Symptoms: Found on a wide range of plants (too many to mention), gray mold (Botrytis cinerea) is a fungal disease that travels quickly through gardens, especially during damp, cool to mild weather. It can be identified as grayish colored soft, mushy spots on leaves, stems, flowers and on produce. Spots may become covered with a coating of gray fungus spores, especially if humidity is high. Fruit or plants shrivel and rot and often develop black, stone-like sclerotia under rotted parts.
Gray mold is often found near the soil surface or in the densest areas of the plant canopy. It develops on wilted flowers first, then spreads quickly to other parts of the plant. The disease may also occur in storage, causing rotting of harvested fruits and vegetables.
Gray mold overwinters on plants, in or on the soil, 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.
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.
Photo Credit: Daily Mail, U.K.