Twospotted Spider Mite Preference and Performance on Day-Neutral Strawberry in New York and Role of Structural Characteristics in Plant Susceptibility

Abstract

Growing strawberries ( Fragaria× ananassaDuch.) under plastic low tunnels is increasing in popularity among growers in the northeastern U.S. despite reports of higher Tetranychus urticaeKoch (TSSM) pressure in this system. This study evaluated differences in susceptibility to TSSM among cultivars that are commonly planted in the Northeast. A second objective was to quantify differences in key structural characteristics (trichome density, leaflet area, average number of leaflets, and total above-ground biomass) that may contribute to variation in cultivar susceptibility to TSSM. We evaluated TSSM preference and performance using leaf disc and whole plant assays in the lab/greenhouse, and in the field at several commercial sites. Performance tests conducted on leaf discs yielded inconclusive results, but ‘Albion’ and especially ‘Seascape’ were identified as the least preferred cultivars by TSSM when assessed on whole plants. Of the structural characteristics measured, total above-ground biomass was the best predictor of TSSM number per leaflet, with larger plants having lower TSSM counts on leaflets. Total numbers of TSSM on whole plants were also higher on ‘Seascape’ which was the smallest cultivar tested in our study in terms of plant weight and leaflet area. However, there was no correlation between TSSM counts per leaflet and yield for any of the cultivars tested in the field. We discuss potential explanations for these results with implications on TSSM management under low tunnels.