Jul 30 2013
I love trees so much that I jump at the chance to learn more about them.
Back in February 2011 I learned about the threats facing 60% of our city park trees when the Pittsburgh Parks Conservancy presented a public event called Preserving Pittsburgh’s Trees: Action and Recovery. I was already familiar with emerald ash borer since I first saw it in Schenley in May 2010 but I learned about something I’d never seen before: oak wilt.
While Schenley Park had been coping with the death of all its ash trees, the other three big parks — Frick, Highland and Riverview — had experienced oak wilt as well.
Oak wilt is caused by a fungus that doesn’t spread easily but can kill a tree in 30 days. The fungus travels in the oak’s vascular system and when the tree detects it it blocks those vessels. The blockage kills the tree. It’s the arboreal equivalent of a stroke. Watch the 13 minute video here to see how this happens.
After the conference I began to watch Schenley’s oaks with new interest. Two years passed. Early this month I could tell something wasn’t right at Prospect Circle. I emailed this and other photos to Phil Gruszka, Director of Park Management and Maintenance at the Pittsburgh Parks Conservancy, and he confirmed that oak wilt had struck again. He also started the ball rolling to eradicate it.
Fortunately the fungus spreads slowly and that’s the key to stopping it. It’s either carried into an open wound by sap-eating beetles (this is harder than you think) or it travels from oak to oak via root grafts. Amazingly, the roots of adjacent oaks graft to each other when they touch underground. In a pure oak stand they become one huge vascular system.
There is no cure but future deaths can be prevented by cutting down the affected trees, trenching the perimeter to prevent uninfected roots from entering the danger zone, and medically treating the oaks just outside the perimeter.
In the not too distant future a large patch of dead and dying oaks will be chopped down at Prospect Circle. This will look ugly at first but will save all the other beautiful oaks along the road and hillside.
For more information about oak wilt, read these Pittsburgh Parks Conservancy blogs about the episode in our parks in 2010:
- From Loss to Opportunity (Frick)
- Medicine For The Trees (Frick)
- Oak Wilt Continues to Spread (Highland and Riverview)
(photo of the oak wilt trees in Schenley Park, July 2013, by Kate St. John)
UPDATE on 18 October 2013 from the Pittsburgh Parks Conservancy –> click here.