Accurate diagnosis of a plant disease depends on having a fresh sample representative of the problem. To get an accurate diagnosis when your plant has a disease problem, you need to collect the right kind of sample.
You also need to provide complete information about the plant and its history. Since the county Extension agent and the person making a diagnosis probably won't see the problem first hand at the growing site, you need to help them create a mental picture of the disease situation. You can provide this help by filling out the information requested on various Plant Disease Diagnostic Lab forms, along with the sample. Complete information and a representative sample are keys to an accurate diagnosis.
Before you collect the sample, please find the part of this publication relating to your plant's problem and read it carefully. Doing so can save you a lot of wasted time and effort and will help you get an accurate diagnosis.
Eshenaur, B. C.; Bachi, Paul R.; Nesmith, William C.; Hartman, John R.; Hershman, Donald E.; Vincelli, Paul C.; and Kaiser, Cheryl A., "Submitting Plant Specimens for Disease Diagnosis" (1990). Agriculture and Natural Resources Publications. 49.