Rust
Puccinia spp., Uromyces spp., Phragmidium spp., Gymnosporangium spp., Tranzschelia spp.
Overview
A large group of fungal diseases characterized by orange, yellow, brown, or reddish pustules on leaves and stems. Rust fungi are obligate parasites that require living plant tissue to survive.
Symptoms
Orange, yellow, brown, or reddish-brown pustules (uredinia) on leaf undersides and stems. Upper leaf surfaces may show yellow spots corresponding to pustules below. Severe infections cause defoliation and weakened plants.
Environmental Conditions
Humid
Prevention
Plant resistant varieties. Remove alternate hosts where applicable. Ensure good air circulation. Avoid overhead watering. Remove and destroy infected plant debris in fall.
Management
Apply sulfur or copper-based fungicides preventively. Remove infected leaves promptly. Neem oil can slow spread. For cedar-apple rust, remove galls from junipers within a mile radius.