This time of the year, you may be wondering if a spray would help eliminate Hessian fly problems in wheat. Our NC State recommendations are that you should only spray if you’ve had historical problems with Hessian fly, planted early, did not use an insecticidal seed treatment, and have a susceptible variety. You can find a list with varietal susceptibility at this link (click here). In the vast majority of these cases, using one of these management tactics will effectively manage Hessian fly. There are certain situations where multiple tactics are needed to prevent yield loss. These are only under the heaviest pressure situations and should be based on your past experience with this pest.
I have been working with the agents in northeastern NC, who planted a demonstration trial for Hessian fly on 19 October. This planting time was about two weeks before the recommended planting window for this part of the state. On Friday, 2 November, the wheat was at the two leaf stage. About 5% of the tillers had Hessian fly eggs. Hessian fly eggs are very tiny and generally impossible to sample without proper training. This is why our recommendation, listed above, does not include sampling for eggs. However, I would say that this level of egg lay and infestation is average for early-planted wheat in eastern NC. Many, if not most, fields have some low density of Hessian fly, especially if they are planted early. Based on these abundances, I would not recommend spraying this field. Assuming the wheat was a susceptible variety and had not received a seed treatment, a 5% tiller loss would be acceptable and could be made up as wheat puts on tillers in the spring. This is also assuming that there will not be a large “flush” of adults that move into the field and lay more eggs (probably a safe assumption, unless the weather turns warmer).
If you are located in eastern NC, have had historical problems in the past and meet the conditions listed in the first paragraph, you need to spray today (5 November). A spray today will correspond the best with the life cycle of the fly, the stage of the wheat, and will allow you to get in the field before this week’s impending wet weather. The point of the spray is to kill larvae as they hatch out of the eggs and move to the base of the plant. Once larvae reach the base of the plant, they remain protected from foliar insecticide sprays. Also, residual can probably affect adults as they begin to lay on wheat. Results are best when sprayed at the 2-3 leaf stage of wheat, or slightly before. Use the highest labeled rate of your choice of pyrethroid.