Abstract A complex of lepidopteran pests infests mint fields in the Pacific Northwest. Identified pest species include: cabbage looper (Trichoplusia ni), alfalfa looper (Autographa californica), and variegated cutworm (Peridroma saucia). However, our research has determined that early- spring feeding by spotted cutworm (Amathes c-nigrum) has the greatest negative impact on mint oil yields. A. c-nigrum overwinter as 2nd through 5th instar larvae in plant debris and soil directly beneath dormant mint. Feeding commences as the mint plants break dormancy, typically in mid- March. Our research indicates that treatment is necessary when A. c- nigrum populations exceed a density greater than 1.5 larvae per ½ m 2. Since 1999 we have monitored mating flights of A. c-nigrum and have determined that there are two complete generations per year. It is only the overwintering generation that causes economic damage to mint crops in the Pacific Northwest east of the Cascade range. Insecticides have been field-evaluated over the past several years to determine their potential for controlling early-spring A. c-nigrum on peppermint. Traditional insecticides including acephate, chlorpyriphos, and lambda-cyhalothrin have proven effective at controlling A. c-nigrum, whereas newer insect growth regulators and stomach poisons are not effective. We speculate that the IGRs and stomach poisons are not effective under PNW cold spring conditions. Objectives Test candidate insecticides for efficacy on pest caterpillars Develop recommendations for application of acephate through center-pivot irrigation system Study spotted cutworm biology and behavior Introduction A complex of lepidopteran pests infest mint fields in the Pacific Northwest. Identified pest species include: cabbage looper Trichoplusia ni, alfalfa looper Autographica californica, and variegated cutworm Peridroma saucia. However our research has determined that early-spring feeding by spotted cutworm, Amathes c-nigrum, has the greatest negative impact on mint oil yields. A. c-nigrum overwinter as 2 nd though 5 th instar larvae in plant debris and soil directly beneath dormant mint. Feeding commences as the mint plants break dormancy, typically in mid-March. Our research indicates that treatment is necessary when A. c-nigrum populations exceed a density greater than 1.5 larva per ½ m 2. Since 1999 we have monitored mating flights of A. c-nigrum and have determined that there are 2 complete generations per year. It is only the overwintering generation that causes economic damage to mint crops in the Pacific Northwest east of the Cascade range. Acknowledgments Washington Mint Commission Mint Industry Research Council Washington State Commission on Pesticide Registration Applications were made at 40 gallons per acre Summary Good control of cutworms was obtained using chlorpyrifos, acephate, -cyhalothrin, spinosad, and thiamethoxam. Comparable cutworm control was obtained with chemigated acephate and indoxacarb (2002). From pheromone trap data, two generations of spotted cutworms were observed annually; the 2 nd overwintering generation causes damage the following spring. Amathes c-nigrum trap catches from 3 locations in south-central Washington State. Two complete generations were observed annually. Moths per trap A ½ m transect was used for population estimation Cutworm Control on Pacific Northwest Mint Holly Ferguson, Ronald Wight, Timothy Waters, & Douglas Walsh Prosser, Washington