The premature leaf fall adversely affects fruit quality and flower development.
Rust (prune and plum) [Tranzschelia pruni-spinosae]
Initial occurrence in mid-July. The fungus reproduces through brown summer spores formed on the undersides of the leaves. Although plum rust only livers of live plant material unless it produces resting spores it therefore lives on other host plants when the plum trees are dormant.
Pattern of damage
Small yellow spots on the upper sides of the leaves; (Picture 1) initially brown, eventually black pustules on the undersides of the leaves (Picture 2). Severely infected leaves turn brown and are shed.