Rust

Rust begins on the undersides of leaves as powdery pimples, usually orange yellow in color, though it may occur in many other colors. These pimples are made up of millions of microscopic spores. The spores are released during cool moist conditions and travel by wind and water. As the rust develops it will cause the top side of the leaf to have yellow spots and eventually the entire leaf will turn yellow. Rust can kill a plant if not controlled.

Pathogen:
There are thousands of types of rust and most are species specific, attacking only one type of plant. Carefully inspect plants before purchasing them and keep you garden tools clean.

Environment:
Rusts get busy during cool moist conditions. Provide good air circulation by properly spacing plants to reduce moisture and above all do not water in the evenings. Also, avoid overhead watering and do not work in beds while the plants are wet.

Hosts:
Rusts attack many types of plants. The images on this page are of rust on Beebalm (Monarda didyma.) Apples, crabapples, roses, and snapdragons frequently develop rusts as well, which has spurred the introduction of rust resistant varieties.

Management:
Remove and destroy all infected parts of plants. Do not add to compost. Because rusts will infect many, many types of plants it is best to look for a fungicide aimed at rusts for that plant. Check the labels for plant listings. Common fungicides are Daconil, mancozeb, and Immunox. Apply fungicides according to label directions.

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| Controlling Existing Pathogenic Diseases |