Oak Wilt Fungus and Emerald Ash Borer Persist

Sep 14, 2012

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Local parks organizations are trying to inform homeowners about the dangers of two of the greatest threats to the region's trees.  A series of informational meetings about controls for oak wilt fungus and the emerald ash borer have been held in Allegheny County.  

Oak wilt is caused by a fungus that primarily kills red oaks but can also affect white oaks.  Sap-feeding beetles spread the fungus through fresh cuts during spring and summer, according to Denise Schreiber, Greenhouse Manager for Allegheny County Parks, so pruning should only be done when the tree is dormant, well after the first frost in late fall and before March or April.  Pruning tools should be sterilized after use to prevent spreading the fungus.

The fungus that causes oak wilt, for which there's no cure, also spreads through adjacent root systems.  Since preventive injections have had limited success, Schneider said the emphasis is on containment.  Infected trees should be removed when they are dormant, and Schneider said spread of the fungus can be prevented by cutting roots 3- to 4-feet deep all around an infected tree that is being removed, along with burning or safely disposing of all trimmings.  Infected trees have been removed in Frick Park.  Schneider has seen oak wilt in South Park and Hartwood Acres, as well as residential neighborhoods.  Signs of oak wilt include leaf fall in June, a thinning crown and bark falling off, which can spread the fungus and should be disposed of by burning or burying.

The emerald ash borer got to the U.S. somehow from Asia and will eventually kill all the country’s ash trees, according to Schneider, though there is a treatment that can protect a tree for two years at a time.  It can only be purchased by licensed pesticide operators and requires special equipment for injecting into trees.  The Pennsylvania Department of Agriculture is trying to slow down the advance of the emerald ash borer by mandating that firewood not be transported from county to county, but Schneider said it is all over the state and has gotten to West Virginia and Tennessee.