Optimizing Foliar Spray Intervals and Rates of Isocycloseram and Cyantraniliprole Plus Thiamethoxam Application on Hydrangea paniculata to Combat Adult Systena frontalis (F) (Coleoptera: Chrysomelidae)

<i>Systena frontalis</i> (Fabricius) (Coleoptera: Chrysomelidae) is a challenging pest to manage in ornamental container nurseries, affecting over 50 plant species, particularly panicled hydrangea (<i>Hydrangea paniculata</i> Siebold). Because <i>S. frontalis</i> produces multiple generations and there is a risk of developing resistance to the insecticides currently used, growers urgently seek new tools, especially new active ingredients with different modes of action or new insecticide products. Isocycloseram (Plinazolin^® Technology) and cyantraniliprole + thiamethoxam (Mainspring^® Xtra) are new potential insecticides for managing adult <i>S. frontalis</i>. However, the effective rates and application frequencies and intervals of isocycloseram and cyantraniliprole + thiamethoxam are not well understood. Therefore, the objectives of this study were to determine how rates and application intervals of these insecticides affect feeding damage when applied as foliar sprays. In laboratory assays, applying isocycloseram 1.67 SC at 59.1, 118.3, 177.4, 236.6, and 295.7 mL in 378.5 L of water, as well as cyantraniliprole + thiamethoxam at 70.9, 141.7, 212.6, and 303.3 g, reduced feeding damage compared to nontreated controls. In field trials conducted in 2024 and 2025, leaves treated with isocycloseram at 118.3 and 147.9 mL in 378.5 L of water showed significantly less damage than nontreated controls. Cyantraniliprole + thiamethoxam at 226.8 and 283.5 g in 378.5 L of water also significantly reduced the number of damaged leaves compared to nontreated controls. Two to three repeated applications of isocycloseram 1.67 SC and cyantraniliprole + thiamethoxam, administered at 7 d intervals, significantly reduced leaf damage compared to two applications at 14 d intervals.