New Jersey forestry officials are completing a study of an incurable insect-borne disease that is killing the northern red oak, the state tree, and has spread to other species throughout the region.
Bacterial leaf scorch first turned up in the state in Moorestown, Burlington County, in the late 1980s. The scourge, which some fear could prove as destructive as Dutch elm disease was a decade ago, is now widespread among oaks in South Jersey and eastern Pennsylvania - and is on the move.
"It seems to be spreading north and east," said Ann Gould, a plant pathologist at Rutgers University in New Brunswick. "I've seen a lot more of it this year than I ever have before."
The disease has been found as far north as Sussex County in New Jersey and as far west as York County in Pennsylvania. It has yet to be detected in coastal regions or along the New York-New Jersey border, Gould said.
The bacteria that cause leaf scorch, Xylella fastidiosa, clog a tree's xylem, the vessels that carry water from the roots to the canopy. The effect, experts say, can be compared to the clogging of arteries, and the disease, in essence, starves a tree of water.
"It plugs them up," Gould said.
Because leaf scorch tends to manifest itself in late spring and early autumn and produces a brown discoloration on leaves, the symptoms are often confused with those of heat stress and the coming of fall.
Leaf scorch is spread by insects that feed on the trees, but researchers are unsure what species are responsible or why the disease proliferates in populated areas rather than in forests.
"I think it has us pretty concerned," said Hal Rosner, an arborist with Bartlett Tree Experts in Bala Cynwyd, which serves the Mount Airy and Chestnut Hill sections of Philadelphia and parts of Montgomery County. "I would say that between 20 to 30 percent of the trees I look at, and I mean oak, are infected."
One downside of the disease, Rosner said, is that homeowners do not always replace affected oaks with equally majestic species.
"The big grand pin oak in the front yard will be replaced with an ornamental pear tree," he said, "nothing as grand or statuesque as an oak."
Alan Iskra, a plant pathologist with the U.S. Forest Service in Morgantown, W. Va., said officials had once thought leaf scorch was isolated to New Jersey but were now concerned about its spread in Maryland, Delaware, and the Washington, D.C., area.
"This is going to be a toughie to control," Iskra said. "It's a chronic disease. It's going to be as big as Dutch elm disease and probably even bigger."
To some in the New Jersey forestry community, Cliff Pfleider of Moorestown's Department of Public Works is the state's "godfather of bacterial leaf scorch."
It was in 1987 that Pfleider noticed the chronic decline of oaks in Moorestown and their resistance to traditional treatment. He alerted state and federal forestry officials, who have been working on the disease ever since.
According to Pfleider, leaf scorch starts with a few dead branches and kills slowly, sometimes taking five years.
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