Submitted to: Forest Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Beech leaf disease (BLD) is a threat to the American beech tree throughout the eastern United States and Canada. The disease is strongly associated with a plant-parasitic round worm (nematode). The primary aim of this study was to follow the progression of BLD within natural forest stands throughout a single growing season. Results showed that BLD significantly reduces bud retention and subsequent foliage production among infected trees. Also, it was observed that the disease induced the output of second flush leaves as a stress response. Continued monitoring of BLD-impacted stands is necessary to assess long-term impacts on forest structure and function. This information is important for forest pathologists investigating potential methods for management of this disease.

Technical Abstract: Beech leaf disease (BLD) is an emerging threat to American beech (Fagus grandifolia Ehrh.) throughout North American forests and is strongly associated with the presence and abundance of the plant-parasitic nematode Litylenchus crenatae ssp. mccannii (Lcm). This study describes the impacts of BLD on bud retention and subsequent leaf production, associated symptoms, and the abundance of Lcm life stages throughout the course of a single growing season within two natural forest stands exposed to different levels of disease pressure. We found that trees with 2+ years of BLD infection exhibited reductions in bud retention that represented 52.3% fewer buds per branch (m-1) relative to a control stand that did not exhibit BLD symptoms in the previous year. Diseased trees also produced less foliage following spring bud break, corresponding to 67.8% few leaves per branch (m-1). Bud death among diseased trees resulted in a decoupling from the expected foliage production derived from winter bud inventories. Through the characterization of BLD symptoms expression among emerging leaves, including the presence of second flush leaves, we measured casting of severely symptomatic leaves coordinated with a marked increase in second flush leaves in the late summer. Nematodes counted within diseased trees ranged from 222-9,800 individuals per bud, while the proportion of live adults, eggs, and dead Lcm varied significantly between the spring and late-summer sampling periods. Together, our data provides important insights regarding the impact of a multi-year BLD infection on bud and foliage production, which has the potential to adversely affect tree carbon assimilation and long-term survival.