Let's say your tomato plants have dark, weepy sores. Or the rhododendron leaves along your house are yellow and droopy. Perhaps you'd like to know what that gray, sticky gunk is on your honeysuckle buds.
If you bring a sample of a diseased plant to a county office of the Oregon State University Extension Service, a Master Gardener™ or home horticulture agent will try to answer your question and diagnose the problem. If the problem is too tricky to diagnose by simple means, they will ask if you would like your specimen sent to the OSU Plant Clinic on the Corvallis campus, along with the information you provided. (Note: This clinic is a fee-based service so you would be billed.)
For best service, when collecting a specimen to bring to your local county Extension office, follow the guidelines below.
Select plant material showing the symptoms you are concerned about. If possible, also bring in a healthy sample to compare it to.
For small plants, bring all parts of the plant, including roots and soil when possible. Enclose the roots and soil in a plastic bag. If it is not practical to bring in an entire plant, include as large a section of the affected plant part as possible. For example, if a branch is showing symptoms, cut it as close to the main stem or trunk as possible instead of sending in just the branch tips or individual leaves.
If the disease involves wilting, or if Verticillium wilt or Dutch elm disease is suspected, bring several branch sections one inch in diameter and 12 inches long from branches with wilting or yellow leaves. Put samples in a plastic bag to prevent drying.
Turfgrass samples should be taken from the edges of affected areas. Collect one or two 3-by-3-inch squares of sod with an inch-deep section of attached roots and soil. Wrap each section in a slightly damp paper towel, then wrap it with newspaper and bring it in. Do not let the sample dry out.
When collecting fleshy specimens — such as fruit or potatoes — bring them with early and intermediate disease symptoms. Wrap specimens separately in dry towels or newspapers. Do not put it in plastic.
Finally, photos that show the entire affected plant would be very helpful too, especially for samples that are too big to send in an entire plant.
Just as when you go to the doctor, you will need to give some basic information, along with your diseased plant specimen, including:
- Where did the sample come from (your vegetable garden, lawn, greenhouse, etc.)?
- When did you first notice the disease?
- What is the plant's immediate environment (shade vs. sun; clay vs. loam; windy vs. protected, etc.)?
- How is the plant being cared for (overhead watering, drip irrigation, fertilizer, herbicides or pesticides, etc.)?
- What are the symptoms of the undiagnosed ailment?
Results are sent back to the local county office and an OSU Master Gardener™ volunteer or horticulture agent will call you with the results.
