Over the past weeks, more agents, consultants, and growers are noticing Hessian flies in fields that were not an apparent problem in the fall. The last time we had a major spring infestation was during 2012.
A similarity between that year and 2017 was an extended warm spell. This occurred during March of 2012, where average highs were above 70 degrees, and during February of 2017, where highs were in the mid to high 60’s. Although fall conditions might not have been great for Hessian fly, the extended warm during late winter was perfect for adults to emerge, lay eggs, and allow larvae to develop.
What can be done?
Is Hessian fly present? Scout wheat by pulling up clumps of plants and carefully dissecting tillers. Larvae or pupae will be located behind leaf sheaths at the plant base or at nodes on the stems of tillers that have elongated to form a spike. Scout known susceptible varieties first. A list of high yielding varieties with Hessian fly resistance ratings (if known) can be found here.
Hessian fly is present so are they causing damage? Keep in mind that any larvae that are feeding now cannot be managed. Any management action taken MUST focus on adults for the next generation. Our greatest concern should be fall feeding, which can cause tiller death.
Spring feeding can cause some yield loss, since larvae are taking nutrients from the plant, but a greater concern is lodging at harvest. This can occur from feeding at the base of the plant, or higher up, from feeding at the joints of the plant.
What can be done? A single trial, from my predecessor, Dr. John Van Duyn, was successful for a rescue treatment. Pyrethroid- class insecticides are effective when they are timed correctly to kill adults, reducing egg lay. This will be nearly impossible to do on a large scale.
I visited several fields today, same variety, similar planting date, and nearby to each other. The Hessian fly were in different developmental stages in every field that I visited. How could a spray be timed correctly on this one farm? Insecticide sprays must be specifically timed to kill adults as they emerge.