Evaluation of the potential use of a systemic insecticide and girdled trees in area wide management of the emerald ash borer

Abstract

Emerald ash borer, Agrilus planipennis Fairmaire, has become the most destructive forest insect to invade North America. Unfortunately, tactics to manage A. planipennis are limited and difficult to evaluate, primarily because of the difficulty of detecting and delineating new infestations. Here we use data from a unique resource, the SL.ow A.sh M.ortality (SLAM) pilot project, to assess whether treating a small proportion of trees with a highly effective systemic insecticide or girdling ash (Fraxinus spp.) trees to serve as A. planipennis population sinks can result in discernable effects on A. planipennis population growth or ash mortality. Components of the SLAM pilot project included an extensive inventory of ash abundance across a heterogenous area encompassing >390km2, treatment of 587 ash trees with a highly effective systemic insecticide, and girdling 2658 ash trees from 2009 to 2012. Fixed radius plots were established to monitor the condition of >1000 untreated ash trees throughout the area from 2010 to 2012. While only a very small proportion of ash trees in the project area were either treated with insecticide or girdled, both tactics led to detectable reductions of A. planipennis densities and protected ash trees in areas surrounding the treatments. The number of trees treated with the systemic insecticide reduced larval abundance in subsequent years. In contrast, the area of phloem in the insecticide-treated trees had no discernable effect on A. planipennis population growth, indicating that the number of treated trees was more important than the size of treated trees. Significant interactions among girdled trees, larval density, and the local abundance of ash phloem indicate girdling trees has a positive, but complex potential as a management tactic.