Collecting Samples for Vascular Wilt Testing

Oak wilt, Verticillium wilt, and Dutch elm disease are examples of vascular wilt diseases. The fungi that cause these diseases impair the treeÕs ability to conduct normal water flow, causing the classic wilting symptoms. Field diagnoses of vascular wilt diseases can be difficult, making it necessary to have an accurate laboratory diagnoses to determine proper management. There are a few easy collection guidelines that will help diagnosticians make an accurate diagnosis.

  1. The best samples are collected in spring (May-June) or fall (September) when the fungus is most active, although it is still possible to detect the wilt fungi during the summer months.
  2. Send branch samples from at least 3 different areas in the crown that exhibit the vascular wilt symptoms.
  3. Branches samples should be 6-10 inches long and 1/4 to 1/2 inch in diameter and taken from areas that show wilt symptoms.
  4. The branches must be living when sampled in order to detect the vascular wilt fungi.
  5. Seal the samples in plastic bags and keep them cool and dry prior to shipment. The samples should be shipped immediately.

The success of the laboratory diagnoses is dependent on the quality of the sample. Following these collection guidelines increases the chance of detecting the vascular wilt fungi.

This article originally appeared in the July 21, 2000 issue, p. 95.

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