Mystery surrounds disease threatening CT trees
There’s a lot about beech leaf disease that nobody knows.
Botanists don’t know how the pest — a nematode — that’s causing the disease got to North America. They don’t know how the disease is jumping from place to place or how, in nine years, it has spread from a small county in Ohio across Pennsylvania and New York into New England as far north as Maine.
But they do know this: It is spreading, and fast, threatening one of the most beautiful and important trees in the forests of the Northeast.
“On 2021, it exploded in Connecticut and Long Island.” said Robert Marra, an associate scientist at The Connecticut Agricultural Experiment Station’s department of plant pathology and ecology.
Marra — who has taken the lead on studying the disease in the state — spoke last week at the experiment station’s annual Plant Science Day at its Lockwood Farm research center in Hamden.
He described the manifestation of beech leaf disease in the scientific terminology adopted by his staff as “crazy Martian stripes’’ — dark brown, diagonal stripes on the underside of beech trees’ green, translucent leaves.
“The best way to see it is to stand under a tree and look up with the light behind you,” he said. “It’s absolutely diagnostic.”
Researchers first found beech leaf disease in a few spots in Fairfield and New
Haven counties in 2019. By 2021, Marra said, it has spread across the lower half of the state.
“It seems to be hugging the shoreline,” he said.
But it’s also been found in selected sites in Litchfield County and other places in the state’s northern tier.
“It’s all over New England,” said Chris Martin, director of forestry with the state Department of Energy and Environmental Protection. “We’ve seen beech die-back in some of the state forests in central Connecticut.”
“It’s widespread,” said Pat Flynn of Bartlett Tree Service in Danbury and president of the Connecticut Tree Protective Association.
Bruce Bennet, Kent’s tree warden, said the leaf disease hasn’t shown up in his town.
“I haven’t seen it,” he said. “But beech canker is bad all across Northwest Connecticut. And this year, we got hit really hard with gypsy moths.’’
Beech leaf disease first showed up in Ohio in 2012. It moved east and also jumped across Lake Erie into Ontario.
Marra said when scientists first found it, they had no idea what was causing it.
“They were looking at bacteria, at fungi,’’ he said.
By 2019, they’d found the culprit — a nematode, Litylenchus crenatae, subspecies mccannii.
Nematodes — aka roundworms — are among the most abundant creatures on the planet, with 25,000 species identified and thousands more yet to be discovered.
They can vary from 23-foot long parasitic roundworms that live in sperm whales, to the hookworms and roundworms you take your pets to the vet to treat.
Some nematodes are beneficial, killing garden pests. Others live in the soil and are crucial to soil decomposition. But some are pests themselves.
The beech leaf nematodes are microscopic. Marra said they get into beech leaf buds in fall and winter, feeding on and damaging the buds.
Leaves from infected buds sprout with the brown stripes already on them. The leaves drop prematurely, weakening the tree and leaving it susceptible to other diseases. In a few years, the tree can die from the infestation.
Marra said the nematodes may damage saplings and young trees more than mature trees.
What researchers don’t know is how the nematodes — native to Japan, Korea and Southeast Asia
— got here to begin with. Nor do they know they spread so quickly.
Marra said rain and wind could spread the nematodes throughout a tree or from one tree to a neighboring tree. But big jumps — from one town to another, from one state to another — are harder to explain.
“Maybe it’s birds, maybe it’s insects,” he said.
The infestation has the potential to be horrible for forests in the northeast as well as the stately European beeches that shade town parks.
Beech trees are — after oaks and acorns — the greatest providers of food to forest dwellers. They’re also trees that can grow in shade. They’re considered a climax species.
Chris Martin, of DEEP, said that by numbers, beech trees rank third in the state, with 57 million beeches in the state.
“If they lose the beeches, where will black bears turn to for food?’’ he said. “I think we’ve seen the answer to that.’’