Recent visits to Edwards County wheat fields have revealed spotty but heavy infestations of Hessian fly. As an example, one field visited was planted on Sept. 25, just a few days shy of the “fly-free” date of October 1 in Edwards County. The variety planted on this field is susceptible to Hessian fly. In this case of fall infestation, Hessian fly adults likely emerged from the adjacent wheat stubble, then infested the nearby wheat seedlings in mid- to late-October. Even if the farmer would have planted after Oct. 1, some egg laying would still have occurred in this field because many of the adult Hessian flies emerged later than the fly-free date this fall.
Although the “Hessian fly-free date” is still a good general rule, that term is not completely correct anymore since Hessian fly adults have been caught flying up until December in some places in Kansas now.
Hessian fly infestations this fall are likely not limited to Edwards County since large populations of Hessian flies were detected in many areas in south central Kansas last spring. The adults were detected by sweeping wheat fields located near wheat stubble or in continuous wheat. Farmers should check now for the puparia or “flaxseed” stage (see below). Where infestations are found, farmers will need to evaluate the extent of the infestation and weigh the potential value of any further input costs on infested fields.
Hessian fly maggot feeding on seedlings in the fall can cause severe injury to plants. Infested wheat is stunted, and its leaves are dark green and broader than normal. Such injured plants will never grow past the four-leaf stage and will generally die during the winter.
If tillering has begun, then only infested tillers may die. To scout for the Hessian fly in the winter months, peel back the leaf sheaths to uncover the puparia. Flies in the flaxseed stage will usually emerge as adults in March or April and will fly to nearby areas to deposit their eggs onto wheat leaves.
There are no chemical management options for Hessian fly maggots or those in the flaxseed stage. Managing adult Hessian flies is not recommended either because emergence can be staggered over a period of several weeks -- yet adults live for only a few days. The best way farmers can prevent future infestations is to plant varieties of wheat that have greater resistance to Hessian flies and plant after the fly-free dates for their county.
For more detailed information on the Hessian fly in Kansas see the Hessian fly factsheet: https://www.bookstore.ksre.ksu.edu/pubs/MF2866.pdf,
Recommended management options are discussed here: https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=691
Sarah Zukoff, Southwest Area Extension Entomologist