Roses with Orange Spots

Asked April 30, 2019, 5:41 PM EDT

I found my roses today with orange spots. The back side is bumpy. What might they be and how might I cure the plants?

Multnomah County Oregon

1 Response

Thank you for the excellent images of rust on your rose. Rust is one of the rather common leaf diseases of roses in our mild, humid, rainy climate. Then, too, overzealous gardeners who wash off the shrubs aid the disease by keeping the leaves wet for too long. A general guide is this: Ensure rose leaves dry before dusk.

Each orange colored pustule on the backs of the leaves are clumps of very tiny spores. The wind blows the spores to healthy leaves where new infections can start.

Management includes the following cultural techniques:

- Plant the rose in an airy site, with excellent air circulation. (Unfortunately, roses planted against a wall or fence receive poor air circulation.) If needed, increases air circulation within the shrub by removing some of the canes.

- Removing infected leaves early in the season may help limit new infections that season.

- Rake and destroy all fallen and dead leaves.

- Prune out infected and dead wood during the dormant season.

- If you’re considering replacing this susceptible rose, or when you purchase additional roses, ask the garden center which roses tend to be tolerant of rust and other diseases common in our region.

Appropriate sprays can help limit rust on roses, but only when combined with the above cultural strategies. Sprays must be applied prior to infection, or at the very first appearance of rust. Products available to home gardeners are Bayer Advanced Disease Control and Spectracide Immunox. Follow label directions for dilution rates and timing of applications.