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. 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.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on August 13, 2021. The information contained within may not be the most current and accurate depending on when it is accessed.