Beech leaf disease

Latin unknown, due to causal agent unknown
Faith Campbell with additions by Daniel Volk

In 2012, Ohio authorities detected a new disease attacking American beech (Fagus grandifolia) in Northeast Ohio. Initially they observed decline and mortality of beech saplings. Over the four years between 2012 and 2016, the apparent disease spread from an estimated 84 ha to 2,525 ha within Lake County, Ohio (Ewing et al. 2018).

By 2018, trees with symptoms had been detected in 24 counties across three states and one province: 10 counties in Ohio, 8 counties in Pennsylvania, 1 county in New York (Chautauqua), and 5 counties in Ontario. In May and June 2019, citizens reported finding symptomatic trees Fairfield, Connecticut (pers. comm. to F.T. Campbell). In October, Connecticut authorities confirmed the disease on beech trees in Greenwich, New Canaan, and Stamford (Connecticut Agricultural Experiment Station). Three additional findings were reported in Suffolk, Westchester and Rockland Counties, NY, in Fall 2019. Maps and other information are available at http://forestry.ohiodnr.gov/pests

The rate of decline within beech stands varies, suggesting that trees differ in susceptibility. This is a promising for breeding resistance (Ewing et al.).

The cause of beech dieback and mortality has still not been definitively determined. Most scientists agree that the cause is some kind of disease agent, not abiotic factors. Japanese researchers described a previously un-named nematode as Litlylenchus crenatae in May 2018 after studying it on Japanese beech F.crenata (Kanzaki et al.). The U.S. population (found by David McCann of the Ohio Department of Agriculture) was later described as a subspecies Litylenchus crenatae ssb mccannii by Lynn Carta. Thousands of live Litylenchus nematodes (at least 10,000) can swim out from a single leaf.

Symptoms

Early symptoms are dark striping on the leaves – best seen by looking upward into the backlit canopy. The striping is formed by a darkening and thickening of leaf tissue between leaf veins. Later, lighter, chlorotic striping may also occur. Eventually the affected foliage withers, dries, and yellows. Bud and leaf production is also affected.  Drastic leaf loss does occur for heavily symptomatic leaves during the growing season, as early as June, but asymptomatic and mildly symptomatic leaves show no or minimal leaf loss respectively. Both fully mature and very young “emerging” leaves show symptoms. For more complete descriptions and pictures of symptoms visit http://forestry.ohiodnr.gov/portals/forestry/pdfs/BLDAlert.pdf

Disease Progression

In Northeast Ohio, intensive monitoring of a subset of 13 plots in Cleveland Metroparks sites revealed a 7% mortality rate in 2018, primarily in saplings (Volk, pers comm). More than half of the plots now have dead trees that had previously been only symptomatic. While most of the dead trees are less than 4.9 cm dbh, some larger trees have died and others bear only a few leaves in summer. Sapling and pole-sized trees die within about three years after symptoms are observed. In areas where the disease is established, the proportion of American beech affected nears 100% (Pogachnik 2016).

Disease incidence does not appear to be influenced by slope, aspect, soil conditions, or weather. Also, while a wide variety of insects and pathogens is associated with symptomatic trees, these appear to be independent of beech leaf disease.

Leaves with light, medium, or heavy symptoms of infection – as well as asymptomatic leaves – can occur on the same branch of an individual tree.

The disease seems to spread through beech clone clusters along the interlocking roots.

Long range spread of the disease is probably assisted by anthropogenic transport, especially of nursery stock. Both European (F. sylvatica) and Asian (F. orientalis) beech have shown symptoms (Ewing et al. 2018). In the past, an Ontario retailer received – and rejected – a shipment of diseased beech from an Ohio nursery.

Online references

Ohio Department of Natural Resources, Division of Forestry, Forest Pests and Pathogens page http://forestry.ohiodnr.gov/pests

Report suspect trees or symptoms to ODNR, thomas.macy@dnr.state.oh.us, (614) 265-6705

Sources

Connecticut Agricultural Experiment Station. 2019. CAES Announces First Report of Beech Leaf Disease in Greenwich, New Canaan, and Stamford Connecticut. Press Release. October 17, 2019.

Ewing, C.J., C.E. Hausman, J. Pogacnik, J. Slot, P. Bonello. 2018.  Beech leaf disease: An emerging forest epidemic. Short Communication. Forest Pathology 2018;e12488

Kanzaki, N.,  Y. Ichihara, T. Aikawa, T. Ekino, and H. Masuya. 2019. Litylenchus crenatae n. sp. (Tylenchomorpha: Anguinidae), a leaf gall nematode parasitising Fagus crenata Blume. Nematology. Volume 21: Issue 1

John Pogacnik, Biologist, Lake Metroparks & Tom Macy, Forest Health Program Administrator, Ohio Department of Natural Resources Division of Forestry. Forest Health Pest Alert Beech Leaf Disease July 2016

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S., Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/