain planting past the fly-free date for most NJ farmers.
Wheat varieties with genetic resistance and tolerance to Hessian fly are also available. However, many resistant wheat varieties have lost their efficacy over the years. Genetic resistance should always be used in combination with planting after the fly-free date, as resistant biotypes of Hessian fly are now prevalent due to the selection pressure from failure to integrate practices.
Lastly, due to the limited host range and poor flight ability of Hessian fly, crop rotation and destruction of any volunteer wheat are also recommended.