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How to Detect and Prevent Rust in Plants. Rust is a fungus characterized by orange-brown, powdery blisters or pimples found mostly on the undersides of leaves and stems, resembling the rust that you find on metal. Roses are susceptible to this fungal disease, and once infested are difficult - but not impossible - to cure.
Look for rust on the undersides of foliage. It's orange in color and has a velvet appearance.
Remove any infected leaves immediately and discard.
Rake up and destroy all fallen leaves and debris. Do not compost.
Avoid overhead irrigation. Rust spores are carried back up to the plant by splashing water. Apply water at the base of the plant to avoid splash back.
Protect plants from high humidity and heavy rainfall. Place susceptible plants under overhangs or eaves to prevent wetting the foliage.
Water in the early morning hours so the plant has a chance to dry during the day.
Clean tools used to prune infected plants with a 1-to-1 bleach/water solution to prevent spread of disease to other plants.
Spray plants with sulfur-based fungicides. After dormant-season pruning, spray with a lime/sulfur spray or a Bordeaux mixture to kill overwintering fungus spores.
Roses, hollyhocks and snapdragons are most commonly affected by rust. Keeping the area under the plant clean increases your chances of successfully combating this fungal disease. Always use the least toxic method of pest control as your first step.
Fungicides are among the most toxic chemicals used in the garden. Always wear protective clothing including neoprene gloves, a respirator, long sleeves and pants, and goggles when applying fungicides.