The days are getting shorter, a chill is in the air but the drought is still holding. Environmental conditions are often predisposers of disease and while typically dry conditions suggest less fungal disease, this is not always the case in nurseries. Cooling weather is a time to be watchful for diseases caused by Botrytis. Botrytis cinerea, the asexual stage of Botryotinia fuckeliana,is a necrotrophic fungus that uses enzymes to dissolve host tissues and then absorb the remains. This fungus thrives in cold and wet conditions and will rapidly invade wounded or frost-injured plants. Herbaceous plants or flowers of woody plants (Rose) are particularly susceptible to Botrytis rots.
These are quickly diagnosed because the mycelium is easily seen growing on affected plants as “gray mold” which gives it the same common name (fig. 1). Actually the gray part is comprised of spores (conidia) that occur in bunch-like clusters. (Botrytis is Neo-Latin and originated from the Greek botrus for “bunch of grapes.”) Botrytis rot affects over 200 crop hosts and likely more plants that have not been studied. While various classes of fungicides are available for control, the pathogen is genetically pliable and easily resists typical fungicide regimes. Since the pathogen reproduces rapidly by asexual spores (conidia) it is important to rogue affected plants or trim and dispose of affected parts. Increased spacing to prevent plant-to- plant contact will also slow spread of gray mold. For more information on gray mold see: http://www.ipm.ucdavis.edu/PMG/r280100511.html.
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