HORTICULTURE

Detailed explanation-1: -Biology. The fungus produces spores in the black spot lesions on the upper leaf surface and these spread in water to initiate new infections. Wet conditions are required for the disease to build up, but most summers in the UK are sufficiently wet.

Detailed explanation-2: -The disease is caused by the fungal pathogen Diplocarpon rosae. Leaves are most susceptible when young and must remain moist overnight before infection can occur. The disease can be spread by rain, dew, irrigation, people, insects, and transport of infected plants.

Detailed explanation-3: -Black spot may develop in fruit when they begin to ripen and in leaves when conditions favour disease development. The main source of infection is spore masses produced on old, undecomposed leaves and shrivelled fruit. The spores are spread by rain splash, by overhead irrigation and on the hands of pickers.