Beech Leaf Disease in Maine
A disease that has been leading to decline and mortality of beech trees from Ohio to Southern New England has arrived in Maine’s forest. Beech leaf disease (BLD) was confirmed in a forest in Lincolnville, ME (Waldo County) in late May 2021 by Maine Forest Service and US Forest Service forest pathologists. This detection was reinforced by Dr. Robert Marra of the Connecticut Agricultural Experiment Station who confirmed presence of the causal agent nematode in submitted leaf samples by molecular methods. The diseased trees were brought to the attention of the Maine Forest Service’s Pathologist by the landowners, who pay close attention to changes in their environment during their frequent walks through their forest. It appears to be widespread in the immediate area of Lincolnville and can be found in several areas of the Midcoast region. The disease is found as far north as the Penobscot Experimental Forest and may be established elsewhere.
BLD was first reported in Ohio in 2012, and for many years it was known only in adjacent states and provinces. The disease was detected in 2019 in eastern New York, and in 2020 a concerted survey and outreach effort uncovered the disease in southern New England and other areas (see current BLD distribution map below).
- Which trees can get beech leaf disease?
- What does beech leaf disease look like?
- What else looks like beech leaf disease?
- How can I manage beech leaf disease symptoms in my trees?
- What do we know about beech leaf disease?
- What information is missing about beech leaf disease?
- Why is beech leaf disease a concern?
- Where can I report beech leaf disease?
- Where can I learn more about beech leaf disease?
All beech trees (Fagus spp.) are susceptible to BLD, including European and Asian species (this includes beech cultivars available in the nursery trade).
Symptoms of BLD include:
- Dark bands between the veins of leaves;
- Leaves are cupped, deformed, shriveled and may be smaller than usual;
- Leaves can be thick and have a leathery texture, unlike the papery texture of healthy leaves;
- Premature leaf drop;
- Aborted buds leading to sparse leaf cover;
- Thinning canopy.
Images: (top left) Dark interveinal bands indicating BLD infection as seen looking up into the canopy from the understory; (top right) The full range of upper leaf surface symptoms from undersized leathery leaves to banding at various severity levels to asymptomatic leaves, all on the same branch; (bottom left) Dark banding and leaf deformation associated with BLD infection; (bottom middle) BLD symptoms as seen on winter leaves persisting on beech trees; (bottom right) European copper beech impacted by BLD, showing green discoloration, leaf deformation and interveinal banding.
There are several other organisms that can change how beech leaves look. Below are the most commonly encountered and reported BLD look-alikes in Maine.
Woolly beech aphid
Woolly beech aphid (Phyllaphis fagi) causes leaf deformation and discoloration like BLD, however the leaves are often rolled or curled and do not show banding in between leaf veins like leaves impacted by BLD. Further, the discoloration from woolly beech leaf aphid is usually characterized by yellowing of the affected area and leaf margins. A clear sign of woolly beech aphid activity is the waxy filaments shed from the insects on the leaf underside. The damage caused by this pest is not serious and in most cases impacts the tree very little.
Erineum gall damage occurs interveinally (between veins) like BLD (left picture), however the banding is not dark, and white to red velvety patches (erineum) are typically seen on leaf undersides (right picture). The symptom is caused by the activity of microscopic eriophyid mites (family Eriophyidae) that alters leaf growth. The damage caused by this pest is not serious and impacts the tree very little.
Beech anthracnose (Discula umbrinella) causes various degrees of discoloration and deformation of leaves like BLD, but the fungus causes lesions (often round) leading to dead brown leaf tissue surrounded by yellow discoloration of leaf tissue (a halo) and no banding is associated with beech anthracnose. When symptoms are much more severe than those pictured, beech anthracnose can cause significant defoliation.
When in doubt, please report it!
Symptoms and signs of BLD can vary, and unusual leaf symptoms could indicate other tree health issues. Also, BLD symptoms have been seen on the beech leaves impacted by other organisms, including these look-alikes!
Maine Forest Service will continue to monitor developments as more is learned about this disease. However, at this time, there are no proven methods for management.
Pruning infected landscape trees may decrease foliar surface moisture and thus disease severity. Management recommendations for horticultural settings are developing as more is learned about the disease. Chemical applications are currently in trial phases.
To slow the spread of BLD, consider:
- Avoid moving beech tree material including branches, twigs, leaves and seedlings and nursery stock from affected areas.
- Closely inspect any beech nursery stock for symptoms of BLD before purchase and outplanting.
- Avoid moving soil or other organic matter from affected areas.
There is a lot that is still unclear about BLD. We do know:
- BLD can kill American beech, European beech, and many other beech cultivars of various origins;
- BLD symptoms are associated with the presence of a non-native foliar nematode (microscopic roundworm), Litylenchus crenatae mccannii;
- Disease symptoms tend to begin in smaller beech trees in the understory, however larger trees are also vulnerable to attack and decline;
- BLD may weaken beech trees over time, making them more vulnerable to secondary pests.
- How the disease spreads;
- Details of how the disease develops and impacts forest ecosystems and how that development is different in stands already ravaged by beech bark disease;
- Whether other organisms (bacteria or fungi for instance) are needed for disease development or if the nematode can cause disease without other agents;
- If there are other plants that could be impacted by the nematode or organisms associated with them;
- If there are effective ways to manage the disease (several methods are being tested for use in ornamental trees);
- If there are any beech trees with tolerance of or resistance to BLD.
American beech in Maine is already greatly impacted by a different invasive forest pest. The beech scale, introduced near the turn of the last century, makes beech vulnerable to attack from native fungi and the two together result in beech bark disease. This disease has made beech undesirable in the eyes of many who own and tend forests because thickets of diseased beech develop after some types of harvests. Even in this compromised state, beech plays an important role in Maine’s forests.
Beech is well known for producing beech nuts, the most nutritious of any of our hard mast species (‘hard mast’ is a general term describing nuts produced by forest trees, for example, oak acorns). Beech nuts are an important food source for many wildlife species. The early hairstreak, a rare butterfly; and the black bear, one of Maine’s iconic large mammals are two species that prefer beechnuts. Beech is also particularly important as a species that provides cavities for wildlife nesting or denning.
Even compromised by disease, beech is still used for wood products such as furniture and flooring among others.
More about American beech and wildlife (PDF | 3.61 MB) from the University of Maine and Maine Department of Inland Fisheries and Wildlife.
The Maine Forest Service is asking for the public’s help in identifying additional areas impacted by BLD. Photos of suspected symptomatic leaves can be submitted via our online form; reports can also be made to email@example.com or by calling (207) 287-2431. If possible, photos should include a clear shot of the underside of an affected leaf or leaves, however, please report concerns even if those photos cannot be provided.