Fall Armyworm Outbreak In Wheat In Central Kentucky

FELIPE C. BATISTA AND DR. RAUL T. VILLANUEVA

PRINCETON, KENTUCKY

We visited a wheat field in Simpson County that was experiencing an outbreak of fall armyworm (FAW) Spodoptera frugiperda (Lepidoptera: Noctuidae) in mid-October (Figure 1). Most FAW larvae were in the 4th to 6th instar (late developmental stages), and part of the field had been completely destroyed (Figures 1, 2, and 3). The farmer applied bifenthrin on the same day we visited the field. We collected 90 caterpillars before and 50 caterpillars after the application to evaluate control efficacy in the laboratory. We observed 55% mortality 24 hours after spraying. A week later, all caterpillars collected before spraying had pupated, while most of those collected after spraying were either dead or had not pupated yet. We are still monitoring the pupae to determine whether they will develop into healthy, well-formed adults.

Management & Discussion

To achieve better results with insecticide applications, it is important to spray when caterpillars are still in the early stages of development when they are more susceptible to the insecticide’s action. In general, insecticides are less effective when applied during the later stages of pest development. Therefore, regular monitoring is a key step in the success of most pest management strategies. In addition to the higher efficacy of insecticides applied early, most of the damage has already occurred by the time caterpillars reach the 4th to 6th instar, even if the insecticide still provides some level of control (Figure 1). Monitoring enables early detection and timely intervention, increasing the likelihood of successful control and helping prevent yield losses caused by the pest.

The choice of insecticide is also a key factor for achieving effective control. In 2024, we visited some Davies County wheat fields after receiving reports of a significant outbreak of fall armyworms during the first half of October (2024 FAW outbreak). The efficacy of control was low, even though insecticides were applied during the early stages of pest development. Laboratory tests conducted at that time indicated that the local FAW population was resistant to most of the pyrethroids evaluated, except bifenthrin. In contrast, chlorantraniliprole and indoxacarb provided excellent control; however, these are higher-cost options. Rotating insecticides with different modes of action is essential to delay resistance development and preserve the efficacy of more affordable products over time (Insecticide resistance management).   ∆

FELIPE C. BATISTA AND DR. RAUL T. VILLANUEVA

UNIVERSITY OF KENTUCKY