Comparison of standard (granular and drench) and novel (tablet, stick soak, and root dip) imidacloprid treatments for cottonwood leaf beetle (Coleoptera: Chrysomelidae) management on hybrid poplar

Standard soil application methods (granular and drench) were compared with novel methods (tablet, stick soak, and root dip) for efficacy and duration in hybrid poplar (Populus spp.) against adult and larval cottonwood leaf beetle, Chrysomela scripta F. (Coleoptera: Chrysomelidae). Beetle feeding can kill saplings and significantly damage trees by reducing tree height, diameter, and biomass. Tablets offer lower risk to applicators and beneficial insects, because insecticides do not need to be measured and sprayed. In field- and container-grown plants, standard granular and drench application methods had similar efficacy and duration compared with tablets. In field-grown plants, adult and larval survivorship was reduced for 12 mo with the two highest rates of tablet (0.25X and 0.5x) treatments, and in container-grown plants, with all rates of tablet (0.25x, 0.5X, and I X) treatments that were used. Two other novel application methods, stick soak and root dip, offer new methods for protecting vulnerable transplants in nursery propagation. In container-grown plants, adult survivorship was reduced for 8 mo and larval survivorship, for 12 mo for all rates of stick soak (0.5x, 1 X, and 2x) and all rates of root dip (I X, 2X, and 4X) treatments. Literature searches revealed little data on the efficacy and duration of soil-applied imidacloprid for trees, even though it is the primary insecticide used for defoliators and some borers in landscape and in nurseries for field and container production.