The fungus overwinters on fallen leaves in the form of fruiting bodies, which can withstand severe winter conditions. The following spring these structures produce spores of a different type from those formed on the plant in the summer. These spring spores attack the young leaves to start the infections for that season. Once the disease is present on the bush, it is spread further by the rain-splashed summer spores produced on the leaf spots.
Leaf spot is usually most severe on weak bushes, and the premature leaf fall reduces their vigour still further. The disease is also often troublesome on bushes growing on light soils.