There are several different leaf rust diseases of landscape trees and shrubs. Most of them require an alternate host during the life cycle. Part of the year, the infection is on the ornamental tree or shrub while the rest of the year it grows on another plant of a different species.

The spores of these fungal diseases are encouraged by warm, moist weather and spread between the hosts in the wind or by splashing water.

As the name implies, plants infested with a rust disease have some sort of "rusty" colored spots or growths (pustules) on their foliage. The leaves may also be mottled yellow or brown and twisted or distorted. Although it is often a chronic disease, plants may be stunted due to the loss of chlorophyll in the leaves. Some rust fungi produce spores in spots or patches, while others develop into hornlike structures.

The best way to prevent rust diseases is to grow resistant plants and keep them as stress free as possible. Rust disease in lawns is greatly encouraged by sites that are low in nutrients. For rusts that have alternate hosts, eliminating one of the two host species may help. Unfortunately, for the typical home garden, this is generally not effective.

Most rust disease of ornamental plants are primarily aesthetic and do not require treatment. However, several fungicides are labeled for use on these plants to prevent the infection. Removal of the alternate host from the area has been tried but is usually not effective.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Perhaps the most common of these diseases would include Cedar-Apple Rust.

 

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