Submitting samples for vascular wilt of woody ornamentals

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Woody ornamental vascular wilt diseases such as Verticillium wilt, Dutch elm disease and oak wilt can be frustrating, not only for our clients but also for lab staff. They can be challenging to diagnose and downright impossible without a quality sample. The accuracy of results relies heavily on the sample itself. Improperly collected, stored, or shipped samples decrease the chances of isolating a pathogen. Following the procedures outlined below will help to ensure sample quality and increase the likelihood of an accurate diagnosis.

  1. Select branches that are partially wilted, with symptomatic leaves progressing from the tip of branches inward to the trunk. Be sure that branches are not totally wilted, dry or dead. Check sapwood for discoloration by removing a small section of bark. Discoloration appears as gray to green streaks. Discoloration is not present in all species of trees; however its presence greatly increases the chances of isolating the fungus.
  2.   Select samples from up to three symptomatic branches per single tree. It is critical that the sapwood is moist to the touch. Avoid collecting samples from the extreme tips of branches: this tissue wilts first and is often too dry for successful isolation.
  3.   Branch samples should be at least one inch in diameter (when possible), cut into six to eight inch lengths, and placed in large resealable plastic bags. Do not add moisture to the bag. Smaller diameter branch samples are acceptable only if the sapwood is moist, and samples have been kept cool.
  4.   Keep samples cool during sampling, shipping, and storage, but do not freeze. Never leave samples un-refrigerated or exposed to direct sunlight.
  5.   Ship samples by overnight mail or deliver in person to the laboratory. And, as always, do not ship samples on Friday.
  6.   You may not be able to follow all of the guidelines for every sample. The most important guideline to remember is to collect samples from live, symptomatic branches. If the sample would make good kindling, it probably isn’t going to be acceptable for vascular wilt testing. If you’re not sure what kind of sample to submit, feel free to contact the lab at (517) 432-0988.

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