While roses are surely the queens of any garden, they are unfortunately susceptible to several different types of diseases. Most diseases can be avoided by purchasing certified disease-free roses and good preventative gardening measures, like choosing an appropriate spot, preparing the soil, and ensuring spacing, drainage, and maintenance. Sometimes, though, we just get unlucky and end up with rose bush diseases anyway. Then what?
Read on to learn about 7 common rose bush diseases, and how to cure them!
7 Rose Bush Diseases
1. Black Spot
Black spot is one of the most common rose bush diseases. As you might imagine, you can spot the disease when it manifests as black splotches along your roses’ leaves and stems. Black spot usually starts at the base of the stem and then slowly climbs up to the rest of the plant, however, so by the time you’re seeing it on the leaves, chances are it has spread throughout the plant already.
Black Spot is caused by the diplocarpon rosae fungus, and while it probably won’t kill your roses on its own, it will cause defoliation and weaken your bushes. Think of it like a lowered immune system in a human—because your roses are weaker, they have a lowered defense system against tougher diseases and harsh environmental conditions that will kill them.
This rose bush disease spreads through water: when water splashing on an infected plant also dampens a healthy neighboring rose. For this reason, the disease usually emerges in the fall through spring, when it’s more likely for rainwater, mist, and dew to stick around and not evaporate as quickly. That means that Black Spot is less likely to occur, and will certainly not spread, in dry 80-degree Fahrenheit weather and above.
Black Spot can be treated with commercial sulfur-based fungicidal spray, or you can make your own at home by mixing a teaspoon of baking soda and a quart of warm water. The more advanced the disease is in your rose bush, the harder it is to eradicate, so make sure to keep an eye on your roses to treat Black Spot as soon as it appears!
2. Powdery Mildew
Powdery Mildew is another very common rose bush disease, also caused by a fungus, which particularly impacts young leaves. When the disease strikes, young leaves become misshaped and turn purplish. At an advanced stage, the diseased leaves will also develop a white powdery fuzz along their surface.
Unlike Black Spot, Powdery Mildew is airborne and thrives on unstable weather. That means that roses are most susceptible to Powdery Mildew when cold moist nights are preceded by warmer dry days. The disease also has a harder time spreading when the leaves on a rose bush are wet or moist.
Consequently, some gardeners believe that the best preventative measure for this nasty rose bush disease is by keeping their rose bushes continually wet. This is not a good solution, however, because the moisture makes it easier for other diseases to spread: for example, Black Spot, as explained above.
As with most things, the best cure for Powdery Mildew is thorough prevention. Use fungicide on young leaves and new growth, and plant your roses in a location with good ventilation for the purpose of avoiding both diseases carried by the wind, and to dry off excess water. If Powdery Mildew still strikes, cut away impacted parts of the rose and use more fungicide to sanitize the salvaged parts.
3. Crown Gall
Able to survive 15 to 20 years in the soil, Crown Gall is a bacterial rose bush disease that doesn’t just affect rose bushes. but other plants as well. Its symptoms include the growth of brain-shaped dark masses at the base of stems of affected plants. Young Crown Galls start out pale and round, and take on their recognizable texture and color later on. They can be anywhere from quarter-sized to fist-sized masses, and as you can imagine, cause severe growth problems for the plants.
The disease is spread through water and infiltrates the plant through wounds and breakage, which sometimes happens during handling, transplanting, and/or pruning. Crown Gall can sometimes be confused for graft unions or normal swellings that take place during a flower’s budding process, but time always tells the difference, because Crown Gall will continue to grow.
Unfortunately, there is no cure for Crown Gall, so your best bet is intentional prevention and making sure the disease doesn’t spread if you spot it on one of your plants. Always check rose stems for suspicious growths, and only purchase certified disease-free roses. You could also dip the ends of your roses in Galltrol-Am which is sometimes used for Crown Gall prevention.
If a rose bush, or any other plant in your garden, nevertheless becomes infected, dig it up and discard it in a location that won’t come into contact with the rest of your garden (not your compost!). Because, as mentioned earlier, this stubborn rose bush disease can survive underground for up to two decades, it is strongly advised not to plant anything else in that same spot for at least five years.
4. Rose Rosette Disease
Rose Rosette disease used to be rarer, but has now become a more common rose bush disease that causes lots of issues to rose gardeners, even though it remains obscure. The pathogen has yet to be identified, but experts have concluded that Rose Rosette spreads through a parasitic mite called eriophyid.
The symptoms are odd, but very recognizable, to say the least. An infected rose will start to shoot out dense and dark red leaves, nicknamed “witches broom.” Their bushiness is deformed and remains short despite the rapid growth. The rose also grows more thorns than expected.
Though these symptoms aren’t entirely pleasing to the eye, if they ended there, Rose Rosette would be less of an issue. The problem is that diseased plants are weakened and, as the disease advances, ultimately die.
Unfortunately, this is another rose bush disease for which we have yet to find a cure. By the time the disease is identified, it is too late for any kind of spray to be effective. Just like roses infected with Powdery Mildew, the best course of action is to remove the plant in its entirety, including roots, and disposing it far from other plants it could potentially infect. Some have suggested controlling mites, which are the carriers of the disease, as a preventative method, but this has anecdotally not led to any success. So we’re back to the golden rule: buy certified disease-free roses!
5. Rose Mosaic
Rose Mosaic is a rose bush disease caused by one of two viruses: prunus necrotic ringspot virus and/or apple mosaic virus. The symptoms can manifest in odd yellow discolorations: yellow patterns of wavy lines or yellow splotching on leaves, or just a general yellowing.
There might also, however, be no apparent symptoms, and the plant just weakens and declines in health. The yellowing could also just appear on one part of the rose bush, but even if this happens, the entire plant is infected and will have growth problems.
The virus spreads through vegetative propagation (asexual plant reproduction from a part of a parent plant) and through insects, like aphids. Sometimes, you might even accidentally spread the virus by using the same pruners you used to prune infected plants on healthy ones. Take care to disinfect your pruners, because plants that are infected by viruses cannot be cured. Luckily, however, plants alone cannot infect each other without some sort of external intervention!
As usual, the best cure here is prevention. Try to plant certified virus-free roses, and do some insect control. If you still find Rose Mosaic in any of your rose bushes, remove the plant and dispose of it far away from your garden!
Rust is yet another rose bush disease caused by a fungus. As you might imagine, symptoms of the advanced disease make it seem as if the rose is rusting: you will find orange powder both on the leaves and cane of the plant (everywhere except for the petals) and on the soil beneath it. Some severely diseased roses could even lose their leaves after they’ve turned yellow or brown. During the winter, affected canes could even darken, closer to black.
Though perhaps it offers little reassurance, you should be glad to hear that Rust only impacts roses, so know that even if you spot the orange dusting, you won’t run the risk of infecting your other plants.
Though at this point you probably know the “cure” to any rose bush disease by heart, it bears repeating: the best cure is prevention. That means leaving enough space both among the rose bushes themselves and between the bushes and other plants. It also means ensuring that the space they grow in has good air circulation, that you’re promptly dispatching any sickly leaves or plants in the vicinity, and that you’re pruning wisely.
It’s also a good idea to water your plants in the morning so that any water left on their leaves can dry before nighttime. Then, apply fungicides that contain mancozeb, propiconazole, chlorothalonil, sulfur, or myclobutanil preventatively rather than waiting for the problem to show up!
Last but not least, Cankers are a rose bush disease caused by yet another fungus that impacts roses. They are a symptom of plant stress. Cankers usually manifest as brown, misshaped, and or strangely textured areas along the canes. Sometimes you’ll be able to see tiny black spots within the Cankers.
Once a cane has been infected, it will die, and the surrounding leaves will also wilt. Luckily, though, a Canker doesn’t always infect the rest of your rose plant: simply cut away the affected area, making sure to prune well below it and not leave anything behind.
There is no cure for Cankers besides amputation. To best prevent the formation of Cankers, make sure to not cover or mulch your roses too early before the winter, which could trap too much moisture and worsen Canker symptoms. Keep your roses healthy and be proactive in their health, growth, and pest and disease prevention.
Wrapping Up Rose Bush Diseases
As you can probably tell from this list, roses are susceptible to a number of rose bush diseases. The good news is that they are avoidable through informed and intentional gardening. The first place to start is to make sure the roses you’re buying are certified virus and disease-free!
Interested in more rose content? Check out our blog’s rose bush section!