Frick Park Trees Fight Fungus

Oak wilt, a potentially fatal fungal disease spreading through Frick Park, recently was identified in a strand of trees near a popular mountain-biking trail.

The location, known to cyclists as “the roller coaster” because of its series of ravines, is near Fire Lane extension off of Hutchinson Street in Regent Square and is the third spot in Frick where oak wilt has been found, according to Phil Gruszka, Pittsburgh Parks Conservancy parks maintenance and management director. Two other sites have been treated.

“We’re marshaling funds to treat a dozen or less trees that are symptomatic in this area,” said Gruszka, whose organization is partnering with the City of Pittsburgh and the Pennsylvania Department of Conservation and Natural Resources’ forestry bureau to treat oak wilt and other diseases and pests impacting the park’s native woods. 

“It will be the city’s decision, but our preference is to remove the infected trees and treat healthy trees beyond the infected site,” he said.

Four years ago, about 100 affected trees in a two-acre site near the intersection of Kensington and Hawthorne trails were removed and their roots were severed by a trenching machine to prevent oak wilt from spreading. About 30 nearby healthy oaks were injected with fungicide as a preventive. 

Interpretive signage was erected near the site to explain the disease and the treatment, Gruzska said.

“The Fire Lane site looks like how Kensington looked four years ago," he said. "Oak wilt is controllable with the right procedures and protocols, but if you don’t do something, it will go from a small site to a large site pretty quickly.” 

Oak wilt kills by preventing trees from translocating water, food and starches. Symptoms surface in early to mid-summer when trees are in full canopy, said DCNR service forester Michael DiRinaldo.

“The tips of the leaves start to turn brown and it works its way down to the root system," DiRinaldo said.

All species of oak are vulnerable, although those in the white oak family withstand wilt longer before they actually die, while red oaks, scarlet oaks and pin oaks can succumb within weeks, DiRinaldo said.

And the disease is highly transmissible.

“Picnic beetles are attracted to fresh wounds on a tree," he said. "If a tree gets bumped with a lawn mower or hit with a back hoe, beetles will feed on the sap. If they’re carrying oak wilt fungal spores, they’ll directly inject them into the tree.”

The loss of even one tree impacts the entire forest because it retains at least 500 gallons of storm water a year. That’s a big deal in the where, despite completion of a $12 million restoration project of the run and its floodplains, runoff remains a problem.

After heavy downpours, the run gets flooded, and it would be much worse without trees.

“The oaks are in the upper regions of the hillside, where you really don’t want to lose them, because of the potential of erosion," DiRinaldo said. "They help hold in the soil.”

Oak wilt isn’t the only problem in the Frick forest. Emerald ash borer also is taking a toll. Many of the park’s green and white ash trees have been treated for the pest, but the insect has prevented ash seedlings from sprouting in spots where diseased and invasive species, such as Tree of Heaven, have been removed.

“Ash are generally the first to jump up when you remove other vegetation,” Gruzka said. “That hasn’t happened, but we’ve planted maples, cucumber magnolia, hackberry, and linden trees and we’ll see what takes over that role."