Alternative application techniques of pesticides to control above and below ground herbivory of Polydrusus impressifrons in hybrid poplar cuttings

Hybrid poplars are an irrigated perennial monoculture propagated by planting branch cuttings.  The new roots and shoots of these cuttings are an attractive food source for herbivores.  Polydrusus impressifrons is a European species that was first reported in northeastern Oregon in 2004 and caused significant crop loss on GreenWood Resources Boardman Tree Farm in 2010.  Over two-thirds of the hybrid poplars in the Pacific Northwest are grown under a certification program that restricts the use of most conventional insecticides that would control these pests.  As a result, alternative insecticides must be evaluated within this cropping system to determine their ability to control this weevil pest.  We examined the efficacy of multiple pesticides and application techniques (48hr soak, spray and chemigation) to control the larval and adult stages of P. impressifrons.   No-choice feeding trials in the field and laboratory were used to determine the potential for adult control through pest mortality and leaf area loss.  Larval control was evaluated by measuring tree vigor.  Cuttings soaked in either imidacloprid or thiamethoxam suffered the least amount of damage from adult P. impressifrons in both laboratory and field trials.  Topical applications of indoxacarb and chlorantraniliprole controlled adult weevils in laboratory trials but were not effective in preventing damage in field trials.  Our results indicate that thiamethoxam applied via chemigation may provide some control of larval P. impressifrons.   Overall, the alternative application technique of soaking cuttings in a neonicotinoid solution prior to planting shows the most promise in controlling P. impressifrons in this system.