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Past Articles Library | Plant Diseases & Control | Rust

Rust is a widespread fungus that can affect many hosts. Dry rusty red, orange yellow, or whitish spots (spore masses) show up on leaves and stems, and occasionally on flowers or fruit. Look for rust on underside of leaves, the upper surface of heavily infested leaves turn yellow or brown, and may drop prematurely. Heavy infestations may cause galls on leaves or stems.

Rust fungi infect under mild, moist conditions. Many species also form black overwintering spores on leaves in the autumn, which start the disease cycle in the spring. Most infections stay local but spores are spread by wind, sometimes for hundreds of miles, and come down in rainfall to start new infections.

Many hosts including: birch, cottonwood, cypress, false cypress, fuchsia, hawthorn, juniper, pine, poplar, rhododendron, rose, spruce, snapdragon, asparagus, carnation, and raspberry.

Some infestations are severe enough to cause branch dieback and occasionally kill the entire plant. Some rusts may cause leaves and shoots to become distorted, dwarfed, and discolored.

Organic Control: Avoid overhead watering and do not work among plants while leaves are still wet. Grow resistant cultivars. Provide good air circulation to permit foliage to dry quickly. Destroy infected leaves to slow the spread of disease and spray or dust weekly with sulfur. Chemical Control: Spray with Funginex or Triforine.