In Other News From the Neighborhood

Mayetiola destructor is thought to have evolved alongside the ancestors of wheat, barley, and rye in the Fertile Crescent region of the Middle East. It is believed to have been introduced into North America in the straw bedding of Hessian mercenaries during the American Revolution, making it likely the first invasive insect pest on the North American continent. Its common name became Hessian fly as a result of this introduction.

Hessian fly is now a permanent resident anywhere in North America where wheat, barley, or rye is grown. Populations of Hessian fly, and in turn economic losses, can effectively be held in check with the use of Hessian fly-resistant varieties, seeding winter cereals after the so-called fly-free date, and avoiding the green bridge with proper field hygiene by destroying volunteers of any host species early enough that the insect can not migrate to the newly seeded host species.

A few summers ago, Hessian fly infestations in spring wheat reached high enough levels in parts of NW Minnesota and NE North Dakota that growers and crop consultants took notice.  There are at least two plausible explanations that could help explain the observations made that year. The very dry fall of the preceding year may have resulted in less tillage, allowing volunteer wheat to be left standing.  The ample snow cover in the winter that followed, in combination with a genetic background that imparts winter hardiness to some of our commonly grown spring wheat varieties,  allowed those same volunteers to serve as the green bridge the following spring. Just as plausible is that cover crops that included winter rye were seeded before the fly-free date in that preceding fall and not terminated early enough that following spring to avoid the green bridge.

These observations prompted Drs. Janet Knodel and  Anitha Chirumamilla in 2023 to start a monitoring network for Hessian fly in North Dakota as part of their Integrated Pest Management efforts. Using special pheromone-laced sticky traps, the researchers have found Hessian fly more or less anywhere wheat is throughout in North Dakota.  Their findings confirm that the Hessian fly is endemic across much of North Dakota. The highest numbers were in the northeastern corner of the state, and that area also saw the greatest year-over-year increase in the number of flies.  The annual summaries of their efforts can be found in the 2024 summary report and in the September 19th issue of NDSU's Crop & Pest Report. 

Why care?  There is really no reason to think that what is being observed in NE North Dakota is not also happening in NW Minnesota. That is not a reason to panic.  It is simply a reminder that we can not ignore Mother Nature nor the knowledge we already have when introducing or changing cultural practices.  Assume that none of the winter wheat, spring wheat, barley, or winter rye varieties carry the genetic resistance genes for Hessian fly, therefore:

• Seed winter cereals, even when establishing them as cover crops, after the so-called fly-free date.
• Avoid the green bridge with proper field hygiene by destroying volunteers of any host species early enough that the insect can not migrate to the newly seeded host species before seeding in the fall or spring.