We’ve all forgotten a carton of strawberries in the crisper drawer of our refrigerators and returned to find it covered in a fluffy gray mold. As disappointing as it is for consumers to throw them in the trash, growers are constantly battling the Botrytis cinerea pathogen from the time their plants enter the ground until they’re harvested and sent to the market.
Mengjun Hu, associate professor in the Department of Plant Science and Landscape Architecture, is on the frontlines of this microbial battle, conducting research into the response and resistance of gray mold to common fungicides. His work will help producers control the disease and improve yield, not only for strawberries, but for all small fruits, vegetables, and ornamental flowers that are affected by gray mold.
“Gray mold has a wide range of hosts and it’s one of the few strawberry diseases that drives the need for frequent fungicide applications,” Hu said. “It primarily causes infections on the fruit so it directly affects yield as well as quality.”
To manage gray mold, farmers have typically used a calendar-based spray program, involving a variety of single-site fungicides, which attack a single metabolic site in the fungus and prevent it from growing. But Hu’s research is showing that Botrytis quickly develops a resistance to these fungicides after frequent use.
“For extreme cases like Botrytis, which has a tremendous ability to show resistance to multiple chemical classes of single-site fungicides, we need to think about our general resistance management strategies,” Hu said.
The General Resistance Management Strategy is to rotate or mix different single-site fungicides. “Unfortunately, this recommendation is unsustainable as more single-site fungicides are involved in a spray program, the faster Botrytis strains with multi-fungicide resistance will be selected.” The alternative, Hu suggests, is to base resistance management on the use of multisite fungicides—which effectively attack multiple metabolic sites.
Although many IPM (Integrated Pest Management) programs favor single-site fungicides because of their toxicity profiles, multisite fungicides are preferred for controlling gray mold because the pathogen is unable to develop a resistance to that class, Hu explains.
Multisite fungicides should be the backbone of a grower’s spray program, he said, with single-site fungicides only being applied when infection risk is imminent. And even then, they should be tank-mixed with the multisite fungicide.
Dry weather conditions are the best deterrent of gray mold in the field, and more effective than any class of fungicide, Hu said. Producers can use tools that provide real-time weather conditions to predict infection risk and spray according to these models, said Hu, saving them unnecessary applications and thus, time and money.
“The key to resistance management, in my opinion, is minimizing unnecessary sprays with single-site fungicides,” said Hu. “In this case, less is more.”
by Laura Wormuth