Planting Wheat This Fall? Planting Date Remains Your Best Defense Against Hessian Fly

Fall Planting Is Just Around The Corner

ADESHINA ADEWINTE AND DR. NICHOLAS TEETS

LEXINGTON, KENTUCKY

As Kentucky wheat growers prepare for another planting season, one of the most important management decisions is when to plant. While planting early can help field operations by distributing workloads and establishing a larger crop before winter, it increases the risk of Hessian fly infestations. Insecticide seed treatments are available to help protect young wheat, but they should be viewed as an additional management tool, not a replacement for planting at the recommended Hessian fly-free date.

Our 2025 field observations, detailed here, reinforce the importance of planting date for Hessian fly management.

Why does the Hessian fly-free date work?

Adult Hessian flies emerge during the fall and lay eggs on young wheat seedlings. Adults are short-lived, leading to a fairly predictable “fly-free date,” after which there are no adult flies around to infest wheat plants. Thus, delaying planting until the Hessian fly-free date reduces overlap between wheat seedlings and egg-laying flies, minimizing the risk of infestation and yield loss. For more than a century, this has been one of the most effective and economical cultural practices for managing Hessian fly in winter wheat. View the fly and the damage it causes.

What did we observe during the 2025 growing season?

During the 2025 field season, we evaluated how planting date and seed treatment influence Hessian fly infestations and wheat yield. Field experiments were conducted at the University of Kentucky Research and Education Center in Princeton.

Pembroke 2021 wheat was planted on four dates (September 23, October 6, October 20, and November 4) using three seed treatment programs: Untreated control, Fungicide only (tebuconazole), and Insecticide + fungicide (imidacloprid + tebuconazole).  Our results clearly indicate the benefits of planting date. The earliest planting date (September 23) experienced the greatest Hessian fly pressure, and correspondingly, the lowest yields, especially for plants that were not treated with insecticide. In contrast, wheat planted during October and early November had little to no Hessian fly infestation regardless of seed treatment, and yields tended to be higher.

These results illustrate two important points. First, significant Hessian fly infestations were only observed for the earliest planting date. When planting was delayed until October, infestations did not occur across all treatments. Second, seeds treated with insecticide and fungicide had substantially lower Hessian fly abundance in the earliest planting and produced the highest grain yield under those conditions. However, when wheat was planted during the recommended planting period, differences among seed treatments became much smaller because Hessian fly pressure was already low. Thus, while insecticide seed treatments can provide protection when wheat must be planted early, they should complement, and not replace, the use of Hessian fly-free planting dates and other IPM measures.

Recommendations for Kentucky wheat growers

Based on our 2025 field observations, we recommend the following as growers prepare for fall planting:

• Plant wheat at or after the recommended Hessian fly-free date for your region whenever possible.
• When operational constraints require early planting, use insecticide seed treatments, but recognize that they may not provide complete protection for some years.
• Periodically scout wheat fields after emergence for Hessian fly and other fall insect pests. (See Adewinle & Villanueva 2025)

Lessons Learned

The 2025 growing season once again highlighted that planting date remains the foundation of Hessian fly management in Kentucky wheat. While insecticide seed treatments reduced Hessian fly infestations for early planting dates, using the recommended Hessian fly-free date was the most effective way to eliminate pest pressure across our field trials. Selecting the appropriate planting date remains one of the simplest, most economical, and most effective Integrated Pest Management (IPM) practices available for protecting Kentucky wheat.

These are preliminary observations from an ongoing field study. Additional analyses and future growing seasons will further improve our understanding of planting date and Hessian fly management in Kentucky wheat.   ∆

ADESHINA ADEWINTE AND DR. NICHOLAS TEETS

UNIVERSITY OF KENTUCKY