Oak stress was a topic of the most recent issue of this newsletter. Anthracnose, oak wilt, and bacterial scorch are diseases that should be considered when evaluating an oak problem. Information on them can be found in issues 3, 5, 11, 13, and 17 (2002). This year, the Plant Clinic has received many complaints of oak stress, particularly in the northern parts of the state.
Some of you have asked where we have seen oak wilt. We have confirmed isolation from samples in Carroll (13 instances), Cook (2), DeKalb (1), DuPage (1), Lee (2), Madison (2), McHenry (1), McLean (1), Tazewell (1), and Woodford (1) counties. The high number in Carroll County came from one forested area.
Bacterial leaf scorch is not something that we can confirm in this lab. We sent pin oak samples from Champaign County to AGDIA, Inc., for testing. We have four confirmed cases of bacterial leaf scorch on pin oak. Recently, I received a call from an arborist in JoDaviess County who sent a bur oak sample to AGDIA and received a confirmation of bacterial leaf scorch. We do have the disease in Illinois, but we do not have a handle on its distribution.