Beech leaf disease and its potential causal agent (Litylenchus crenatae): addition to the EPPO Alert List
Why: A new disease of beech trees (Fagus spp.) called 'Beech leaf disease' (BLD) has increasingly been observed in forest areas in Eastern USA and Canada (EPPO RS 2018/178) and is raising serious concerns among foresters and local communities in affected areas. The disease was first reported on Fagus grandifolia in Ohio (Lake county) in 2012, and it rapidly spread to other counties in Ohio, as well as to Pennsylvania, New York, and Ontario (Canada). The disease has mainly been observed in forests but also in landscaped areas. The cause of this emerging disease remains to be elucidated, but a nematode species, Litylenchus crenatae n. sp., newly described from Japan on Fagus crenata, is now suspected to be at least one of the causal agents of BLD. Considering the threat that this new disease of uncertain etiology represents to beech trees, the NPPO of the United Kingdom has added it to the UK Plant Health Risk Register and also suggested to add it to the EPPO Alert List. This proposal was supported by the Panel on Phytosanitary Measures.
Where: As it is still unclear whether L. crenatae is the causal agent of BLD, distribution data is presented separately for the disease in North America and the nematode in Japan.
North America (BLD): Canada (Ontario), USA (New York, Ohio, Pennsylvania).
Asia (L. crenatae): Japan (Hokkaido, Honshu).
On which plants: In North America, BLD mainly affects F. grandifolia (American beech). However, it was also observed in 2016 on F. sylvatica (European beech) and F. orientalis (Oriental beech) in a tree collection (Holden Forests and Gardens in Geauga county, Ohio), as well as in 2017 on F. sylvatica in commercial nursery stock (Lake county, Ohio). F. engleriana (Chinese beech) is considered to be a potential host. In Japan, Litylenchus crenatae has been described from leaves of F. crenata (Japanese beech).
Damage: In North America, early symptoms of BLD include dark-green striped bands between lateral veins of leaves and reduced leaf size. Banded areas usually become leathery-like, and leaf curling is also observed. As symptoms progress, aborted buds, reduced leaf production, and premature leaf drop lead to an overall reduction in canopy cover, ultimately resulting in death of sapling-sized trees within 2-5 years and of large trees within 6 years. In areas where the disease is established, the proportion of symptomatic trees can reach more than 90%. However, it is noted that some variability in susceptibility has been observed among beech trees.
In Japan, L. crenatae has been described on F. crenata displaying leaf galls and interveinal striped areas.
Pictures of symptoms observed can be viewed on the Internet:
In the USA: http://forestry.ohiodnr.gov/portals/forestry/pdfs/BLDAlert.pdf
In Japan: https://brill.com/view/journals/nemy/21/1/15685411_021_01_s002_i0013.jpg
Dissemination: Until now, L. crenatae has only been confirmed to be present within leaf tissues (mesophyll) of infected F. crenata in Japan. If this nematode is the main cause of BLD, plants for planting and cut foliage could be potential pathways for long distance transport. However, how the nematode spreads among forest trees is currently unknown. In particular, it is not known whether the nematode can survive in other plant parts or in the soil during winter after beech leaves have fallen.
Pathways: Plants for planting, cut branches of Fagus spp. from countries where the disease occurs?
Possible risks: Fagus spp. are widely planted in the EPPO region for forestry and amenity purposes. In particular, F. sylvatica is an important deciduous forest tree in Western and Central Europe (e.g. used for wood production). Many aspects remain to be clarified, in particular, it is still unclear whether L. crenatea is the sole causal agent of BLD or if the disease is associated with a complex of pathogens (e.g. fungi, bacteria, viruses or phytoplasmas). If L. crenatea is the main causal agent of BLD, its biology and epidemiology also need to be further studied to better assess its potential risk. However, considering, the rapidity of spread and the severity of damage (i.e. tree decline and mortality) observed on Fagus species in North America, it was felt that the attention of NPPOs should be drawn to this emerging disease and the potential risks it may present to the forestry and ornamental sectors of the EPPO region.
EPPO RS 2018/178, 2019/083
Panel review date – Entry date 2019-04
Ewing CJ, Hausman CE, Pogacnik J, Slot J, Bonello P (2018) Beech leaf disease: an emerging forest epidemic. Forest Pathology e12488. DOI: 10.1111/efp.12488
- Center for Invasive Species Prevention (2018-05-17) Invasive Species. Update on Beech Leaf Disease, a threat lacking adequate funding and official action. http://www.nivemnic.us/update-on-beech-leaf-disease-a-threat-lacking-adequate-funding-and-official-action/
- Central Pennsylvania Forestry (2018-03-08) Look for Beech Leaf Disease. http://centralpaforest.blogspot.com/2018/03/look-for-beech-leaf-disease.html
- Don’t move firewood. Beech leaf disease. https://www.dontmovefirewood.org/pest_pathogen/beech-leaf-disease/
- Lake Metroparks. Beech leaf disease. A new problem to our forests by J. Pogacnik (2018-08-14). https://www.lakemetroparks.com/along-the-trail/august-2018/beech-leaf-disease
- Ohio Department of Natural Resources Forestry Division (2018-08-20) ODNR urges Ohioans to report Beech Leaf Disease. http://forestry.ohiodnr.gov/news/post/odnr-urges-ohioans-to-report-beech-leaf-disease
- USDA. We need your help. Look for signs of Beech Leaf Disease. http://files.constantcontact.com/3eb6bf61101/a51df273-005c-4330-88eb-e4ea5294ea0d.pdf
Kanzaki N, Ichihara Y, Aikawa T, Ekino T, Masuya H (2019) Litylenchus crenatae n. sp. (Tylenchomorpha: Anguinidae), a leaf gall nematode parasitizing Fagus crenata Blume. Nematology 21(1), 5-22. DOI: https://doi.org/10.1163/15685411-00003190
Pogacnik J, Macy T (2016-07) Forest Health Pest Alert. Beech Leaf Disease. http://forestry.ohiodnr.gov/portals/forestry/pdfs/BLDAlert.pdf