Patterns of Landscape‐Level Spread by Beech Leaf Disease in North America

Beech leaf disease (BLD) was first detected in North America in Lake County, Ohio in 2012. The disease is detrimental to beech ( Fagus spp.) trees and is caused by Litylenchus crenatae ssp. mccannii , a species of nematode that is likely native to Japan. The area positive for BLD has expanded into most of the northeastern United States and some parts of southeastern Canada, but the rate and patterns of spread have not been quantified. We analysed county‐ and census‐division‐level BLD occurrence records from the United States and Canada, respectively, to characterize the spatiotemporal dynamics of spread. The disease has spread an average of 33–43 km/year—depending on the analytical method used—while exhibiting marked anisotropy: spread rates averaged 105 km/year northeast but < 20 km/year southwest. These findings provide information that can support monitoring for BLD in North American forests.