Rust Disease in Garden Plants
Rust disease comes in many forms. It can be bright orange, reddish, yellow or brown, and it can show up as flat or raised spots on a plant. It is commonly found on the underside of a plant's leaves but can be found on other plant parts, such as the stems, flowers and fruit. Serious rust disease may cause stunted growth or the plant may die. Rust disease on flowers cannot be spread to vegetable plants, and vice versa.
Rust is a fungal disease that affects trees, vegetables, grasses and flowers. The disease weakens a plant by reducing the amount of food it takes in from the roots and the leaves. Wind and splashing water spread rust spores, and the spores develop quickly in wet or humid weather. Spores that spread rust disease live on plant debris during the winter and attack new plants during the summer. Rust disease grows rapidly in temperatures of 50 to 75 degrees F.
Spots created by rust disease are light orange, red, yellow or brown in the early stages of the disease, and they turn a darker color as the disease progresses. The leaves of a plant may begin to fall off as rust disease advances. The disease causes swelling or canker spots on the trunk of some plants.
Rust disease infects birch, pine, cypress and spruce trees. The main flowering plants that the disease attacks are roses, snap dragons, day lilies, gardenias and carnations. The main vegetables affected by rust disease are tomatoes, asparagus and beans. In vegetable and flowering plants, this disease causes the flowers and fruit to become deformed or a severe reduction in the amount of fruit or flowers produced. Kentucky bluegrass and perennial rye grass are grasses most frequently affected.
To prevent rust disease, keep plants spaced and pruned to provide good air circulation. Avoid overhead watering and do not work around a wet plant, as this can cause rust spores to spread. Always remove and destroy infected debris as well as severely infected plants to prevent spread of the disease. Keep weeds away from the plants, as weeds help promote growth of the disease. Thoroughly clean any garden tools that have been used on infected plants before using them on healthy plants.
All types of rust disease are different so there is no one treatment that cures all forms of the disease. One method to try is sprinkling sulfur on the plants and around the garden area. If organic treatments are preferred, Neem oil and a fungicidal soap are safe for almost all plants and animals. Plants should be treated weekly for one month to avoid recurring infections. If chemical treatments are used to rid plants of rust disease, purchase fungal sprays such as Funginex or Triforine and follow directions on the bottle.
- University of California IPM Program: Managing Pests in Gardens
- University of Rhode Island Greenshare: Some Common Fungal Diseases of Turf
- “Insect, Disease and Weed I.D. Guide”; Anna Carr, Linda Gilkeson and Miranda Smith; 2001
- “Ortho’s Home Gardener’s Problem Solver”; Meredith Books; 2001