Oak wilt is a lethal fungal disease that causes oak trees to show leaf discoloration and overall wilt. Red oaks are more susceptible and are killed faster than the more resistant white oaks. This disease is spread most efficiently through root grafts, but also is spread by insect vectors.
A proper sample allows for successful isolation of the fungus and accurate diagnosis of the disease. Samples should be taken from dying, but not dead or dry wood. The ideal size of the branches sampled is approximately one half inch to one inch in diameter. The submitted sample should be placed in a plastic bag and include several branches from different areas on the tree showing leaf discoloration. Also include a leaf sample, so the species of oak can be determined.
The samples should be kept cool. It's best to ship the samples by overnight mail or deliver in person. The lab process of isolating this fungus normally takes two to four weeks before results can be obtained. There is a $10 laboratory fee.
Samples can be submitted through your local county extension office, or delivered directly to the Plant Disease Clinic. Plant Disease Clinic
323 Bessey Hall
Ames, IA 50011
This article originally appeared in the 7/2/2004 issue.