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RESEARCH LABORATORY TECHNICAL REPORT
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Beech Leaf Disease Andrew L. Loyd, PhD
Plant Pathologist
Beech leaf disease (BLD) is an emerging disease caused by a nematode, or microscopic worm. All cultivars of
American and European beech are susceptible. Beech are ecologically important trees in the eastern United States
and are common feature trees in landscapes. Beech leaf disease was first observed in Lake County, Ohio (Cleveland
area) in 2012. Since its initial detection, the disease has been observed in other counties in Ohio, Pennsylvania, New
York, Connecticut, and Ontario. BLD is caused by a foliar-feeding nematode, Litylenchus crenatae, which was
described initially on Japanese beech in Japan where it causes a mild disease. In the United States, however, healthy
beech trees have been observed dying in a period of six years from the onset of symptoms. As BLD progressively
worsens, the tree’s overall health weakens exposing it to secondary insect pests and diseases.
Symptoms
Symptoms of BLD typically progress from the bottom
of the canopy upward, but can be observed randomly
scattered throughout the canopy. Early symptoms
include distinct striping between the leaf veins (Figure
1), gall tissue in interveinal discoloration, and
darkening and/or chlorosis of the infested area.
Symptoms can be confused with leaf galls caused by
erineum mites (Figure 1). From the top of the leaves,
the interveinal discoloration will appear cupped or
puckered in appearance (Figure 2).
Figure 1: Leaf striping symptoms of BLD from the
underside of the leaf (left) and leaf galls caused by
erineum mites (right)
Figure 2: Interveinal leaf cupping/puckering
symptom of BLD
After successive years of being infested, leaves will
become deformed, chlorotic, and have a thickened,
almost leathery texture (Figure 3). By this stage the
photosynthetic capacity is reduced, and trees cannot
produce the amount of carbohydrates needed for
overwintering, resulting in a general lack of vigor. This
stresses the tree, and predisposes it to other secondary
invaders, such as insect borers and fungal cankers.
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Figure 3: Leaf deformation and thickening caused
by BLD
Causal Agent
The causal agent of BLD is the foliar-feeding nematode
Litylenchus crenatae (Figure 4). It is possible an
unknown microbe is being vectored by this nematode,
but no hard evidence has suggested this to date. This
nematode was described in 2018 on Japanese beech in
Japan and is thought to be native to Japan and other
parts of Asia. This nematode has an egg stage, several
juvenile stages, and an adult stage where both male
and female nematodes are present. Based on current
knowledge, this nematode only infests leaf tissue,
where it causes gall-like growths between the leaf
veins. The damage appears to occur while the leaf
tissue is in the bud. The nematode has not been
detected in woody tissues or roots. Adults of L.
crenatae penetrate wounded leaf buds, and overwinter
in buds as adults and eggs. Once the buds open in
spring, BLD symptoms are immediately evident on
infested leaves with numerous L. crenatae eggs being
present. As the season progresses, the eggs hatch in the
late spring and into the summer producing large
numbers of nematodes that will penetrate the buds as
they form in the summer.
Locally, the nematodes can move in shallow films of
water on trunks from rain, irrigation or melting snow.
In addition, there have been some reports of the
nematodes “hitching” a ride on non-flying arthropods
(e.g. spider mites), which can assist with local spread.
It is still unclear how the nematodes are moving long
distances, but birds have been suggested. Like many
diseases, human-mediated movement by installing
infested nursery stock is an additional way it can
spread long geographic distances.
Management
Avoid moving beech trees from areas where there are
known infestations. There is limited data on
preventive or therapeutic treatments for BLD. Several
products that have nematicidal properties are being
explored as potential options for management. Some
of these products contain active ingredients that are
derived from natural products produced by soil
microorganisms. These products are only labeled in
the United States.
Figure 4: Litylenchus crenatae adult male and egg
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