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, and 5 counties in Ontario. A map is provided in Ewing et al and is reproduced below (map image accessed Feb 19 2019 at https://news.osu.edu/beech-trees-are-dying-and-nobodys-sure-why/) .
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. The most promising candidate is a previously undescribed nematode detected by David McCann of the Ohio Department of Agriculture. That nematode has since been described by Japanese researchers on Japanese beech F. crenata (Kanzaki et al.) and given the name Litylenchus crenatae. Thousands of live Litylenchus nematodes (at least 10,000) can swim out from a single leaf.
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. However, there is little premature leaf loss. 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
In Northeast Ohio, intensive monitoring of a subset of 13 plots in Cleveland Metroparks sites revealed a 4% mortality rate from 2015 to 2017. 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.
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