Oak wilt was discussed in issue No. 7 of this newsletter. Many readers have submitted wood to the Plant Clinic to have it cultured for the pathogen that causes oak wilt. In many cases, we have confirmed the presence of that disease. In many others, however, symptoms are typical, but we do not isolate the fungus. I believe that this has to do with the shipping conditions.
We highly recommend that you send oak wilt samples packed in ice. The oak wilt fungus is very sensitive to heat and often dies in transit at this time of year. If the fungus is dead, it will not grow in our cultures, and we will report that the fungus was not present in the sample. If the sampled tree does have oak wilt, this will result in a false negative. All southern state clinics require that samples of oak arrive on ice. For best results, this is my suggestion for Illinois clients as well.