The disease is caused by the fungus Botrytis cinerea.  This fungus is very common in most agricultural systems and causes disease on a wide range of crops.  The fungus grows well on dead and decaying plant tissue and can live indefinitely in the absence of a living host.  Cool moist conditions favor the growth of the fungus and in such environments, it can produce abundant airborne spores on a weekly basis.  The fungus can also produce hard irregularly shaped sclerotia which are long-lived resting structures.  However, not all strains produce sclerotia.

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