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 respons e of 'Superior' potatoes to various levels of Colorado potato beetle, Leptinotarsa decemlineata (Say), defoliation during different potato p lant growth stages. A pretransformed, weighted defoliation rating sche me was used to quantify leaf area loss from Colorado potato beetle fee ding. Preliminary defoliation action or treatment thresholds were deve loped and evaluated in large plot experiments where the defoliation th resholds were compared with a conventional program in which insecticid e was applied based on potato beetle numbers per plant. Use of the def oliation 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% (plan t emergence to early bloom), 30% (early bloom to late bloom), and 60% (late bloom to harvest) are proposed for use in eastern Virginia and a re defined as the maximum level of potato beetle feeding damage (folia ge loss) before yield loss occurs, given the usual, dry potato-growing conditions prevalent in eastern Virginia. Guidelines for use of the d efoliation action thresholds in a Colorado potato beetle management pr ogram are presented.