Scientists: Beech Leaf Disease, potentially fatal for trees, widespread in CT

Photo of Ben Lambert
An example of Beech Leaf Disease.

An example of Beech Leaf Disease.

Connecticut Agricultural Experiment Station

NEW HAVEN — A potentially fatal disease for beech trees has become widespread in large parts of Connecticut, and is no longer novel, according to Connecticut Agricultural Experiment Station scientists.

Beech Leaf Disease, first detected in the state in 2019 in lower Fairfield County, now is widespread and prevalent on American beech trees (Fagus grandifolia) throughout Fairfield, New Haven, Middlesex and New London counties, and appears to be spreading into Litchfield, Tolland and Windham counties, as well, CAES officials said in an email.

Robert E. Marra, an associate scientist/forest pathologist in the Department of Plant Pathology and Ecology at CAES, said it is not known for sure how many beech trees are affected by beech leaf disease in Connecticut, “but it is worth noting that the difference between last year and this year is dramatic, especially in these four lower Connecticut counties.”

“If you ask property owners in Fairfield, New Haven, Middlesex, and New London Counties, they would say that nearly all their beeches have beech leaf disease,” Marra said. “However, while we haven’t been able to survey all our state forested lands, it seems that there are pockets of severe outbreaks, and stands where we see little if any BLD.”

Marra also noted that, according to the U.S. Forest Service’s inventory data (from January 2021), the American beech is the third most abundant tree species in Connecticut, after red maple and black birch, and is found in just over 40 percent of the state’s forested lands. He said from these data, it can be estimated that Connecticut has about 57 million beech trees throughout the state.

CAES officials said the disease, “which can kill trees within several years of detection, was first discovered in 2012 in Ohio, followed in subsequent years by detections in Pennsylvania, New York, and Ontario, Canada.”

The disease, typically “characterized by dark striping between leaf veins” on beech foliage, as observed looking up into the canopy, has been particularly severe this year.

The intensification was potentially driven by a hot and dry summer last year and a dry spring this year, according to CAES officials.

“(This year’s symptoms) can include: aborted leaf enlargement; cupping, browning, and yellowing of foliage; branch and tip dieback; and in some cases, premature leaf drop,” officials said.

The tree disease appears to be spreading, “particularly from west to east based on the number of new county detections in 2019 and 2020,” in the United States, according to the U.S. Department of Agriculture Forest Service. “Insect or avian vectors as well as human-mediated movement of the nematode are possible modes of its dispersal that are currently being studied.”

The disease is caused in American, Oriental and European beech trees by the foliar nematode, officials said.

It has become common enough, as widespread occurrence of BLD has been well-documented in 2021, that “reports of BLD in Fairfield, New Haven, Middlesex, and New London Counties to CAES and DEEP are no longer requested” from the public, officials said.

CAES scientists, along with federal staffers and researchers in Ohio, Pennsylvania, New York and Ontario have joined together to study the disease’s development and transmission, and possibilities for controlling it, officials said.

According to a report by Dr. Yonghao Li of the CAES and shared by the state Department of Environmental Protection, “little is known about the biology of the pathogen and epidemiology of the disease,” and “no effective control or eradication measures have been developed.”

Further, according to Li, “the spread of invasive species can be prevented by restricting the movement of plant materials and monitoring trees closely for signs and symptoms.”

Li noted that quarantines and regulations could be used to prevent further spread of the disease and that “management efforts for the disease should focus on preventing the introduction of this invasive pathogen.”

According to the federal agriculture agency’s forest service, there also is “likely a delay between initial nematode infestation” and detection of the Beech Leaf Disease as the Litylenchus crenatae “has occasionally been confirmed in asymptomatic tissue at the molecular level.”

“Tree mortality of all age classes has been occasionally observed within 2 to 7 years but appears to be more common for smaller trees,” the agency reported.