Pathologists Corner – Oak Wilt

Oak wilt is caused by a fungus (Ceratocystis fagacearum) which colonizes the vascular system of the tree.  Conduction of water is disrupted causing the leaves to wilt and ultimately for the tree to die.  The disease is highly virulent and spreads in two (2) known ways.  Trees which have formed root grafts with infected trees may themselves become infected through root graft transmission.  For this reason entire stands of Oak forests may be destroyed over a period of time.  New Oak wilt infection centers may begin when a small sap feeding beetle (aka Nitidulid) visits a spore mat on an infected Red Oak.  (Live Oaks do not produce spore mats).  Once the insect has visited a spore mat, his body may carry the fungal spores to a fresh wound, thus creating a new Oak wilt center infection.  The sap feeding beetles are attracted to feed on the sap which oozes from fresh wounds on trees.  Sap feeding beetle activity, spore formation and tree susceptibility are all at high levels from February to June.  For these reasons the Oak wilt control strategy involves the following recommendations:

1. Avoid pruning mid February – mid June (Red Oaks and Live Oaks).
2. If you must prune during this time, paint cuts and wounds as soon as possible after they occur.  The sap flow from wounds usually has stopped within 24-48 hours, therefore, old wounds do not require painting.
3. Healthy trees near Oak wilt infection centers may be treated on a preventable basis with the fungicide “Propaconizol” (aka Alamo).  This fungicide is injected into the tree at the root flares, and can protect trees for up to three (3) years.
4. Once trees have become infected, successful therapeutic treatment with Alamo is possible, however, results vary and most trees will not survive once symptoms develop.
5. Infected trees, particularly Red Oaks, should be removed promptly.  Red Oak firewood may be another means by which the fungus may be transported to new areas.

Additional research is needed to solve the biology regarding the overland transmission of this potentially devastating tree disease.

More information is available concerning Oak wilt through the Texas A&M extension service, the Texas Forest Service

If you have any further questions or suspect you may have Oak wilt please give us a call or fill out a QUICK contact form!

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