Botrytis Blight on Orchid

Description

• Botrytis blight, also called gray mold, can strike any part of an orchid plant but usually attacks spent flowers. A fungal disease, botrytis grows best when the climate is cool and humidity is high. The fungus moves on the wind or splashing water and waits until the climate conditions become suitable for its spores to germinate. The spores can lurk in the soil and may enter healthy plants through wounds.

Symptoms

• The first sign of trouble is necrotic brown to black spots on wilted flowers. The spots start out small and may have a pinkish cast or a pink margin. Spots sometimes show up on the plant's oldest leaves, as well, and may distort the leaves. When humidity is 85 percent or higher for an extended period, the spores multiply and become visible on the infected areas. The spores resemble gray dust and, like dust, rise in a cloud when disturbed. As the disease spreads, so do the spots, becoming larger and more numerous. In addition to the gray, moldy-looking patches, cankers or lesions may form on the stems, causing tissue collapse and rotten stems.

Control

• Botrytis is not curable. Since the spots generally appear on spent flowers, remove dead flowers and leaves and dispose of them far away from the orchids. Orchids generally recover quickly from botrytis and new growth comes in disease-free. Remove severely infected plants and dispose of them and the growing medium. Disinfect the container and use fresh, sterile growing medium for new orchid plants.

Prevention

• Remove all plant debris from fallen leaves or flowers that land in the pot. If the orchid is in the garden, make sure no weeds are growing nearby. Indoors or out, make sure the orchid has good air circulation to help keep the leaves dry after rainfall or watering. Do not use overhead watering unless you do so early in the day so the leaves and flowers have time to dry. Check the garden or container for proper drainage. If water stands too long around the orchid after watering, cut back on watering and provide better drainage. Reduce humidity levels to below 85 percent, especially during cool weather. If the orchid has companion plants in the container, inspect those for signs of botrytis infection and get rid of any that may be spreading infection to the orchid. Keep infected orchids away from healthy ones or remove and destroy diseased plants altogether. Use a fungicide on orchids in the garden to help prevent infection and follow label instructions carefully.