Hello, yesterday I noticed orange raised spots on the underleaf of some rose bushes. Two weeks ago they were not there when I pruned these roses. The raised spots were throughout specific rose bushes. I take great care not to encourage disease among my roses. I cut down the diseased roses once again. I removed all cuttings, collected the debris from the earth and sanitized my secateurs. What should be my next move? Should I spray the diseased roses with Dormant Oil or with a rose fungicide that treats rust. If the disease returns I’m thinking of digging out the roses and throwing them in the garbage. What are my options. I do not want the rust to spread to my other rose bushes. I have never experienced this disease before. Thank you.
Thank you for contacting Toronto Master Gardeners.
I’m so sorry to hear about your diseased roses. Growing healthy roses can be a challenge. Given your description, your roses may have rose rust disease which is caused by rose rust fungus (Phragmidium fungus). The most characteristic symptom is the appearance of orange pustules on either the upper or lower leaf surfaces, commonly occurring in late spring and again in fall. The fungus spreads through both air and water. Note that this rust only attacks roses. Left untreated, rust spots on roses may eventually kill the plant.
Recommended steps to prevent/control rose rust include:
- Fungi and bacteria require high humidity to produce more inoculum. Therefore, good air circulation within and around rose bushes is critical for preventing rose rust and other diseases. Make sure your roses are correctly spaced apart and well pruned so the leaves will dry out quickly after a rain.
- Water your rose bushes at the soil level (not on the leaves), a drip irrigation system would be ideal. Water in the morning so any water on the leaves has time to dry out during the daytime.
- Ensure your rose bushes are planted in a sunny location, ideally getting 6 hours of sun daily.
- If/when your rose bushes display symptoms of rose rust, apply a foliar fungicide as needed to control the rust, following the manufacturers application instructions carefully. You can purchase a suitable fungicide at most reputable garden centres.
- Dispose of any infected leaves to prevent spread of the fungus to other rose bushes.
- Sanitize any garden tools you use to prevent spread of the disease – a bleach & water solution works well (proportions for a solution can be found online).
- The spores of rose rust fungus will overwinter in leaves and repeatedly re-infect the rose bushes the following spring. Make sure you rake and dispose of all old rose leaves as well as other garden debris from around your plants.
- If you do decide to replace any of your rose bushes, note that growers have produced rose cultivars that are resistant to rose rust disease. Look for these cultivars with your next rose bush purchase. Rugosa roses and some of the David Austin cultivars are generally resistant to rose rust disease.
Good luck and I hope that you’ll be able to enjoy your beautiful rose bushes this summer.