A Beech leaf infected with beech leaf disease.
Vermont Department of Forest, Parks, and Recreation
A Beech leaf infected with beech leaf disease.

Region’s beech trees vulnerable to invasive roundworm

State foresters see evidence of beech leaf disease in multiple Windham County towns

Residents of Guilford have discovered the aftermath an invasive species of roundworm that devastates beech trees, the latest indication that the leaf gall nematode has reached southeastern Vermont and inflicting beech leaf disease (BLD) in its wake.

The presence of Litylenchus crenatae mccannii was first confirmed in Vernon last October by staff at the Vermont Department of Forests, Parks, and Recreation, and then in Dummerston, after locals submitted pictures of ravaged beech leaves to the agency's website.

The microscopic nematode has already spread to eight new towns in Vermont since the start of 2024 - among them are Rockingham, Jamaica, Grafton, and Townshend.

When a species that is not native to a region takes hold far from its natural enemies, it can grow and spread unchecked.

Litylenchus, native to Japan, has continued its scourge on both the American and European varieties of beech trees across the country. The nematode is "essentially a little tiny worm-looking animal," said Andrew Hirsch, protection forester for Windham and Windsor counties.

BLD, first discovered in Ohio in 2012, has since appeared in trees across several states in and around New England.

Hirsch said that calling the condition a "disease" is a bit of a misnomer, given that it's caused by a roundworm.

"A disease is more of a fungal infection, or something like that," he said.

The disease causes deformation of leaves and dieback (when parts on a plant's periphery are killed, such as branches and leaves).

Often, it kills the tree by depriving it of its ability to nourish the leaves with chlorophyll, the green pigment that lets plants absorb energy from light, by destroying the inner workings of the leaf to hinder photosynthesis.

In large numbers, the roundworms cause "bud abortion," as Hirsch puts it.

During the winter, nematodes feed on the leaf primordia in the buds, causing deformation of the leaves, if they even grow.

Essentially, Litylenchus destroys the inner leaf, stopping the tree's growth in its tracks before it even starts.

An important native tree at risk

BLD is "moving quickly through the state, so that's concerning," Hirsch said.

However, it's still "too early on to theorize if we're at risk of extinction," he said, adding that the state foresters are still asking questions such as, "How is it [Litylenchus] spreading this fast?"

According to state forestry officials, there is no known cure for BLD.

Very little is known about the roundworms and how temperature influences their spread and their damage. Researchers don't know how climate change exacerbates BLD, if at all.

Linda Hecker, chair of the Guilford Conservation Commission, theorizes that "climate change stresses local tree species, making them more susceptible to invasive predators" but this isn't proven as of yet.

Further adding to the stress of researchers and forest management teams is that another affliction - beech bark disease - is taking out trees at the same time as BLD.

Beech bark disease is caused when an insect, the beech bark scale (Cryptococcus fagisuga) feeds on the tree, leaving damage. That creates a path for a fungal pathogen to get into the tree and kill the bark, creating dead sections called cankers.

Savannah Ferreira, forest health specialist with the Vermont Department of Forests, Parks, and Recreation, notes that "beech is an important native tree that has associations with mushrooms, insects, and vertebrates that are benefited by its presence in Vermont, and trees that face multiple stress agents are not always able to keep up these associations."

Researchers are working to create an anti- Litylenchus pesticide, but the cost of treating the vast swaths of forest across the landscape of Vermont will likely not be viable.

Right now, the fungicides and nematicides being researched are not allowed under the state's pesticide certification program.

The telltale signs: what to do, what not to do

The most noticeable sign of beech leaf disease are dark or light stripes on leaves, between the veins. Sometimes the leaf will blister as well.

If you see stripes on a beech leaf or darkening from underneath when looking at a canopy, visit the Vermont Department of Forests, Parks, and Recreation's invasives page to report it.

The department warns people not to relocate untreated firewood that may contain Litylenchus organisms.

Experts recommend not cutting any beech trees to avoid losing ones that could be potentially resistant to the nematode. For example, occasionally smooth-barked beeches have been healthy in stands heavily infected with beech bark disease. Researchers are trying to discover something of the sort with BLD.

"In terms of management guidelines, we're still putting things like that together, getting more research," said Hirsch.

He recommended that the public focus on invasive plant management in forests instead of rushing to cut all their beech trees. He said that behind the scenes, "people are researching the vector - like how this disease is moving across the landscape."

Researchers are focusing on vectors, pesticides, and host resistance. To Hirsch's best knowledge, not many invasive nematodes have come to the U.S., so that makes the phenomenon hard to study. It's one of the first of its kind.

Although the nematode's presence is a concern, southern Vermont's forests have other trees that produce hard-shelled seeds and nuts.

"In Windham County, we have an oak component, and hickory," says Hirsch.

But in the hardwood forests of the Northeast Kingdom, where beech is one of the only species that produce such nuts, invasive plants could take control of the understory - the layer of vegetation between the canopy of trees and the forest floor - if the beeches were to be eliminated or thinned if Litylenchus were to reach the northern part of the state.

Though it would still bring little comfort if beeches were to be wiped out, Hirch says that at least here in Windham County, oak and hickory could cushion the blow on the ecosystem if beeches are destroyed by the roundworm.

"We have some tree species that already fill that role for wildlife forage," Hirsch says.

This News item by Siri Harrison was written for The Commons.

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