A Borer-Specific Assessment Scheme for Identifying Sentinel Trees to Delimit Invasive Borers in Urban Forests    (View PDF)

Gabriel P. Hughes, Clifford S. Sadof, and Matthew D. Ginzel

Abstract: Aggressive insects like the emerald ash borer [Agrilus planipennis (Fairmaire)] (EAB) increasingly threaten the health of the urban forest. Early detection of exotic wood-boring pests is critical for rapid response efforts, and allows for effective management while populations are relatively low. During street tree inventories, arborists record subjective rankings of tree condition and pest incidence; however, the extent of insect attack is rarely quantified. Moreover, it is unknown how the assessment of tree vigor provided by city foresters during these inventories relates to the likelihood of wood-borer infestation. In this study, researchers developed a borer-specific tree vigor assessment scheme to rapidly evaluate street trees, and to identify when EAB populations begin to grow exponentially based on the health of the forest. This scheme incorporates common indicators of EAB attack, including canopy thinning and epicormic sprouts, as well as attack by common native wood-boring insects. This scheme was used to track the health of ash trees from 2010 to 2013 in one urban forest with advanced symptoms of EAB decline and one without (Indianapolis and Lafayette, Indiana, U.S., respectively). Trees declined more rapidly in Indianapolis where emergence holes from native borers were positively correlated with EAB in infested areas. Over the course of the study, first detections of EAB occurred on progressively weaker trees at both sites, suggesting that early detection of incipient EAB populations can be improved by surveying apparently healthy trees.

Keywords: Agrilus planipennis; Early Detection-Rapid Response; Emerald Ash Borer; Surveys; Tree Inventory; Tree Vigor; Wood Borers.

https://doi.org/10.48044/jauf.2015.013