Grey Mold

Widespread and very contagious fungal disease Botrytis cinerea

Grey mold is a fungal disease, caused by fungus Botrytis cinerea. It's spores are around us (in atmosphere, soil and water) all of the time, and it lives on both living and dead plant material.
Botrytis at first appears as a white growth on the plants, but very soon changes to a grayish-white, and next to dark gray. These gray spores form and are spread by the wind or in water. In greenhouses and tunnels any activity will result in a release of spores. Even automated trickle irrigation systems, when turned on, trigger a release of spores. These spores are often found on the outside of seeds. The spores can remain dormant on plant surfaces as long as the life of the plant in some cases. Botrytis forms two types of resting structures on or in infected plant tissue: 1) very dark brown or black multi-celled structures called sclerotia and 2) single-celled, thick, dark walled chlamydospores.
During the winter numerous small, raised, black sclerotia (resting bodies) may be seen on plant debris. These are around 3-5 mm long and are capable of surviving long periods of harsh weather. They remain dormant until conditions are favorable. Early in the summer, grey mold enters the flowers as they fade and remains dormant in the fruits until they begin to ripen, when the grey, fuzzy, spore-producing structures develop. Grey mold can also colonise the straw that is used to mulch strawberries.
  1. Sanitation is the main. Remove dead or dying stems, canes and leaves from the plants and from the ground. Remove this refuse from the greenhouse and tunnels. Do not throw debris under benches or on walks. Sanitation alone is not sufficient to control this fungus.
  2. Avoid injuring plants in any way. Do not leave large stubs of tissue on stock plants when taking cuttings.
  3. Heat and ventilate greenhouses and tunnels to prevent high humidity conditions. This may only require extra venting early in the day when moisture has condensed and before sunlight has warmed the air. Even lowering the humidity slightly can have a significant effect on Botrytis. Outdoor planting should be planned to provide good air circulation patterns.
  4. Added protection is available for many crops by applying a fungicide or biological control agent. Note that some Botrytis populations are resistant to certain chemicals. This becomes a problem when those fungicides are used exclusively over a long period of time.
Use Elevate, Pristine, Switch, Rovral, Ronilan or Thiophanate-Methyl, other liquid copper or organic (bacterial) fungicides to reduce the probability of infection. Avoid excessive nitrogen fertilizer applications. Pick fruit frequently.