I recently attended an in-service training led by a University of Tennessee Extension entomologist and plant pathologist to sharpen my skills in diagnosing ornamental plant diseases. It was a training I truly enjoyed. With the pop-up showers, high temperatures, and humidity we experience in July, plant diseases have been appearing in landscapes across Shelby County.

Diagnosing diseases in plants is much like being a detective. It can be challenging, but it is that challenge that makes it interesting. One thing I have learned over the years is that many plants have a few common diseases that develop when the right conditions converge. Plant pathologists call this the disease triangle. Disease occurs only when three things are present: a susceptible host plant, a disease-causing pathogen, and a favorable environment.

Correctly identifying the plant is the first step. Every plant species has its own group of common diseases. If the plant is misidentified, diagnosing the problem becomes much more difficult.

Next, examine the plant carefully. Which parts are affected? Are the leaves spotted or discolored? Are the stems, branches, flowers, or roots showing damage? Then, look for both signs and symptoms. A sign is the actual disease-causing organism you can see, such as fungal growth. A symptom is the plant’s response, such as wilting, yellowing, or leaf spots.

The next question is what caused the problem. Is it abiotic or biotic? Abiotic problems result from non-living factors such as drought, heat, poor drainage, or nutrient deficiencies. Biotic problems are caused by living organisms, including fungi, bacteria, viruses, or phytoplasmas. Determining the difference is often the most difficult part of the diagnosis.

Take the guesswork out of plant disease identification and obtain reliable information from Extension sources, such as UTHort.com, or contact your local Extension office. If you need help diagnosing a problem in your landscape, give me a call at 901-752-1207. I always enjoy playing plant detective!