EPPO Alert List – Beech leaf disease
- An emerging disease of beech of unknown etiology -
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, 2020/082) 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, Ontario (Canada) and Connecticut.The disease has mainly been observed in forests but also in landscaped areas. A nematode species has been isolated from beech leaves and buds. At first, this nematode was identified as Litylenchus crenatae, a species described in Japan on Fagus crenata. Further studies conducted on American nematode populations concluded that they differed in morphology, host range, and ribosomal DNA marker from those in Japan. Therefore, it was proposed to consider the North American nematode associated with beech leaf disease as a new subspecies of L. crenatae, and to call it: Litylenchus crenatae mccannii. However, because the presence of L. crenatae mccannii has also been observed on asymptomatic bud and leaf tissue, the question as to whether nematode is the sole cause of the disease or is only a vector of unknown pathogens, remains unanswered and research is continuing in North America on the disease etiology. 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 subsequently supported by the Panel on Phytosanitary Measures.
North America: Canada (Ontario), USA (Connecticut, New York, Ohio, Pennsylvania).
On which plants
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.
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.
Pictures of symptoms observed can be viewed on the Internet: http://forestry.ohiodnr.gov/portals/forestry/pdfs/BLDAlert.pdf
If L. crenatae mccannii 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.
Plants for planting, cut branches of Fagus spp. from countries where the disease occurs?
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. crenatae mccannii plays a role in BLD or if the disease is associated with a complex of pathogens (e.g. fungi, bacteria, viruses or phytoplasmas). If L. crenatae mccannii is asociated with 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.
Burke DJ, Hoke AJ, Koch J (2020) The emergence of beech leaf disease in Ohio: probing the plant microbiome in the search of the cause. Forest Pathology, e12580. https://doi.org/10.1111/efp.12579
Carta LK, Handoo ZA, Li S, Kantor M, Bauchan G, McCann D, Gabriel CK, Yu Q, Reed S, Koch J, Martin D, Burke DJ (2020) Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America. Forest Pathology, e12580. https://doi.org/10.1111/efp.12580
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
Marra RE, 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 (early view). https://doi.org/10.1094/PDIS-02-20-0442-PDN
Pogacnik J, Macy T (2016-07) Forest Health Pest Alert. Beech Leaf Disease. http://forestry.ohiodnr.gov/portals/forestry/pdfs/BLDAlert.pdf
EPPO RS 2018/178, 2019/083, 2020/082, 2020/083