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How to Get the Most Out of a Plant Problem Diagnostic Sample

Posted by Blythe Howell | February 28, 2019

While it may not look or feel like the growing season is around the corner, soon enough it will arrive. With the growing season comes the growing problems such as diseases and pests so what should you do if you find a problem and would like a confirmation or diagnosis of the issue? Send it to the Plant Pest Diagnostic Clinic in Pullman! To get the best diagnosis possible here is information on how to prepare the best diagnostic sample possible.

First, download a sample submission form (pdf).

The form will walk you through what type of information is helpful for diagnosis.

The first sections of the form will pertain to plant information such as the variety. With the amount of small grains and agriculture in our region, we have a wide range of varieties with very different traits that impact the plant’s response to different stresses. We also ask about the symptoms observed on the plants to ensure your concerns are appropriately addressed.

Make note of the pattern of damage at the site (i.e. field). Is the damage wide-spread, localized to a single area or a few areas? Are there site factors that influence the pattern such as field borders, wheel lines, roads, or changes is topography? Photos can be extremely helpful in communicating patterns seen at the site. Other information regarding the site includes soil characteristics. It is well known that soil properties such composition and pH have a big impact on plant health.

Inputs to the site such as fertilizer, insecticides, fungicides, etc. and the time of their application are important. Some pesticides can impact our ability to recover pathogens from the tissue or may explain why we see the damage of a pest but not the pest itself. Further, there can be interactions with chemicals and weather resulting in damage so this information helps tease apart what symptoms can be attributed to different causes.

The last section to the submission form asks ‘What do you think is wrong?’ this is not laziness on the part of the clinic but an acknowledgment that as the grower or the person in charge of the sample you have an understanding of previous issues in the field or the progression of the damage.  This is also a good place to instruct the diagnostician if you have a particular concern you’d like tested, such as a viral disease!

After the submission form is the handling of the sample. Truly, a good and accurate diagnosis depends on the quality of the sample. To ensure good sample quality collect the sample the same day you are to send it through the mail or plan to drop it off at the clinic. If this isn’t possible store the sample in the refrigerator but do not allow it to freeze. Keep in mind that the longer a sample is out of the ground, the more likely it is to rot. The sample should be collected into a plastic bag with no additional moisture added. Plastic is preferable to paper as it keeps allows the plant to retain natural moisture without rotting. Rotting of samples most often occurs when water is added to a sample; this encourages secondary organisms like fungi and bacteria to contaminate potentially important tissues. Whole plants are preferred whenever possible. Ideally, the roots and a small amount of soil surrounding the roots are to be placed into a separate plastic bag and taped to limit the amount of soil that gets onto the leaf tissue (see photo) then the whole plant should be placed into a second plastic bag and sealed. If the plant is large or singularly valuable call the diagnostic clinic to discuss how best to sample.  Send the sample as quickly as possible to prevent decay during transportation.

Be aware that samples sent on a Friday will not arrive until after the weekend which can result in the degradation of the sample quality.

Soilborne wheat mosaic sample packaging.
Soilborne wheat mosaic sample in a plastic bag.

Rachel Bomberger.
If you have questions please contact the diagnostician, Rachel Bomberger, via phone at (509) 335-3292, via email at or visit the Plant Pest Diagnostic Clinic webpage.

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