Hundreds of ornamental pear trees in the Rockville Centre downtown...

Hundreds of ornamental pear trees in the Rockville Centre downtown business district are rotting as a result of a difficult-to-treat fungus, seen here on Thursday, Sept. 21, 2017. Credit: Newsday / J. Conrad Williams Jr.

Ornamental pear trees generously planted throughout Long Island are rotting as a result of a contagious, difficult-to-treat fungus, horticulturists say.

“We’ve got hundreds of them that are dying,” said Rockville Centre Mayor Francis Murray. “It might even be a couple of thousand.”

Murray said the village has a diverse tree population, including oaks, pines and maples, but the ornamental pear trees are suffering from a disease known as pear trellis rust.

Pear trees have been planted for decades around the Northeast on both public and private property. Their white flowers and 20-foot average height made them suitable for planting in downtown areas, especially since they fit under power lines, according to Vincent Drzewucki, an urban forestry and horticulture educator with the Cornell Cooperative Extension of Nassau County.

The trees were imported from Asia in the 1960s and ’70s. They were over-planted, Drzewucki said, and that has contributed to the scope of the problem.

“They were very tolerant of urban conditions, and they were relatively pest-free at the time,” he said.

But trellis rust spread across Nassau and Suffolk counties, as well as upstate New York and parts of Connecticut, within the past 10 years, Drzewucki said.

Symptoms begin as yellow-orange leaf spots, which then develop into infectious spores in late summer. The fungus lives and grows on the leaves of deciduous trees, and then spreads to other host plants, allowing it to survive through the winter. A single leaf can easily transfer infected spores to other trees, or the disease can be transferred if the roots of several trees are touching, research shows.

Horticulturalists for several years have not recommended ornamental pear trees for planting, Drzewucki said.

Harsh urban conditions — poor hydration and fertilization, and compact soil with low oxygen levels — in downtown areas contribute to the overall poor health of the trees, which can make them susceptible to illness, he said.

“It was very popular back in the day because it was a faster-growing tree,” said Peter Colgan, an International Society of Arboriculture-certified arborist and the owner of Kings Park-based Colgan Tree & Landscape Service Inc.

“It’s very, very hard to control,” he said of pear trellis rust. “And sometimes, it’s not cost-effective.” Fungicides can be sprayed to stunt the spread of disease, but they are often expensive, Colgan said.

Areas of Long Island are still replacing trees lost in superstorm Sandy, which Colgan used as an example of how smart tree-replacement choices should be made. Colgan said his company advised a replacement effort that began Sept. 14 in East Rockaway for hundreds of sycamore trees destroyed by the storm. They are to be replaced with zelkova trees, which Colgan said are more saltwater-resilient and have short, thick trunks.

“You have to go by the environment where the trees are going to be planted,” Colgan said.

Added Drzewucki, “Municipalities either don’t do their homework or don’t reach out to those who know.”

Pear Trellis Rust

Caused by the rust fungus Gymnosporangium sabinae.

Common in Europe and parts of Canada.

Found in the Pacific Northwest in the late 1990s and in Michigan in 2009.

First confirmed in New York State in 2011.

Can cause losses in pear crops and impact the health of ornamental pear trees.

Source: University of Connecticut

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