The red oak family could face devastating losses if a fast-spreading fungus called oak wilt is not controlled, local arborists say.

For the past 15 years, oak wilt has affected the Midwest, Pennsylvania, West Virginia, scattered parts of the South and Texas.

Locally, several stands of trees that include oaks with wilt have been identified. In April, two acres of oaks were removed from Frick Park. Several oaks in Highland Park and South Park were symptomatic last year and will be confirmed this week, said Phil Gruszka of the Pittsburgh Parks Conservancy.

A string of drought years can make red oaks susceptible to organisms that become pathogenic because the trees are stressed. These organisms under balanced climate conditions would not normally become deadly, he said.

Whether a few wet seasons could be a remedy depends on the side you take, he said: Some scientists believe the fungus was introduced; others believe it is native.

Native diseases affect plant health some years and not others, when the tree can rebound, he said. "It's the non-native diseases the trees have no defense against.

"I am of the mindset that this is an introduced pathogen," he said. "I don't believe several rainy seasons will make this disease go away."

Sap beetles can carry the fungus to a wound in an uninfected tree, but the most common transmission is from tree to tree by underground root grafting the trees do themselves, he said.

Mike Gable, deputy director of the Department of Public Works, said trenches were cut in Frick Park to prevent the roots of the removed trees from grafting onto the roots of other trees.

"The city has been aware of the problem and is monitoring" trees in all four RAD-funded parks -- Frick, Schenley, Riverview and Highland, he said. "We will continue monitoring, and we are ready to replant to reforest the cleared areas" with Regional Asset District funds.

Research in arborist journals reports the fungus was identified in this country in 1944 but has spread mostly since the 1980s with the development of housing in oak forests. Tree wounds are the entry point.

Oak wilt is particularly aggressive among red oaks, capable of destroying them within one growing season. It can kill white oaks but takes longer.

The red oak group includes pin oaks and scarlet oaks.

Mr. Gruszka said the conservancy is a week or two away from having specific data on the oak population in the four RAD-funded parks.

The city contracted a recent tree inventory in those parks and counted a total population of 373,000 trees. The final report "will give us a good indication of how significant the disease will be. We're certain it's going to be significant," he said.

"We know with the emerald ash borer that 16.7 percent of trees in our natural areas are ash, and that means about 50,000 trees are going to be lost. Add oak wilt to that and you are looking at a significant change in the native tree population."

The most obvious sign of oak wilt to the layman is dried-up green leaves floating to the ground in the summer.

"In Frick Park about three years ago, there were some dead [oak] trees but there were not other symptoms. Last year, when we saw green leaves falling off the trees, we knew. It had gone from a handful of infected trees to two acres.

"It's potentially fatal to all our oak trees and will sweep its way throughout the area if it's not contained."

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