Pathogen
The foliar nematode Litylenchus crenatae is responsible for beech leaf disease (Carta et al. 2020) and is believed to be non-native in North America. Presently, it's suspected that the nematode is native to Japan.
History, Distribution and Hosts
Beech leaf disease (BLD) was first discovered in 2012 from northeastern Ohio (Ewing et al. 2019). In New England, the disease was first detected in 2019 from southwestern Connecticut (Marra and Lamondia 2020) and several nearby counties in New York State. Currently, BLD is widespread across Connecticut, Rhode Island and Massachusetts. In addition, BLD continues to spread northward through Maine, New Hampshire and Vermont. This is especially concerning in areas where the northern hardwood (beech-birch-maple) forest type dominates. Many northern hardwood forests in western Massachusetts are primarily composed of American beech (Fagus grandifolia). According to the most recent USFS forest inventory and analysis, there are nearly 141 million American beech in Massachusetts, representing just under 10% of all forest trees >1" in diameter (USDA Forest Service 2020). Prior to BLD, no foliar nematode has ever been known to cause a disease of a forest tree that results in mortality (Carta et al. 2020). While uncertainty lingered for many years as to the cause of BLD, research has clearly linked the presence of the nematode to symptom development in natural and inoculated beech (Carta et al. 2020). American (F. grandifolia), European (F. sylvatica), Japanese (F. crenata) and Oriental beech (F. orientalis) are known hosts.
Symptoms & Life Cycle
Symptoms of BLD appear as: (i) dark-colored, interveinal banding on the foliage; (ii) cupping, curling and distortion of the foliage; (iii) thickening of the leaves and a general "leathery" texture; (iv) premature leaf shedding; and (v) death of the buds and subsequent branch dieback resulting in death of the tree. The interveinal banding is often dark green in color. The interveinal banding, cupping and distortion of the foliage may be caused by toxins, pectinases, phenolics or carotenoids produced by the nematode (Cara et al. 2020). It’s hypothesized that thicker, darker leaf tissue may protect the nematode against UV light and provide a larger number of cells for feeding.
Litylenchus crenatae invades beech buds from mid-summer into autumn (roughly late June into October), where they feed and overwinter (Reed et al. 2020). They likely have many vectors with birds and insects providing the best means of dispersal. It is within the buds that the damage takes place. During the late autumn and winter months, L. crenatae populations are high within infested beech buds (Reed et al. 2020). When disease severity is minor to moderate, symptomatic leaves emerge the following spring. When disease severity is high, buds are killed outright and no new leaves and shoots are produced. Nematode eggs produced within the buds are dispersed during budbreak and leaf expansion and may scatter throughout the canopy on splashing rainwater and wind. They can survive for long periods until sufficient moisture allows for hatching. Very large populations of nematode eggs exist within the aborted buds. When infested trees flush symptomatic foliage in the spring, a second flush of leaves may also occur. This second flush of foliage is disease free, but often stunted and unevenly produced through the canopy.
Numerous studies are investigating the vectors of BLD, disease etiology and management of the nematode. Much remains to be learned about this new and destructive disease. While initial reports from the Midwest suggested that mature trees could withstand the disease for many years (Ewing et al. 2019), trees in southern New England are dying rapidly after infection. Additional stresses such as drought, winter injury, site-related stresses (poor, compacted soils and physical injury), twig/branch cankering fungi (e.g. Asterosporium, Botryosphaeria, Nectria, Phomopsis, etc.), ambrosia beetle infestation (e.g. Xylosandrus), and other insects pests and pathogens all help to accelerate the decline of infested trees.
Management
Foliar Nematicide Spray: The locally systemic nematicide fluopyram can provide good to excellent control of BLD under certain conditions (Loyd et al. 2024). Reports and observations suggest that early season applications of fluopyram may be the most effective in controlling BLD. Specifically, applications made in May and early June as new foliage is developing. Because the nematodes emerge from infested foliage and migrate to the buds in highest numbers from late August into October (Reed et al. 2020), early season applications will target the nematodes inside the foliage before populations buildup over the summer and early autumn. However, beech treated with fluopyram later in the season (e.g. August and September) have also shown improvement the following year. Overall, the treatment window for BLD control using fluopyram appears to be variable, with successful application dates ranging from May to September.
Two commercial products formulated for use on woody plants are available. The first is Broadform, a combination product composed of fluopyram + trifloxystrobin. The Broadform label covers residential and commercial landscapes and "ornamental" hosts, including all species of beech (Fagus). Additionally, the supplemental Broadform 2ee covers recommendations to manage BLD, with a rate of 4-8 fl. oz./100 gal and an application interval of 7-21 days. Practitioners cannot apply more than 27.3 fl. oz. per acre per year. Current trials suggest that lower rates of application (i.e. 1-4 fl. oz. /100 gal) may provide the same level of control and that a 21 day interval is better suited for treatment given the staggered emergence of adult nematodes. The 2ee recommendation for BLD covers all northeast states and will continue to be updated as new data becomes available. The second product is Luna Experience, another combination product (fluopyram + tebuconazole) labeled for use on woody plants (including beech). However, Luna Experience is labeled only for agriculture use and not for woody ornamentals. Finally, Indemnify is a single fluopyram product but is labeled for use on turf only.
Fluopyram may not provide meaningful control when there are numerous untreated beech nearby from which nematodes can readily disperse onto treated trees. Because it must be sprayed throughout the canopy of infested trees, the risk of drift onto neighboring properties makes the use of fluopyram difficult to impossible in many residential settings. Additionally, fluopyram cannot be used near natural waterways (streams, rivers, ponds, etc.) or on properties with private drinking water (wells). This is due to the chemicals potential persistence in soil and water, the potential health risks associated with chemical exposure, and its toxicity to aquatic organisms (Rathod et al. 2022, Donley et al. 2024).
Presently, there is still uncertainty over whether fluopyram will kill L. crenatae eggs. Fluopyram has efficacy against certain plant parasitic nematodes, but for some, it does not kill the eggs (Schleker et al. 2022). Also, there is a moderate risk of resistance development when using fluopyram (Loyd et al. 2024). That means to avoid resistance development, fluopyram should be rotated with another nematicide. Presently, another nematicide labeled for use on trees with potential efficacy has not be identified. However, given that the majority of the L. crenatae population is spreading from forest settings where they would never encounter a nematicide suggests that at this time, the risk of resistance development is not a major concern when designing BLD treatment regimes.
Systemic Nematicide Injection: Arbotect 20-S (thiabendazole hypophosphite) was given a 24(c) special local needs label in Massachusetts that permits its use for control of BLD on beech (Fagus spp.). Additional states with this supplemental label include CT, MD, NH, NY, NJ, OH, PA, RI, VA, and VT. The results from early trials indicate that Arbotect injections can provide good control of BLD (Loyd et al. 2025). The label recommends 2.8 fl. oz. of Arbotect 20-S for every 5" of trunk diameter on smaller trees and up to 12 fl. oz. per 5" of trunk diameter for larger trees. Injections should be made on the side of the root flare once the foliage is mostly developed (early June onward in MA). Trees can be injected once every two years but this interval may be modified pending observations of treated trees (Loyd et al. 2025). Additional details of the SLN label can be found here: https://www.greenbook.net/syngenta-llc/arbotect-20-s
Phosphites: Soil or lower trunk application of phosphites (mono- and di-potassium salts of Phosphorous acid) may provide some level of BLD control, although results can vary considerably. A notable improvement in tree vigor may take several years of regular treatments. Phosphites have two modes of action: (1) through direct antifungal activity when applied in high concentrations; and (2) by stimulating the tree’s natural defense response (Thao and Yamakama 2009). The first mode of action likely has no value since BLD is caused by a nematode and not a fungus. However, the second mode of action, natural defense stimulation, may be how phosphites help to induce some level of disease resistance within infected beech. Phosphites have been used previously to control plant parasitic nematodes with mixed results. Reports and observations in Massachusetts indicate that phosphite application alone provides limited control of BLD on landscape trees. However, phosphites may still be useful in aiding in the control of other stresses, such as cankering fungi like Phytophthora or Nectria cinnabarina (coral spot canker).
Cultural: There are no cultural practices that can limit the spread and severity of BLD. Because the primary vectors of BLD are birds and insects, management aimed at limiting disease spread is not possible. There are no quarantine zones or best management practices associated with the disposal of infested beech material. Once BLD establishes in an area, it cannot be eradicated by the removal of one infested tree. BLD can move on nursery stock, therefore any beech stock should be carefully examined prior to purchase and planting. At this time, new plantings of American and European beech are not recommended.
References
Carta L.K., Handoo Z.A., Li S., et al. 2020. Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America. Forest Pathology, 50: e12580. https://doi.org/10.1111/efp.12580
Donley N., Cox C., Bennet K., et al. 2024. Forever pesticides: a growing source of PFAS contamination in the environment. Environmental Health Perspectives 132(7). https://doi.org/10.1289/EHP13954
Ewing C.J., Hausman C.E., Pogacnik J., Slot J., Bonello, P. 2019. Beech leaf disease: An emerging forest epidemic. Forest Pathology 49: e12488. https://doi.org/10.1111/efp.12488
Loyd A.L., Cowles R.S., Borden M.A., et al. 2024. Exploring novel management methods for beech leaf disease, an emerging threat to forests and landscapes. Journal of Environmental Horticulture 42(1): 1-13. https://doi.org/10.24266/0738-2898-42.1.1
Loyd A.L., Borden M.A., Littlejohn C.A., et al. 2025. Thiabendazole as a therapeutic root flare injection for beech leaf disease management. Arboriculture and Urban Forestry, 51(3): 215-225. https://doi.org/10.48044/jauf.2025.007
Marra, R.E. and LaMondia, J. 2020. First report of Beech Leaf Disease, caused by the foliar nematode, Litylenchus crenatae mccannii, on American Beech (Fagus grandifolia) in Connecticut. Plant Disease 104(9). https://doi.org/10.1094/PDIS-02-20-0442-PDN
Rathod P.H, Shah P.G., Parmar K.D., and Kalasariya R.L. 2022. The fate of fluopyram in the soil-water-plant ecosystem: a review. Reviews of Environmental Contamination and Toxicology, 260(1). https://doi.org/10.1007/s44169-021-00001-7
Reed, S.E., Greifenhagen, S., Yu, Q., et al. 2020. Foliar nematode, Litylenchus crenatae ssp. mccannii, population dynamics in leaves and buds of beech leaf disease-affected trees in Canada and the US. Forest Pathology, 50: e12599. https://doi.org/10.1111/efp.12599
Scheleker, A.S.S., Rist, M., Matera, C., et al. 2022. Mode of action of fluopyram in plant‑parasitic nematodes. Scientific Reports 12: 11954. https://doi.org/10.1038/s41598-022-15782-7
Thao, H.T.B. and Yamakawa, T. 2009. Phosphite (phosphorous acid): Fungicide, fertilizer or bio-stimulator? Soil Science and Plant Nutrition 55(2): 228–234. https://doi.org/10.1111/j.1747-0765.2009.00365.x
USDA Forest Service. 2020. Forests of Massachusetts, 2019. Resource Update FS-239. Madison, WI: U.S. Department of Agriculture Forest Service, Northern Research Station. 2 p. https://doi.org/10.2737/FS-RU-239