Evaluation of neo-nicotinoid insecticides applied as non-invasive trunk sprays

Neo-nicotinoid insecticides such as imidacloprid and dinotefuron are widely used in southeastern Michigan to protect ash (Fraxinus sp.) shade trees from emerald ash borer (EAB), Agrilus planipennis Fairmaire. These products are relatively safe for humans and have few non-target effects. Trees are generally treated annually by injecting the insecticide into the soil or into the trunk. The product is translocated to the canopy, where it affects adult beetles during the summer. Questions and concerns have arisen about the long-term effects of repeated wounding associated with trunk injection, the time required to apply or monitor trunk-injected products, and possible movement of soil-injected products into soil or ground water at some sites. We evaluated a non-invasive, effi cient, and simple method of applying imidacloprid or dinotefuron to the trunk of ash shade trees. This application method involves mixing the insecticide with Pentra-Bark®, a non-toxic, bark-penetrating surfactant (Agrichem, Medina, Ohio). The formulated solution is applied directly to the bark on the lower trunk of a tree with a common garden sprayer. Pentra-Bark®, originally used as an agricultural surfactant, has recently been shown to carry fungicide products through the bark and into the xylem tissue of fruit trees, where the product is then translocated to the canopy. In our study, we sprayed the bark on the trunks of the trees until they were wet from 20 cm to 1.6 m aboveground. The randomized complete block design was replicated at four sites to ensure that we evaluated a range of tree size and bark thickness. Mean diameter at breast height (DBH) of trees used in the study ranged from 5.0 inches at the site with the smallest trees to 15.5 inches at the site with the largest trees. There were six to 12 trees per treatment at each of the four sites. Each block consisted of trees treated with a non-invasive trunk spray of (1) imidacloprid + Pentra-Bark®, (2) dinotefuron + Pentra-Bark®, (3) a soil application of imidacloprid applied at the base of the tree with a Davey wand, (4) a trunk injection of imidacloprid applied with Mauget capsules (e.g., a positive control), or (5) left as an untreated control (Table 1). Dinotefuron treatment was not included at one site. Data were analyzed with analysis-of___________________________________________________ Emerald Ash Borer-Host Relations 53 EMERALD ASH BORER AND ASIAN LONGHORNED BEETLE RESEARCH AND DEVELOPMENT REVIEW MEETING—2006 variance or the nonparametric equivalents and multiple comparison tests (when ANOVA results were signifi cant) to assess effects of treatment and site (P 500 cm2, each) excavated on the trunk and four to six locations in the canopy. Overall EAB larva density was low at the site with the largest trees (<10 EAB/m2), and there were no signifi cant differences among treatments. At a second site where only imidacloprid treatments were applied (no dinotefuron treatment), the EAB population was moderate. Larva density was highly variable, however, and between-treatment differences were not signifi cant. At the third site, with a low to moderate EAB population, trees treated with dinotefuron + Pentra-Bark®, a soil application of imidacloprid, or the Mauget capsules had signifi cantly lower larva density than untreated controls. Trees treated with the imidacloprid + Pentra-Bark® spray did not differ signifi cantly from other treated trees or the untreated controls. On average, trees treated with the imidacoprid + Pentra-Bark® trunk spray, the soil application of dinotefuron + Pentra-Bark®, or the Mauget capsules had 50 percent, 71 percent, 75 percent and 81 percent fewer larvae per m2, respectively, than untreated controls. Density of EAB at the site with the smallest trees was very low; these trees were not debarked and will likely be used in 2007 studies.