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09/01/2021 07:00 AM

A Tree Disease Gets Personal

The tree was probably planted around 1800, but beech leaf disease threatens its future.Photo courtesy of Kathy Connolly

A great European copper beech graces our front yard. Its crown is 80 feet wide and the trunk 10 feet around. Its dark purple leaves are remarkable in spring and summer, as is its copper color in late summer and fall. We think the tree was planted around 1800 by occupants of a nearby historical home. If so, it has lived through all the natural events of the 19th- and 20th centuries, including the infamous Hurricane of 1938.

Now, we worry that the 21st century be its last because our tree shows the symptoms of beech leaf disease (BLD).

According to Dr. Robert Marra, an associate scientist and forest pathologist at the Connecticut Agricultural Experiment Station, the disease is “easy to diagnose but hard to study.” BLD’s cause was undetermined from 2012 until 2020. Then, researchers identified the culprit, a previously unknown nematode.

Transmission, however, is still poorly understood.

Experimental Treatments

“Rain splash is probably part of the transmission,” says Marra. “The nematodes could also be hitchhiking on birds, mites, mammals, or insects.”

He also says that European beeches sold by nurseries may be a factor in the spread.

“It is a very new type of disease here in North America. We have no institutional experience in North America, nor Europe for that matter, with foliar nematodes on trees.”

As to an effective treatment, none is confirmed at this time though research continues. Marra says that some arborists have successfully experimented with a phosphonate soil applications, but conclusive research is not available. A treatment, when discovered, will be valuable for individual specimen trees.

The BLD nematode overwinters in leaf buds, which explains why leaves emerge fully symptomatic in spring. Affected leaves show bands between the veins, infested with the BLD nematode, appearing darkened when viewed from below, and puckered when viewed from above (see photos). The nematode does not live in the wood or bark.

Foundational Tree Species Threatened

Experience shows that some saplings succumb in only a few years. That should give me some hope for my aged copper beech, but another chapter in the saga unfolds at the nearby Preserve State Forest in Old Saybrook. There, BLD has wiped out countless beech saplings in the forest understory.

“American beech has been a foundational tree species of northern hardwood forests for a very long time,” says Marra. “They make up as much as one-third of the forests.”

He says it is too soon to know if older trees will adapt to the onslaught and stabilize.

With BLD hobbling the prospects for young trees, it is difficult to tell what will take their place.

“There is some speculation among foresters that the gaps created by beech loss might provide a release for oak or maple saplings,” says Marra.

On the other hand, there is also the possibility that non-native invasive plants will grab hold in the gaps left by fallen beech trees.

According to Maggie Redfern, assistant director of the Connecticut College Arboretum and founder of New London Trees, “Beech trees are loved by many people for their attributes. The European beech was commonly planted on estates throughout southern New England. Their smooth gray bark is easily recognizable; the trunk looks a bit like a giant elephant leg. Their massive trunks can grow to an impressive size, especially if given favorable conditions, and I would suspect that many people are amazed by the girth they achieve.”

She says the Arboretum has already lost a few beeches.

The Connecticut Notable Trees project lists 193 beeches whose size and beauty earned them a place on the list, many of them signature icons on town greens (see

What Can We Do?

Here are a few short-term steps we can take:

1. Reconsider plans for new beech plantings until a reliable treatment is available.

2. Stay up to date by reading press releases from the Connecticut Agricultural Experiment Station at Enter the word “beech” into the search bar to see a list of BLD updates.

3. Carry out fall leaf practices as usual. I was relieved to learn that we do not need to make a special effort to remove fallen leaves around infested trees. The predominant means of over-winter survival is via migration into nearby leaf buds.

This topic is discouraging, but as I look for a path forward, I am reminded of some larger lessons.

If a common tree such as beech, ash, oak, or maple succumbs widely to a new disease or insect, sunny gaps open where tree canopies and roots once prevailed. Landscape openings offer an engraved invitation to non-native invasive plants. That is especially true when those gaps occur near roadsides and forest edges where there is little or no maintenance. When trees come down, be prepared to replace them. Use a variety of native replacements, not just one species. Budget the time and money to give them healthy start. Continuously monitor for invasives.

The popular call to plant trees is meaningless if we don’t then care for the trees we have. Depending on the species, it can take 20 to 30 years before the investment in trees results in the amount of carbon capture, stormwater management, and air purification that are often described as the benefits of trees. We need to place higher value on mature trees. They are already productive.

Bottom line: There is little we can do today for beeches. But we can take stock of trees, both at home, in local parks, and on the street. Ask your town or neighborhood association to stay informed about BLD. Ask your town’s board of finance to budget for tree care, and hopefully someday, include a treatment for beech leaf disease.

How to Learn More

• Stay up to date on beech leaf disease: Visit and enter the word “beech” into the search bar to see a list of BLD updates.

• Learn about urban tree management: Connecticut Urban Forest Council,

• Find an arborist or get arborist training: Connecticut Tree Protective Association:

• Use online tools to assess the characteristics and contributions of trees in the landscape:

• Learn more about trees and identify trees from photographs:

• Learn about invasive plant management in Connecticut:

Kathy Connolly writes and speaks about landscape design, land care, and horticulture from Old Saybrook. For more information, email

The author’s copper beech leaves are rich purple in spring and early summer. The species color and size earned it a special place in Connecticut cities and towns over the past few centuries. Photo courtesy of Kathy Connolly
Viewed from the leaf underside, beech leaf disease shows dark bands between the veins. Photo courtesy of Robert E. Marra, CAES
Beech leaf disease is actually an infestation of nematodes in leaf buds. It causes beech leaves to appear puckered on the upper surface. Photo courtesy of Robert E. Marra, CAES