Cedar Apple Rust


Rust is a common fungal disease of many different edible and ornamental plants. The bright red, orange, yellow or brown colors of this disease draw attention to and can detract from the plant’s appearance. In severe cases, leaves may completely turn yellow and fall off the plant. On plants such as herbs where the foliage is eaten, the disease may compromise the use of the plant.

Each different species of rust fungi is only able to infect a limited group of plants. Some infect only one species of plant, while others are able to infect several different plants. Some rust fungi species spend half of their life on one group of plants and the other half on a completely different plant. A common example is cedar apple rust, which spends half of its life infecting junipers and the other half infecting apple or crabapple trees. Choosing rust resistant plant varieties can help to prevent the disease.

No matter the species, the fungi that cause rust disease need water on the surface of the leaves to start growing. Reduce moisture on plant leaves. Avoid overhead watering and water at the base of the plant instead. Pinch off rust infected leaves when first seen and destroy them. Inspect plants more during periods when humidity and moisture levels are high. Provide adequate spacing between plants to improve air circulation. Fungicides must be applied to healthy green plant tissue early in the growing season before infection begins. Repeat applications may be required, especially when conditions are conducive to the development of the disease.