Organic management of apple flea weevil, a reemergent pest of commercial apples

• Published in: Organic agriculture 2016-09, Vol.6 (3), p.203-213
• Main Authors: Pote, John M., Nielsen, Anne L., Gut, Larry, Grieshop, Matthew J.
• Format: Article
• Language: English
• Subjects: Agriculture; Biomedical and Life Sciences; Environment; Life Sciences; Plant Sciences; Sustainable Development
• ISSN: 1879-4238; 1879-4246
• DOI: 10.1007/s13165-015-0129-z

Rhynchaenus pallicornis (Say) (Coleoptera: Curculionidae) is an economically significant pest of organically produced apples in Michigan. Although R. pallicornis has not been considered a pest of domesticated apples for over 50 years, it has recently reemerged with some organic producers experiencing >90 % yield loss as a result. We evaluated the effect of conventional and US Department of Agriculture: National Organic Program (NOP)-approved insecticides on adult R. pallicornis in the lab. Spinosad was the most effective organic compound tested (95.8 % mortality after 48 h). We then evaluated various application timings and rates of spinosad at commercial orchards. Applications of spinosad timed with the tight cluster stage of apple bud phenology caused the highest mortality of caged adults and significantly reduced the proportion of leaves with larval mines compared to an untreated control. Spinosad application significantly decreased the rate of parasitoid emergence from R. pallicornis larval leaf mines at one research site. The recommended application rate for spinosad in pome fruits is 219 ml/ha. We tested the efficacy of spinosad applied at 219 and 110 ml/ha for control of the summer generation of R. pallicornis. Half-rate applications (110 ml/ha) caused mortality similar to that of full-rate applications (219 ml/ha). Reduced application rates and informed application timings of spinosad may provide effective control of R. pallicornis while mitigating negative impacts on natural enemies.