Rust
A fungal disease that speckles leaf undersides with raised orange, brown or rusty pustules.
🔍 How to spot it
Small raised pustules of orange, yellow, brown or reddish spores, usually on the undersides of leaves, with matching pale or yellow spots on top. Rub one and the powdery, rust-coloured spores smudge your finger. Heavily infected leaves yellow and fall.
💥 The damage it does
Rust drains the leaf and blocks light, weakening the plant and causing early leaf drop, though it rarely kills established plants outright. It spreads on the wind and on splashed water, and can build up year to year on the same plants outdoors.
🧴 How to treat it
Pick off and bin infected leaves at the first sign, and never compost them. Improve airflow and keep the foliage dry. Sulphur or other rust fungicides help on valued plants, but good hygiene and removing infected growth are the mainstay.
🛡️ How to prevent it
Space plants well, water at the base, and clear fallen leaves that harbour spores over winter. Grow resistant varieties where rust is a known problem, and avoid wetting the leaves.
🌿 Plants that get rust
A garden disease of roses, alliums, hollyhocks and many perennials. These 46 profiled plants name it in their own troubleshooting notes:
Houseplants 3
Garden 34
Struggling to save a plant? The plant rescue guides walk through recovery step by step, and the problem solver works backwards from a symptom. This is general growing advice, not a diagnosis for a specific plant.