Re‐evaluating fall cankerworm management thresholds for urban and suburban forests

Abstract

1 In recent decades, outbreaks of fall cankerworm (Alsophila pometaria, Lepidoptera: Geometridae) have increased in urban and suburban areas of the mid-Atlantic and southeastern U.S.A., including in Richmond, Virginia, as well as in Charlotte, North Carolina. 2 Managers in these regions commonly monitor fall cankerworm population trends using sticky band traps and use established thresholds relating the number of individuals captured to defoliation as a decision-making tool. For this pest, defoliation thresholds were established based on large forest tracts, although these may yield inaccurate predictions in urban and suburban landscapes. 3 Analyses of defoliation and fall cankerworm sticky band traps in Fairfax County, Virginia, U.S.A., indicate that trees with >200 female moths have >50% probability of being defoliated at moderate or greater intensity. This threshold is much larger than the threshold of 45 females previously established for large forest tracts, and a statistical model based on this established threshold proved an extremely poor fit to the data. In addition, we found little spatial correlation in fall cankerworm abundance among trap locations, in contrast to an established rule of thumb proposing that one trap per 40 ha can estimate fall cankerworm abundance for areas over 400 ha. 4 These findings highlight the importance of the ecological context in which management recommendations are made.