ACTION THRESHOLDS BASED ON PLANT DEFOLIATION FOR MANAGEMENT OF COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE) IN POTATO

Small plot held experiments were conducted to assess the yield response of 'Superior' potatoes to various levels of Colorado potato beetle, Leptinotarsa decemlineata (Say), defoliation during different potato plant growth stages. A pretransformed, weighted defoliation rating scheme was used to quantify leaf area loss from Colorado potato beetle feeding. Preliminary defoliation action or treatment thresholds were developed and evaluated in large plot experiments where the defoliation thresholds were compared with a conventional program in which insecticide was applied based on potato beetle numbers per plant. Use of the defoliation thresholds for timing of insecticide resulted in a reduction in the number of sprays with no significant reduction in tuber yield, compared with the conventional program. Action thresholds of 20% (plant emergence to early bloom), 30% (early bloom to late bloom), and 60% (late bloom to harvest) are proposed for use in eastern Virginia and are defined as the maximum level of potato beetle feeding damage (foliage loss) before yield loss occurs, given the usual, dry potato-growing conditions prevalent in eastern Virginia. Guidelines for use of the defoliation action thresholds in a Colorado potato beetle management program are presented.