Prevent a plant plague: UW Extension offers disease diagnosis

Black-thumbed gardeners now have access to the plant doctor through the University of Wyoming. 

Jean Williams-Woodward, plant pathologist at the University of Wyoming, taught local gardeners how to identify and prevent plant diseases at the UW Extension Garden Expo in Basin last month. 

“I can tell you how all of your plants will die, and I get happy about that,” Williams-Woodward said to a chorus of laughter. 

The death knell for plants comes in a trifecta: The Plant Disease Triangle. For disease to persist, it needs a host capable of becoming infected (pretty much every plant), pathogen (usually host-specific) and a beneficial environment.

“Where you get disease is actually where all of these overlap and come together at the same time. The way we try to manage diseases is removing one part of the triangle,” Williams-Woodward said. 

“Every plant has at least one plant pathogen that affects it.” 

Over time, some plants have been developed to be genetically resistant to common diseases. Cucumbers and squash, for example, are susceptible to powder mildews. Now, you can buy disease-resistant plants and seeds to avoid that. 

However, if you’re fond of your heirloom tomatoes, you may also protect them by controlling the other two factors: pathogen and environment.

When buying plants from a greenhouse, Williams-Woodward suggested pulling them from their container to check the roots. 

“When you’re buying a plant, you’re buying a root system,” she said. 

Plant diseases are roughly 80% fungus, 10% bacteria, 7 % viruses and 3% nematodes, microscopic roundworms. Fungus can stay in the soil even after a plant dies, and viruses may be passed via insect vectors or through seeds. Prevent bringing new diseases to your garden when possible.

Look for root rot, and also check the leaves for fungal spots, powder mildew, and white mold on stems. 

If you do end up with disease in your garden, try not to pass it on to the next generation: do not collect seeds from a diseased plant. In the case of viral diseases, like beet curly top virus, Williams-Woodward said to kill the plant before the plant kills your garden. 

“The only thing you can do is get rid of it, get rid of the affected plant,” she said. 

Rotate your crops so that left-behind plant pieces from last year don’t spread disease to new hosts. By changing plant families in a location, it becomes less likely the new crop we be susceptible to the same disease. 

Watering is important in controlling environment. Stressed plants are more susceptible to pathogens. Watering the ground directly and keeping water off of leaves when possible also gives disease less opportunity to spread. 

“A lot of our irrigation practices here in Wyoming have changed, so now we’re seeing a lot of pivot irrigation going in, which actually means you’re wetting the leaves, which actually means you’re going to get more diseased crops,” Williams-Woodward said. 

Air flow also helps plants avoid illness; Williams-Woodward suggested keeping space between plants and trellising vining plants. 

The most important thing to keep your garden healthy is to prevent disease buildup, Williams-Woodward said. 

“The first year, nothing’s there… by the third year, if you don’t do something about it, you will have a lot of disease,” she said. 

If worse comes to worst, the University of Wyoming has a diagnostic lab. Start with the local Extension Office at 208 S. Fifth St. in Basin, or visit the plant clinic online at https://wyoextension.org/plantclinic.