Invasive Nematode Behind Beech Leaf Disease Rides Water, Wind and Birds

Beech leaf disease, caused by the invasive foliar nematode Litylenchus crenatae, has emerged as a serious threat to American beech (Fagus grandifolia) across North America. Since its first detection in 2012, the disease has reached 16 U.S. states and the Canadian province of Ontario, yet the mechanisms that move the microscopic worms across the landscape have remained poorly understood. A new study conducted at two forest sites in central Pennsylvania set out to test multiple potential dispersal pathways through integrated field surveys, environmental monitoring and experimental validation.

The researchers carried out weekly sampling to characterize nematode population dynamics in relation to temperature, precipitation, wind and humidity. Long-distance water-mediated dispersal was assessed by sampling creeks, while biotic dispersal was investigated by collecting material from the feet of migratory birds during high-moisture events and by running a controlled greenhouse transmission experiment. A pilot study also used unmanned aerial vehicle-assisted rainwater collection during precipitation events to examine wind-driven spread.

Nematodes were detected across all of the investigated pathways, supporting dispersal via water flow, rain splash and biotic vectors. Funnel-based sampling recovered Litylenchus crenatae up to 90 meters from infected trees, showing that the parasites can move well beyond the immediate canopy of a diseased tree.

Confirmed downstream transport of the nematodes suggests that waterways may act as corridors for long-distance dispersal across forested landscapes, potentially carrying the pathogen between otherwise unconnected stands of beech.

The team also recovered L. crenatae from the feet of migratory birds, and greenhouse experiments confirmed that nematodes associated with birds could infect healthy beech seedlings. This provides direct experimental evidence for avian-mediated transmission, implicating migrating birds as possible vectors in the disease’s rapid geographic expansion.

Desiccation assays added a key piece to the puzzle: live nematodes could survive up to 10 days without available moisture. This tolerance means the worms may remain viable while being transported on bird feet or other exposed surfaces, bridging the gap between leaving an infected tree and arriving at a new host.

Drone-assisted rainwater sampling detected the nematode within canopy-associated precipitation samples, offering additional evidence for short-distance aerial dispersal during wind and rain events. Together with the creek and bird findings, this indicates that rain splash and wind-driven droplets can move the parasite locally within and between tree crowns.

Taken together, the results show that beech leaf disease spread is driven by multiple interacting abiotic and biotic dispersal mechanisms operating across spatial scales, from rain splash within a single canopy to bird-mediated transport over much longer distances. The study was limited to two forest sites in central Pennsylvania, and the findings are observational and experimental evidence of pathway use rather than a full model of regional spread. Even so, identifying waterways, weather events and migratory birds as plausible routes opens new avenues for monitoring and managing one of North America’s most concerning emerging forest diseases.

Subject of Research: Dispersal mechanisms of the invasive beech leaf disease nematode Litylenchus crenatae in forest ecosystems

Article Title: When nematodes take flight: Multi-scale dispersal of the beech leaf disease nematode in forest ecosystems

Article References: Consoli, E., Berry, L., Lyndby, N., Wayman, M. R., DeGroote, L. W., Lindsay, A. M., Martin, D., Kantor, C., & Kantor, M. (2026). When nematodes take flight: Multi-scale dispersal of the beech leaf disease nematode in forest ecosystems. PLOS One, 21(10), e0361390. https://doi.org/10.1371/journal.pone.0361390

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0361390

Keywords: beech leaf disease, Litylenchus crenatae, nematode, forest pathology, dispersal, migratory birds, water-mediated dispersal, rain splash, drone sampling, Fagus grandifolia, invasive species, nematodes