Rust
Disease · Commonly affects: Beans, Asparagus, Garlic and onions, Sweet corn, Hollyhock, Snapdragon
Rust is a group of common fungal diseases, caused by fungi in the order Pucciniales, that infect the leaves, stems, and sometimes pods of many garden plants. Gardeners pay attention to it because heavy infections weaken plants, cut yields, and can spread quickly through a bed during warm, humid weather.
How to identify it
Look for small raised bumps or blister-like pustules, usually on the undersides of leaves, that break open to release powdery spores in shades of orange, rusty brown, yellow, or reddish. Rubbing an infected leaf often leaves a rust-colored smudge on your fingers, and matching pale yellow spots typically show on the upper leaf surface. As the infection ages, the pustules may darken toward brown or black.
Damage
Rust kills patches of leaf tissue, which reduces photosynthesis and makes leaves yellow, curl, dry out, and drop early. Severe or repeated infections stunt growth, lower fruit and vegetable yields, and can leave perennials weakened so they overwinter poorly.
Prevention
Rotate susceptible crops so the same plant family does not return to a bed for two to three years, and choose rust-resistant varieties whenever they are offered. Space and thin plants for good air movement, keep beds weeded, and grow plants in full sun with healthy, well-drained soil so foliage dries quickly after rain or dew. At the end of the season, clean up and remove old infected plant debris, since many rust fungi overwinter on leftover foliage and stems.
How to manage it
Pinch off and remove infected leaves as soon as the first pustules appear, and prune out badly affected stems to slow the spread. Water at the base of plants in the morning instead of overhead so leaves stay dry, and avoid handling or harvesting among wet plants because spores travel easily on moisture. Bag and throw away all infected tissue rather than composting it, and pull and destroy severely diseased plants to protect the rest of the garden.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.