Reports of Hessian Fly in wheat have been received from several locations in the RRV. Char Hollingsworth, plant pathologist at the UMN-NWROC (and an author in this newsletter) found a lot of puparia in the fungicide trial plots in Crookston last week.

Hessian fly is an introduced pest of small grains in the U.S. and is usually not a problem in Minnesota. It is a small, fragile fly, smaller than a mosquito (Figure 1); the flies are black with a slightly reddish abdomen and look somewhat like Orange Wheat Blossom Midge, though larger. The Hessian fly is believed to have two generations a year in our region, a spring and a fall generation. They overwinter and oversummer inside a flaxseed-like pupal case found at the base of the root crown and lower joints (Figure 2). The

presence of these flaxseed cases is a diagnostic sign that Hessian fly are present. Yield loss can occur from toxins released from the larvae while it feeds (which interfere with normal wheat growth) and from lodging associated with heavy populations.

While Minnesota generally does not have problem populations of Hessian fly, winter wheat planted early in the fall, may provide a fall egglaying site and a place for larvae to hatch, feed, and pupate on the “green bridge” that enhances overwintering survival and increases regional populations. Volunteer spring wheat that germinates in the fall can also serve this purpose. The plants do not have to survive the winter, only provide food necessary for larval development and a place to pupate.

There is little treatment other than varietal resistance as the larvae are feeding in locations unreachable by pesticides.In some areas of the country, they have looked at the chloronicotinyl seed treatments, such as Gaucho, as a control tactic, though it would be hard to justify a preventive program here with the problem still being rare. The BEST management strategy is still the avoidance of having suitable plants available for the flies to lay eggs on in the fall through either delayed planting or destruction of volunteers.

Ian MacRae
U of MN Extension Entomologist
and
Phillip Glogoza
Regional Educator - Crops