Response to the winter drench application and dosage of cyclaniliprole on Systena frontalis (Coleoptera: Chrysomelidae) in containerized panicled hydrangea

Systena frontalis (Fabricius) is a serious pest in containerized ornamental nurseries affecting > 50 plant species, including panicled hydrangea ( Hydrangea paniculata Siebold) in the eastern USA. The drench application of cyclaniliprole has proven effective in reducing the emergence of adult S. frontalis from infested containers; however, the effects of winter application and lower rates of cyclaniliprole are poorly understood. Thus, the objectives of this study were to determine the effects of 1) single and repeated drench application of cyclaniliprole in the winter and 2) reduced label rates of cyclaniliprole on the adult S. frontalis emergence and feeding damage in the containerized panicled hydrangea. In the winter of 2023 and 2024, cyclaniliprole was drenched in February, March, and April as a single and repeated application. Three repeated drench applications of cyclaniliprole reduced the emergence of adult S. frontalis by 94-100% and feeding damage compared to nontreated plants. The emerging adults and feeding damage during February, March, or April were similar to repeated applications, suggesting that a single drench of cyclaniliprole during the winter can effectively reduce adult emergence and is comparable to repeated applications. In addition, results showed that 0.25× and 0.5× rates of maximum label rate of cyclaniliprole applied as a drench did not consistently reduce adult S. frontalis emergence and feeding damage on panicled hydrangea as compared to the maximum label rate of cyclaniliprole. Thus, the maximum label rate of cyclaniliprole is needed to manage S. frontalis in ornamental nurseries. • Adult Systena frontalis can cause serious feeding damage on Hydrangea paniculata. • Three repeated drench applications of cyclaniliprole reduced the emergence of adult S. frontalis by 94-100% • Adult emergence was similar to single versus repeated applications in the winter • Reduced rates of cyclaniliprole drench applied did not consistently reduce adult emergence on panicled hydrangea as compared to the maximum label rate