Disease guide

Botrytis cinerea (teleomorph: Botryotinia fuckeliana)

This fungus can infect all above ground parts of the plant and typically enters through wounds. On the stem, initial infection appears as elliptical, water-soaked lesions. These lesions develop under high humidity into a gray, moldy growth, which can girdle and kill the plant. Stem lesions often show concentric banding. Leaf infection usually begins at a point of injury and develops into a V-shaped lesion, which is covered with gray fungal sporulation. This fungus commonly infects the calyx end of the fruit where it can spread rapidly, forming gray-brown sporulating lesions that later develop into a watery rot. Ghost spot, an unusual fruit symptom often observed, is characterized by small white to pale yellow or green rings developing on green or red fruit. These result when the fungus infects the fruit but further disease development is halted when the fruit is exposure to direct sunlight and high temperatures. Ghost spot does not develop further, but spots reduce market quality.

This fungus has a wide host range, is an efficient saprophyte and can survive in the soil and infected plant debris for long periods in the form of sclerotia. It is considered a weak parasite and typically infects the plant tissues through wounds. When humidity is adequate, gray masses of fungal spores are produced and readily wind disseminated. Overcast, cool and humid conditions are required for disease development. Close spacing and poor ventilation can lead to severe gray mold problems.

A good fungicide spray program and providing adequate ventilation to the plants by pruning and subsequently applying a fungicide to the pruning wounds can help reduce losses from this disease.