Photo by K. Hamilton DATCP
DATCP’s Pest Survey Program completed its annual corn rootworm beetle survey this week.
Corn rootworm is the costliest pest to corn production in Wisconsin. This long-term survey helps inform rootworm management decisions by assessing current-year beetle populations. It also provides a forecast for potential larval root damage to next year’s corn crop.
Results of sampling throughout August indicate beetle pressure in grain corn fields has been moderate overall and similar to levels recorded in 2024 and 2023. The survey found a state average count of 0.5 beetle per plant, the same average documented during the previous two seasons.
Average beetle counts decreased or remained static in six of the state’s nine crop reporting districts and increased in three districts. The most significant change observed in 2025 was an eastward shift in beetle pressure into the southeastern counties, away from the usual corn rootworm hotspots in southwestern Wisconsin.
The highest averages were in the southeast (0.9 beetle per plant), north-central (0.8 beetle per plant), and south-central (0.7 beetle per plant) regions, though only the first two districts had average beetle counts exceeding the 0.75 beetle per plant economic threshold. Corn fields with high or above-threshold beetle populations comprised 19% of this year’s 229 sites, an increase from last year’s 15%.
Although the survey documented mostly low and moderate beetle populations in Wisconsin corn fields for the third year in a row, individual fields with high rootworm counts were found across the southern and north-central districts.
Effective corn rootworm management in these higher-pressure areas will continue to require a multiyear plan emphasizing rotation out of a continuous corn cropping system; selection of a dual or stacked mode of action Bt-rootworm (RW) and RNAi corn seed product; and, in some situations, the use of a soil-applied insecticide at planting, usually for corn products without Bt-RW protection. Crop rotation remains the most effective regulator of corn rootworm populations by breaking the lifecycle. This should be the foundation of integrated rootworm management.
