Recent cold weather across South Carolina may lead to problems with white mold on winter vegetables, Clemson University experts say.
White mold, also known as Sclerotinia, is a fungus that infects more than 350 species of plants, including collard, kale, cabbage, broccoli, parsley, carrot, lettuce and potato. Mold symptoms appear on blossoms, stems, leaves and pods. Typically, white mold infects plants during the winter, spring or summer. It may not be noticed as it develops. White mold fungus releases spores when the weather is cool. These spores can be carried by the wind and infect other plants.
Scouting is important said Anthony “Tony” Keinath, Clemson vegetable pathologist at the Clemson Coastal Research and Education Center. When scouting for white mold, it is important to check the stems as water-soaked stems, or parts of stems, may be the first symptom growers detect.
“Other symptoms include a white dense cottony growth on stems, leaf stems, fruit and plant crowns,” Keinath said. “Other symptoms include discolored lesions on areas near the crown (top) of the plant.”
Plant injury, either by freezing or mechanical damage, makes easy entries for white mold to infect plants. Both cold-damaged tissue and diseased tissue may be straw-colored or bleached.
Once plants become infected, white mold is difficult to control, said Powell Smith, Clemson Extension entomologist in Lexington County.
“The fungus that creates white mold can survive in the soil for years,” Smith said. “Once a plant is infected, white mold cannot be stopped.”
Spring crops could be in danger as well. Wind can blow spores from the fungus and infect additional fields or gardens.
If white mold is found, it can be controlled by:
- Increasing in-row spacing between plants to allow the plants and soil to dry faster;
- Eliminating weeds that are hosts, such as Carolina geranium, chickweed and henbit;
- Scheduling irrigation in the morning so that the plants and soil dry quickly; and
- Rotating infested fields to non-host crops in the grass family.
According to Keinath, fungicides in FRAC Group 7 cannot be rotated with each other. Rovral cannot be used on leafy brassica greens. Organic growers can use the biofungicide Contans. This biofungicide works better when applied a few weeks before the sclerotia germinate.
For more information about which plants can be sprayed with the fungicides listed in the table above, see the 2018 Southeastern U.S. Vegetable Crop Handbook. Download the white mold factsheet: White Mold 2018.