Beech Leaf Disease (BLD) is a substantial threat to American beech (Fagus grandifolia) and all other species of beech (Fagus spp.) across the eastern United States.

American beech plays an important role in forest ecosystems.

As a late successional species, it adds structural diversity to a variety of forest types and its nut production makes it an excellent species for wildlife.

Beech leaf disease was first identified in Ohio in 2012 but has since been found across the eastern United States.

BLD is easily recognized by its distinctive dark green interveinal banding pattern on symptomatic leaves.

It is caused by a nematode that parasites tree leaves.

This damage is seen in most species of beech.

It can be more difficult to identify early in beech with dark leaves like “copper” beech (Fagus sylvatica “Purpurea”).

Symptoms: The dark bands in leaves become evident in early spring as leaves emerge fully symptomatic.

Under high levels of infection, leaf symptoms become more pronounced; leaves become leathery and crinkled.

These bands are because of cellular damage caused by nematodes in the leaf buds.

In forests heavily impacted by BLD, it may look like there is a drought that is impacting only beech.

Disease Progression: In spring, from May to June, there are few nematodes in diseased leaves.

The number of nematodes increases over the summer (July-August) and reaches a peak in late summer through early fall (September-November).

As the numbers build up within the leaves, nematodes will migrate from the infected leaves into the newly-forming buds.

Once nematodes reach the new bud, they will feed on the bud tissues, which causes cell enlargement of the bud scale cells and negatively affects the overall architecture of the developing young leaves by increasing their number of cell layers.

This damages the next generation of leaves and repeated damage will kill the infected beech.

The method of transmission between infected trees is unknown.

Treatment: Yard, Street Trees: BLD can be treated in yard trees by injections of thiabendazole (such as Arbotect 20-S).

According to the label, inject 2 to 8 fluid ounces of thiabendazole for every five inches of trunk diameter and dilute with 16 to 32 parts water for one part chemical.

For large trees with stems with a DBH (diameter at breast height) of eight inches or more, stems may be injected with up to 12 fluid ounces thiabendazole per five inches of trunk diameter.

Always read and understand the chemical label prior to applying.

Other products that show promising results against BLD are potassium phosphite, potassium polyphosphate and other potassium fertilizers.

The recommended application rate is two fluid ounces of phosphite products mixed with 14 ounces of water for every one inch of diameter and applied at the base of the infected tree.

Trees that have been damaged for multiple years may not be saved as the damage is too much for the trees to overcome. Long term research is still underway.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613