Evaluation of Insect Netting for Reducing Apple Clearwing Moth Infestation on Apple

Apple clearwing moth, Synanthedon myopaeformis (Lepidoptera: Sesiidae) is an invasive pest of apple trees of European origin, first detected in 2005 in British Columbia. Infestations have increased and become more severe since its initial detection; there has been an increased interest in ACM due to its potential link to Sudden Apple Decline in the region. ACM pupae have been observed primarily – although not always – infesting
apple tree graft unions, often opportunistically infesting burr knots, canker, or otherwise damaged or vulnerable tissue. Larvae infest the cambium layer for 1-2 years before emerging. During the 2020 and 2021 growing seasons, we evaluated insect netting (1/6″ square mesh polypropylene) applied over entire apple trees for management of ACM by assessing pupal casing counts near the graft union.. No effect was detected after one
season; however, this is likely due to ACM lifecycle and infestation from the year prior, when there was no netting applied. A reduction to 0% infestation with netting application was observed in a second season of use, while infestation increased in the un-netted treatments. Woolly aphid infestations were observed to be more severe in tree canopies under netting than in non-netted trees. It should be noted that this appeared to bean abnormal year for woolly aphid. Field evaluations will continue for at least one more season (2022); apple quality under netting vs under nonnetted, and spray pattern when applied through netting vs non-netted will be assessed in the final season.