Botrytis cinerea occurs abundantly throughout the year as a saprophyte and facultative parasite on a wide variety of plant materials in raspberry and strawberry plantations. Despite high concentrations of airborne spores at the time of fruit development, relatively few infections have resulted from penetration of fruit surfaces following the germination of spores in drops or films of water, uninfluenced by the presence of necrotic tissues. The majority of fruit infections are initiated from mycelium growing saprophytically in contiguous plant material or from spores germinating in solutions trapped between such material and the fruit surface.
Dry spores of B. cinerea on the surface of strawberry fruits do not readily germinate in a saturated atmosphere but germinate rapidly in a water film. Although ripe and unripe fruits differ markedly in susceptibility, fruit maturity induces only small differences in the rates of spore germination. Field observations suggest that water films generally do not persist on the surface of the fruit long enough for the post germination infection process to be completed. Such films, however, may persist much longer when trapped between floral parts, and spores germinating there are able initiate infections almost as soon as the buds open. The process may be accelerated by the presence of necrotic tissue, for example, in flowers damaged by frost. Mycelium infecting floral parts may subsequently invade the proximal end of both strawberry raspberry receptacles. This mycelium may remain quiescent until the fruit ripens; subsequently infected fruit may escape notice during picking and marketing.
Some methods of supplementing fungicidal control measures by reducing the incidence of sources of infection are suggested.