Oak Wilt or Bot Twig Canker?

A year after the derecho, we lost so many beautiful trees while others lost limbs. We always remind oak lovers to avoid unnecessary pruning from April to July to minimize the risk of Oak wilt transmission. We had questions at the Plant and Insect Diagnostic Clinic from oak caretakers wondering if their derecho injured trees may be infected with oak wilt after the derecho.

We hope the insect population that vector of oak wilt was low last August, as the risk of vector transmission is considered low from July to October, but we are not sure. Oak wilt transmission is dependent on insect population (abundance) and weather. 

Many inquiries with concerns of oak wilt instead show the symptoms and symptom distribution in the tree that match Botryosphaeria twig canker. To learn more, see the video below and page 10 on this US forest service publication, How to recognize common diseases oaks.

If you want to have your tree assessed through digital photos, See our tips on taking and sharing photos at our page https://hortnews.extension.iastate.edu/pidc/digital-photography. Submit your plant problem image request at (Plant Problems - Diseases) form.

Testing for oak wilt requires a specific sample to avoid false negatives; see or Vascular wilts testing page. To learn more about oak wilt, see our encyclopedia article and page 12 on this US forest service publication, How to recognize common diseases oaks.

Authors: 

Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician

Dr. Lina Rodriguez-Salamanca is a diagnostician and extension plant pathologist with the Iowa State University Plant and Insect Diagnostic Clinic  (clinic.ipm.iastate.edu), a member of the National Plant Diagnostic Network (NPDN, ...

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