2nd Place: Quantifying asiatic garden beetle damage in commercial mint

The Asiatic garden beetle (AGB) Maladera castanea Arrow has become a serious pest of commercial mint fields in northern Indiana. The larval (grub) stage feeds on mint roots, causing stunting and even plant death when feeding damage is severe. However, the relationship between grub density and yield loss is unclear, leaving growers without the fundamental knowledge necessary to implement a sound IPM approach. We quantified this relationship with a series of field visits designed to sample and assess mint plant performance in response to the varying densities of AGB larvae already present. We estimated larval density and plant biomass within 0.25m² quadrats taken from 30 randomly selected plots over a 0.4 ha area in 3 commercial fields during the spring/fall of 2021 and 2022. Regressions were performed to assess the relationship between larval density and plant biomass for each sampling event (field x season) (n = 12) and after pooling data based on season (spring vs fall) (n = 2). Above-ground biomass decreased with increasing larval density during the fall when mean larval densities were ³15 grubs/0.25m² (species composition = 95% AGB). Based on our pooled data, we were also able to predict the probability of experiencing reduced mint yields as a function of AGB larval density using a simple logistic model. Coupled with previous knowledge of the AGB’s life history and a practical understanding of grower operations, our results provide the basis for making science-based management recommendations to mint growers concerned about AGB in commercial mint.