There are very few people who have the ability to scout Hessian fly eggs, due to their size. Several consultants who do have this skill have reported finding relatively high numbers of eggs on wheat during the last week. This is not just on early-planted wheat, but on wheat at the two to three leaf stage. It is likely a result of the warm weather. Contrary to popular belief, adult flies survive freezes. There is no such thing as a fly-free date in North Carolina. When a warm spell occurs anytime in the fall and winter, adults may become active and lay eggs.
There have been some cases where a foliar spray has been shown to have activity on adult flies. A threshold was set by my predecessor John Van Duyn at four eggs per leaf. I have not seen a case yet this year, where infestation levels have been this high. Wheat prices are higher and the threshold is likely lower than this. The question is, how low? Unfortunately, there is no research to answer this question.
I am willing to wager that 99% of our wheat in the state will not benefit from a foliar spray. You should only be worried about wheat that is susceptible to Hessian fly (click here for the list). I still stand by my past recommendation, except that wheat that was not planted early may now be at risk. Therefore, you should only spray if you’ve had historical problems with Hessian fly, did not use an insecticidal seed treatment, and have a susceptible variety. If you can spot eggs, you can add more assurance if you do or do not have Hessian fly. Furthermore, sprays are targeted at adult flies, with the hope of some residual to kill flies that may attack in the future. Sprays may have some efficacy on larvae as they hatch from the eggs, but this has never been demonstrated with research and is open to question. So a spray now will likely target adult flies in the future.