Leaf Rust

Rusty-orange or brown pustules form on leaf undersides by late summer and fall, causing yellowing and early leaf drop that weakens plants. Rust overwinters on alternate hosts and spreads readily by wind-dispersed spores. Remove severely affected foliage and destroy it immediately. Avoid planting susceptible species in close proximity to alternate hosts that can harbor the fungus.

Rust fungi often need two different host plants to complete their life cycle, so identifying and managing the alternate host can break the cycle. Remove heavily infected leaves and dispose of them away from the garden. Improve air circulation to speed leaf drying after rain. Fungicide applications are most effective as preventive treatments before symptoms appear; once pustules are visible, the current infection cycle is already underway.