Kentucky growers, both of vegetables and tobacco, should be on the lookout for Botrytis gray mold. This disease may occur in the field under humid conditions, but is most common in greenhouses or high tunnels. Botrytis gray mold can also affect numerous other herbaceous plants, including ornamentals. Prevention, early identification, and management will help reduce plant losses.
Here are the symptoms to look for, preventative tactics, and brief suggestions on how to treat crops once disease is confirmed.
Cause and Disease Development
Botrytis gray mold is caused by the fungal pathogen Botrytis cinerea. The pathogen overwinters in plant debris from the previous season or in soil. Botrytis spores are easily moved by wind, air currents, or water. All above-ground plant parts may become infected at any stage throughout the growing season, which can result in blighting, or fruit or plant loss. Botrytis gray mold is favored by high humidity. Once established the disease can spread rapidly in dense plantings.
Transplants may become infected prior to setting in the greenhouse or field. Wounded plant tissue is especially susceptible to Botrytis infection. Tan-brown lesions with an abundance of gray spores develop on leaves, stems, hanging blossoms, tobacco clippings, or fallen fruit (Figure 1). Stem lesions may expand to cause girdling, resulting in wilting or plant death. In tobacco, Botrytis may expand to the leaf veins, resulting in a darkened color and dying areas along the clipping wound. Infected fruit develop a grayish, soft rot, and the skin becomes discolored and cracked (Figure 2) with masses of gray, velvety spores. Occasionally, green fruit develop “ghost spots” that make fruit less desirable.
- Remove plant debris, tobacco clippings, or weeds from the growing area.
- Remove and destroy heavily infected plants or plant parts.
- Mow, prune, clip, or trellis plants only when they are completely dry to minimize plant injury.
- Avoid overhead watering to reduce leaf wetness.
- Improve greenhouse ventilation to reduce humidity.
- Use recommended plant spacing to facilitate air movement and leaf drying.
Start plants on a preventative fungicide program within 3 weeks of transplanting.
- Greenhouses: Mancozeb, copper, and Botran are good early-season options. If gray mold has already begun to affect over 5% of the crop or first harvest is approaching, see ID-36, page 18 for 8 different chemical options with shorter preharvest intervals.
- Field: Early season programs focusing on mancozeb, chlorothalonil, and copper should prevent initial infections. A number of effective chemical options exist for application later in the season (see ID-36, page 97 for sample program).
- Greenhouses: Both mancozeb and the single labeled Quadris application for target spot management should help manage gray mold.
- Field: Gray mold is rarely a problem in field plantings because of reduced humidity and improved plant spacing present in fields.
As always, all label recommendations must be followed when applying fungicides to crops. Pay close attention to pre-harvest intervals as well as tobacco contract obligations in the application of any fungicide.
- Botrytis Gray Mold of Tomato, Vegetable Pathology Fact Sheets, NC State University Cooperative Extension (link)
- The Effects of Variety, Harvest Management, and Curing Environment On Cured Leaf Quality of Burley Tobacco (AGRONOMY FACT SHEET TOB-1-09)
- Greenhouse Sanitation (PPFS-GH-4)
- Home Vegetable Gardening (ID-128)
- IPM Scouting Guide for Common Pests of Solanaceous Crops in Kentucky (ID-172)
- Managing Greenhouse & High Tunnel Environments to Reduce Plant Diseases (PPFS-GH-1)
- Mold on Curing Tobacco (PLANT & SOIL SCIENCES FACT SHEET TOB-2-05)
- Vegetable Production Guide for Commercial Growers (ID-36)
- IPM Scouting Guide for Common Problems of High Tunnel and Greenhouse Vegetable Crops in Kentucky (ID-235)
Kim Leonberger, Extension Associate and Emily Pfeufer, Extension Plant Pathologist