Systena frontalis (Coleoptera: Chrysomelidae), known as the red-headed flea beetle, is a key pest of ornamental shrubs in nurseries across the Eastern US. Considering the very low damage threshold in ornamental plant production, defoliation from this beetle can make plants unsaleable. Affected growers often spray weekly, or sometimes twice a week, in order to control this defoliator, relying heavily on pyrethroids and neonicotinoids. A significant challenge for the ornamental industry is to coordinate the timing between these foliar applications and the ongoing deployment of cultural practices, such as overhead irrigation, pruning and others. Overhead irrigation may physically ‘wash away’ the insecticide applied on plant canopies, especially when under a cyclic irrigation regime or during the summer months when plants are watered more often. The goal of this study was to document the potential interaction between irrigation (overhead vs. drip) and insecticide efficacy and residuality against S. frontalis on hydrangea plants under field conditions. Starting time for overhead irrigation cycles included 6, 12 and 24 h after the insecticide application. Adult densities and percent defoliation were recorded at 7 and 14 DAT from experimental plants. Preliminary data showed that higher defoliation was usually recorded from plants receiving overhead irrigation 6 h after the insecticide spray. Additional repetitions will be performed to corroborate these initial findings. Results from these experiments will increase our understanding of how overhead irrigation may influence the performance of foliar insecticide sprays. This data will also help growers manage the timing between foliar sprays and the irrigation regime.
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