by Dr. Stephen Nameth
Department of Plant Pathology
Without a doubt the most common disease of greenhouse floral crops is gray mold. The disease can affect almost every type or variety of floral crop grown. This disease can either be a common nuisance or an economic disaster depending on the host and the conditions under which the crop is grown. It is also one of the easiest diseases to control using nonchemical means.
SYMPTOMS
Symptoms of gray mold vary depending on the host and the environmental conditions associated with the host. Under most conditions and with most hosts the disease is characterized by the production of leaf spots, flower blight, bud rot, stem canker, stem and crown rot, cutting rot, damping off, and in extreme cases, plant death. When conditions of high relative humidity prevail, at or above 85%, the fungus can be seedn growing and sporulating on the infected tissue. Fungal growth is characterized by the presence of fluffy, gray/brown mycelium that produces a cloud of spores if disturbed. Affected tissue is soft and brown, and sometimes has a water-soaked appearance.
CAUSAL AGENT AND DISEASE CYCLE
Gray mold is caused by the fungus Botrytis cinerea. It is a common fungus, with a very wide host range and can persist in the greenhouse year-round as mycelium, conidia, or as sclerotia on living or dead tissue. The fungus produces a large amount of spores that move throughout the greenhouse via air currents. Under optimum environmental conditions (relative humidity at or above 85%, with little or no air circulation or with free water on the leaf surface), the spores land on the plant surface, germiante, and penetrate the host plant.
DISEASE MANAGEMENT - Control the Environment
If there is one practice that will go a long way toward the management of gray mold, it is controlling the environment. Maintaining an environment within the greenhouse that will not permit the fungus to grow and sporulate is essential to control. By keeping the relative humidity below 85%, as well as maintaining good air circulation and adequate plant spacing, excellent control can be achieved. Whenever possible, plants packed closely together should be spread apart to allow better air circulation and to reduce relative humidity within the plant canopy. Fans should be used to provide good air movement above the canopy. Plants with wounds should be either protected with a fungicide or removed from the greenhouse, as the would is the perfect environment for the fungus to initiate the infection process.
SANITATION
Infected plant material should be removed from the greenhouse so that it is not a source of inoculum for the rest of the house. Infected plant material should not be allowed to sit in trash cans within the house as the fungus will continue to grow and sporulate on the dead and dying tissue. Subsequent opening and closing of the trash cans will produce enough air movement to release spores out into the greenhouse.
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