Botrytis (Gray Mold) Control
BOTRYTIS (GRAY MOLD) CONTROLGray mold rot (Botrytis blight) is a common fungal disease on plants, especially non-woody plants, grown under humid conditions. The fungus which causes the disease, Botrytis cinerea, attacks more than 80 kinds of plants in the Pacific Northwest. It is, however, serious on only a few of them.
HOST PLANTS: Common in tomatoes, cucumbers, green beans, as well as berries including strawberries, raspberries, and blueberries. It is sometimes a problem on ornamentals-particularly African Violets and other succulents.
SYMPTOMS: Botrytis blight affects plants in a number of ways. It may cause collapse and damping-off of seedlings, blossom blight, fruit rot, stem and crown rot, or shoot blight. The first symptom is usually a water-soaked spot. The tissue later becomes soft and watery. The affected parts of the plant wilt and collapse. If the humidity remains high, a grayish-brown coating or web of mycelium (fungus threads) and spores develops over the surface of the collapsed tissue.
Many spores are produced which are easily blown or splashed onto healthy foliage. If a film of moisture is present and other conditions are favorable, germination and infection can take place in a few hours.
Sclerotia may be produced on fleshy parts of stems and fruits. These are durable resting structures that permit the fungus to survive when conditions are not favorable for growth. They vary in size up to 1/4 inch and are flattened and black. Sclerotia are not always conspicuous, but may be embedded in decayed tissue or coated with soil and other debris.
FAVORED ENVIRONMENT: Gray mold overwinters on plants, in or on the soil, plant debris, and as sclerotia. Spores develop when conditions are optimal, and are moved by wind or splashing water onto blossoms or young leaves, where they germinate and enter the plant. Spores require cool temperatures (45-60 F.) and high humidity (93% and above) to germinate. Germinating spores rarely penetrate green, healthy tissue directly, but can enter through wounds on growing plants. Cuttings are particularly susceptible to infection.
BOTRYTIS (GREY MOLD) CONTROL: To avoid gray mold, increase spacing between plants and provide cross-ventilation. Prune or stake plants to improve air circulation. If growing indoors use a fan to improve air flow. Make sure to disinfect your pruning equipment (one part bleach to 4 parts water) after each cut. Keep the soil under plants clean and rake up any fallen debris. Add a layer of mulch after you have raked and cleaned the area well. Mulch will prevent the fungal spores from splashing back up onto the flowers and leaves. Water in the early morning hours (avoid getting water on the foliage) to give the plants time to dry out during the day. Make sure your soil mix is well draining.
Copper or sulfur based organic fungicides will help by protecting plants from infections. Apply these weekly, when spring weather is continuously cool and wet or if Botrytis has been a problem in the past. The biological fungicide Mycostop has shown suppression of the disease when applied directly to susceptible leaves, flowers and fruits.
Products for Botrytis (Gray Mold) Control