Beech Leaf Disease

Symptoms of Beech Leaf Disease

Beech leaf disease causes discoloration and a thickening between the veins of the leaves, creating a distinctive banding pattern. These bands are galls where the causal nematodes are found in high numbers starting in midsummer. This symptom is most noticeable when the leaves are held up to the sun and becomes more obvious later in the growing season.

Affected leaves may also appear cupped, deformed, or smaller than normal. In some cases, they become thickened and develop a leathery texture.

Buds, small twigs and branches can be killed. Over time, trees decline from bud death and the resulting reduction in leaf area for photosynthesis.  

Lower branches are often more severely affected than the upper part of the tree canopy. The higher humidity and lower light penetration in the lower canopy appear to create an environment that fosters nematode development. 

In trees that have been infected for several years, the canopy often becomes sparse, with noticeably thinner leaf cover. With advanced disease the trees can become weakened and die. Tree mortality can occur within 2-10 years, with shorter lifespans expected with smaller beech trees.  

Management of Beech Leaf Disease

Currently, there is no known cure for beech leaf disease (BLD), but some practices can help reduce its impact. Some treatments are now available that can reduce disease severity.

Management and Care Tips

Focusing on improving tree health, minimizing stress, and reducing conditions that may favor the nematodes responsible for the disease can help extend the life of affected trees.

• Mulch: Apply a 3-inch layer of mulch around the base of the tree (keeping it away from direct contact with the trunk). Mulch helps retain soil moisture, regulate temperature, and reduce stress on the tree.
• Water: During dry periods, water the root area of the tree to maintain soil moisture. Avoid using sprinklers or overhead watering systems that wet the foliage.
• Prune: Thin out the affected tree and nearby shading tree canopies to improve light penetration and air circulation. This can reduce moisture, which may help limit nematode activity and disease progression. Always prune when the foliage is dry, preferably at the end of the dormant season, to avoid spreading the nematode.
• Treatments:
  • Broadform (fluopyram and trifloxystrobin) sprays in rotation with phosphite fungicide have been shown in research trials to be very effective in reducing symptoms in the year after treatment. The active ingredient fluopyram is both a fungicide and a nematicide. Broadform is available for use by certified applicators with a 2ee label. Note that this material is highly toxic to fish and aquatic invertebrates, so it is not appropriate for all sites.
  • A phosphite product, PHOSPHO-jet, has a 2(ee) registration and applications of phosphites-based products have been shown to enhance the vitality and natural defenses of beech trees, potentially inhibiting nematode activity and reducing BLD symptoms.
  • Arbotect 20-S (thiabendazole) is an injectable product. The active ingredient thiabendazole is both a fungicide and nematicide. Research trials have shown it to be effective in reducing symptoms and nematode populations for at least 2 years. Arbotect 20S is available for use by certified applicators with a 24(c) label. It is applied every two years and is suitable for large trees.

Potential Solutions for the future: 

• Natural resistance: Some beech trees exhibit fewer symptoms compared to surrounding trees. These could be an important source of resistance for this disease. If you find a beech tree that seems to be resistant, please report it!  It could be useful in future efforts to breed resistant trees. An observation can be made through the free app TreeSnap.
• Microbial Communities: Research is underway to understand the role natural fungal and bacterial communities may play in potentially protecting trees from beech leaf disease nematodes.