Sometimes It Takes an Expert

Coneflower with eriophyid mites. Photo by A. Windham

This purple coneflower with green ray flowers and distorted petals is infested with eriophyid mites.  It took a plant pathologist to determine that the casual diagnosis of aster yellows, a phytoplasma disease transmitted by leafhoppers, was not correct. Plants with aster yellows need to be removed to prevent disease spread. The plant shown with mites just needs to have the distorted flowers pruned away. Here is a photo of a plant with aster yellows​. Both images by A. Windham, courtesy UTIA. 

For many in Tennessee summer is defined by home gardens that are in full production and lawns that are well-cared for and lush. So, naturally, these enthusiasts want to be sure that the looming threats of plant diseases and pests are kept at bay.

University of Tennessee Extension plant pathologist Alan Windham says the best way to cure plant disease is correctly diagnosing the disease in the first place. “The best way to help struggling plants and landscapes is to have the problem diagnosed. Don’t guess. A correct diagnosis will help you make better decisions, cut your losses and allow you to plan for the future,” Windham says.

Where to start? Windham says plant pathologists begin by examining the entire plant. “A common mistake is to focus primarily on just the symptomatic tissue. It’s best to examine all the plant’s parts: the roots, stems and leaves.”
Experts also consider the weather. Wet weather is favorable for downy mildews, leaf spot, rusts or root rot diseases, while cool, humid weather is favorable for gray mold (Botrytis). Windham says hot, humid weather favors Rhizoctonia diseases and very hot weather favors southern blight.

Additional abiotic problems can make plants more susceptible to disease and pests. “Stresses like too little or too much water, heat or cold injury, pesticide injury and issues with pH and plant nutrition can all play a role in plant disease,” said Windham.  Many sorts of diseases can be expressed with symptoms like stunting, chlorosis, necrosis, leaf spots, leaf blight, cankers, rotted roots and soft rot.”

“At the UT Soil, Plant and Pest Center, we strive to get to the root of every problem,” says Windham. “Look for us at UT Institute of Agriculture field days throughout the year at our Diagnostic Tent, and at UT Extension continuing education seminars around the state.  We are happy to examine specimens that you bring to the events.”

Can’t make it to an event?  Send the Soil. Plant and Pest Center a specimen. To collect a proper specimen, when possible send the whole plant with soil or growing medium to the diagnostic lab. If the plant is too large, collect symptomatic leaves, stems and roots. Include a pint bag of the soil or growing medium. Ship or deliver the specimen to the lab as soon as possible before the sample deteriorates. Directions for packaging and shipping are on the SPPC website:

Windham and others regularly post information of interest to home owners and landscape managers on the website. For quick information and lively commentary on plant issues across the state, he invites everyone to follow SPPC on Facebook at:  

“We post great information about what’s bugging our clients,” says Windham.

Through its mission of research, teaching and extension, the University of Tennessee Institute of Agriculture touches lives and provides Real. Life. Solutions.



Alan Windham, Professor, Professor of Plant Pathology, UT Extension Soil, Plant and Pest Center,