White Rust

White pustules form on leaf undersides, sometimes with yellow zones on upper surfaces during cool, wet weather. This fungal disease requires alternate hosts to complete its life cycle. Remove infected material and avoid planting alternate hosts.

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.