Beech trees at Oyster Bay's historic Planting Fields Arboretum are...

Beech trees at Oyster Bay's historic Planting Fields Arboretum are under attack by life-threatening diseases, according to a national report put out by the Washington D.C.-based Cultural Landscape Foundation. Credit: Planting Fields Foundation

The beech trees that grace Oyster Bay’s Planting Fields Arboretum State Historic Park are at risk due to two life-threatening diseases — including one that’s proved “startling” and very difficult to treat, according to a national advocacy organization.

The stately trees with wide canopies were part of the original arboretum planted by the Olmsted Brothers, designers hired by the estate's onetime owner, William Robertson Coe, more than 100 years ago to shape his grounds. The brothers were the son and stepson of Frederick Law Olmsted Sr., considered the father of modern landscape architecture and designer of Central Park and Prospect Park.

But now there is concern about the effect of diseases that have spread elsewhere in the country and attacked the dozens of beech trees among the hundreds growing within the historic park, according to the Washington, D.C.-based Cultural Landscape Foundation.

Phytophthora bleeding canker and Beech Leaf Disease “pose an imminent threat to both species of beech at Planting Fields,” according to a national report put out by the foundation.

“The former can be treated effectively when detected early, but the volume of blighted beech trees on the property, combined with accessibility challenges posed by the site’s dense woodlands, make large scale treatments prohibitively expensive and impracticable,” the foundation wrote in the report issued Tuesday morning.

Infestation by the disease causes changes to foliage, such as striping, texture changes, curling and loss of leaves.

“At Planting Fields, this disease is progressing at a startling rate,” the report said.

“Daily monitoring and image capturing reveals that more than half of the total number of beech trees, both natural and cultivated, have been affected. In the spring of 2022, a majority of beech trees failed to leaf out, and those that did had lost up to 80% of their leaf canopy,” the report said.

The state Office of Parks, Recreation and Historic Preservation did not comment.

Oyster Bay isn't the only place tree ailments are putting historic trees at risk. Ash trees, long the source of baseball bats, are in such danger from invasive insects that there might not be one ash bat used in the postseason, The New York Times reported last week.

Beside being culturally significant and a draw to visitors at the Oyster Bay site, the beech trees are habitats to numerous insects — such as pollinators; the nuts that the trees produce provide an important source of nutrients for wildlife, the report noted.

Donna W. Moramarco, a historic landscape horticulturist with the Planting Fields Foundation, said in a message that Phytophthora bleeding canker has existed on the fields’ beech trees for several years and is treatable with fungicides. It manifests as “cankers with black staining on bark areas of the tree,” she wrote.

But Beech Leaf Disease “is a new problem” at the fields, first identified there in 2021.

“It does not necessarily attack the entire tree at once. The canopy can be affected, while other parts appear unaffected. It does not discriminate with age of the tree — young, middle-aged, and mature trees can all be affected by BLD,” she wrote, using an abbreviation for the disease.

She said that the disease is carried by a nematode parasitic worm and has spread from where it was originally detected, in northeast Ohio, 10 years ago, to 10 other states and Canada.

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