Beech Leaf Disease
The immediate impacts of a newly established pest.
Leaf banding on an infected beech tree - URI Plant Clinic
Summer 2023:
This season, we are seeing wide-spread Beech Leaf Disease (BLD) infection of European and American beeches (Fagus sp.). Many trees around the city dropped their spring leaves, which were damaged by the nematode worm causal agent of BLD. These trees look dismal, but many are putting out a second round of leaves in an effort to photosynthesize. Hopefully, these beeches will be able to photosynthesize enough this season to meet their energetic needs and store sugars for the winter ahead. Since present treatments for BLD are still experimental and not proven to eradicate the disease, we recommend taking extra care to water, mulch, and fertilize beeches to bolster their ability to deal with stressors.
NTC is a part of a BLD working group that includes researchers from around the world. While the consensus is that beeches across the range of the disease are visibly suffering this season, we are hopeful that resistant individuals will emerge. In Ohio, where the disease has been established for ten years, arboriculturists are attempting to graft beeches that have nematodes but show some degree of resistance to BLD. NTC’s Heritage Tree Center will be able to attempt similar grafting trials when suitable plant material emerges.
Winter 2022/23:
A brand new pathogen, only discovered in the Cleveland Ohio area in 2012, has made its arrival known in Newport. This disease, caused by a microscopic foliar nematode worm (Litylenchuys crenatae ssp. mccannii), has quickly established itself and poses a very serious threat to Newport’s finest collection of trees, our beloved beeches (Fagus sp.)
Beach Leaf Disease (BLD) was discovered in the western woodlands of Rhode Island in 2020, where it has wreaked havoc on wild populations of American beech (Fagus grandifolia). From there, it has spread throughout the entire state, including Newport in 2021, where many trees in our public parks and private properties are showing infection. Researchers worldwide are working to understand the multi-modal mechanisms by which the nematodes travel, including infected nursery stock, water droplets, and bird and insect droppings.
The disease can be easily identified as dark banding in between the leaf veins, best observed with sunlight illuminating the leaves. Dark bands are parts of the leaf where large numbers of nematodes have disrupted the cellular structure and are feeding. Advanced symptoms show foliage taking on a crinkled leathery texture, shriveling up and appearing deformed. Diseased leaves are unable to adequately photosynthesize. Since the nematode overwinters within the buds, trees will leaf out symptomatic in the spring. Nematodes have been found in buds, living and fallen leaves, and even on exterior surfaces of the bark. Defoliated trees may develop new growth in an attempt to boost photosynthetic production. Along with American beech, all species and varieties of European beech are susceptible, especially the straight species (Fagus sylvatica), and the purple (copper) leaf types which seem to decline at a faster rate. Based on observations in Ohio, mature trees seemed to handle infection better, whereas young trees succumb quickly. In 2023, mature trees across Newport and the region are showing more dire signs of stress.
So, how do we protect our trees? Research in Ohio has shown hopeful results when treating trees with phosphite-based fertilizers. Similar products, such as Agrifos and Prophyt, are used on beech to treat other ailments such as bleeding canker. The city of Newport has begun treatment of public beech trees using a similar product, Companion® Maxx Phosphite, applied as a soil drench. This phosphite based systemic fungicide will boost the plant’s systemic immune response on a cellular level to deal with infection or help protect from future infection. Arborists are also treating beech trees with Broadform®, a broad-spectrum fungicide. Scientists are studying the relationship between the nematode worm and fungus. The mechanism for killing the nematodes with fungicides is not yet fully understood.
It is also important to keep trees as stress-free as possible, as they will deal with pests better than stressed ones. Provide a thick layer of mulch under your tree to keep the root system cool, weeds suppressed, and moisture levels up. Provide supplemental irrigation in times of limited rainfall. Beech trees require a lot of moisture! It may also be beneficial to remove severely infected foliage from the tree and quickly rake and destroy fallen leaves in autumn, as the nematode is present in the foliage. The Newport Tree Conservancy, along with help from volunteers, is taking action to provide large mulch circles and water to beeches in the park space.
At the moment, there is no definitive treatment that will kill the pest and fully preserve infected trees. Research at universities and by tree healthcare professionals is ongoing. Trials using various fungicides have shown promising results in the early stages, killing the nematodes in high percentages. We are hopeful that future developments will lead to a treatment that will definitively control the nematode. But until then, it is important to give our trees a helping hand to conquer this pest and preserve our magnificent beech trees.
For more information, please visit:
https://web.uri.edu/ipm/2023/04/beech-leaf-disease-in-ri-2023-update/
https://dem.ri.gov/sites/g/files/xkgbur861/files/2023-06/disease-beech-leaf.pdf
