Grey Mould, Botrytis cinerea
Botrytis cinerea is a fakultative parasite, because it grows on dead plant material too. Because of this fact it is always present in vineyards, orchards and permanent land. Botrytis cinerea is related to moist climate. Infection takes place at very high relative humdity or the presence of free water. The fungus is unable to infect healthy adult plant material by spores. Infection takes place on young shoots during longer wet periods or an shoots damaged by hail storms.
Botrytis cinerea infection is favoured by leaf wetness. For the infection of detached berries the relation between leaf wetness duration and temperature leading to infection is shown in the graph above. This findings coming out a study perfomed at the UC-Davis. Pessl Instruments is using this relation as the basis for our B. cinerea risk model. Increase of risk is proportional to this graph and three completed infection periods would lead to a risk of 100%. Any leaf wetness period will lead to an increasee of risk which is proportional to this. Days with less than 4 hours of leafwetness will lead to a reduction of the risk by one fifth of the actul value.