Correct Sample Submission for Plant Disease Diagnosis
How not to send a sample: Bag an entire plant in a tight ziploc bag with moistened paper towels so that there is 100% chance that the plant will turn to mush.
As the new growing season starts, plant diseases will begin to show up. In order to provide a correct diagnosis, samples submitted to the diagnostic lab must be of good quality. Here are a few guidelines for sample submission:
For turf samples: Cut a 3 by 3-inch square of turf that includes both healthy and diseased looking plants. Put the sample in a plastic ziploc bag without a moist paper towel and send overnight to the Utah Plant Pest Diagnostic Lab.
For soft-tissue samples (annual plants, vegetables and fruit): Put symptomatic plants in a plastic ziploc bag without a moist paper towel and send it either the same day or the next day. Do not refrigerate or store the collected samples for more than one day. Do not send the samples in a paper bag as they will dry out and may make a diagnosis impossible.
To prevent the above from happening, the ziploc bag or plastic should be wrapped around the roots only, leaving the top part of the plant (with the symptoms) exposed and dry.
For all samples: Fill out the sample submission form on the Utah Plant Pest Diagnostic lab website with as much information as possible. This can help us narrow down possible causes of the problem. Include all pesticides, including herbicides, that were sprayed, irrigation type and frequency, age of the plants, symptom description, etc. If possible, e-mail images of at least 3 views: a wide view showing the affected plant/area plus the surroundings; a closer view of just the affected plant/area; close-ups of the symptoms.
Make sure to correctly address the package to the diagnostic lab. The address is:
Utah Plant Pest Diagnostic Lab, Utah State University,
5305 Old Main Hill, Logan, UT 84322
If the package is addressed to the USU Soils Analytical lab, the sample will be delayed by several days and its quality for diagnostics may be reduced.
To avoid tissue deterioration to the point that we may not be able to identify the cause, it is best to send the sample overnight. We have received samples in the past that were kept in a refrigerator (or left in the car) for several days before shipping and we could not tell what kind of plant it was, let alone identify the problem.
In those cases, we have to request another sample, which will delay identification of the problem and recommendation for treatment. If moist paper towels are included in the Ziploc bags, the additional moisture can result in quick development of mold that may make it impossible for us to identify the original problem.
Time frame for diagnosis: Many samples cannot be diagnosed by looking at the sample under a microscope alone. We may have to culture bacteria or fungi or run tests for virus diagnosis. Fungi do not grow very fast and it may take five days to a week before we can identify a fungal pathogen. Bacteria grow faster but often need additional processing for identification. In that case, we will be able to give you a preliminary identification that will be followed by a confirmation one to two weeks later.
- Claudia Nischwitz, Plant Pathologist