By the end of every fall I find myself swearing off roses. But at the beginning of every summer to follow, they suck me back in.
The promise of gorgeous flowers and carpets of petals, and the delectably tedious art of pruning, makes the headaches over diseases that commonly affect these plants tolerable.
At least until the end of fall, that is. Then I give up on them again.
But such is the life of the gardener.
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Few plants in the garden offer the refined payout that roses do. From their iconic flowers to their euphoric aromas, these plants are a mainstay for a reason.
But this comes at the price of requiring lots of attention to detail in terms of plant health and care.
If you grow roses, you’re almost guaranteed to encounter disease.
Seasoned experts and eager amateurs alike are going to encounter black spot, mosaic, and mildew growing on their roses at one point or another.
Let’s take a look at these common and likely problems you’ll discover, and learn how to address them. But first, we’ll go over a few basics on disease prevention.
Here’s an overview of what I’ll cover:
What You’ll Learn
Tips for Preventing Disease
Roses want full sun conditions and lots of airflow. They also thrive on being doted on, so regular pruning and removal of dead tissue will help minimize the risk of disease.
Hey, roses are a lot like us, aren’t they?
Try planting disease-resistant cultivars to start with, to reduce the likelihood of infectious encounters.
I have never been a fan of Knock Out® roses myself, but they are a popular series because they are generally highly resistant to disease.
Chemical Solutions
Always follow the directions on the label of any chemical solution you use in your garden!
Too much or too high of a dosage is just as bad, or sometimes many times worse, than applying too small of a dosage. Always refer to the label when using any chemical.
On the same note, if you find a strange tip on the internet or in conversation with a fellow gardener, do a little research before following through with it.
As much as I’m a fan of old school gardening techniques, I find too much of this is fluffy nonsense.
Keep Those Pruners Clean ‘n’ Sharp
I sharpen my pruners every single morning, and if I’m doing a lot of snipping, I’ll bring the whetstone with me to the jobsite.
A sharp blade makes a clean cut, and clean cuts minimize damage to a plant while simultaneously helping to prevent infections.
Many rose diseases easily spread to other plants, oftentimes from a gardener’s pruners.
I carry a spray bottle filled with rubbing alcohol and spritz my pruners between every plant I prune, or sometimes between every few cuts on the same plant.
It’s tedious and annoying, but it’s vital to plant health.
9 Common Diseases
These are some of the more common diseases the home gardener may encounter.
1. Black Spot
One of the most common diseases you’ll find on your plants is black spot.
Caused by the fungus Diplocarpon rosae, black spot will defoliate and weaken your roses, making them more vulnerable to other environmental pressures.
Think of black spot as a gateway disease; it is unlikely to kill your roses by itself, but it stresses your plants and makes them more susceptible to other infections.
This fungal issue is often encountered in the spring and fall, when conditions are wet and cool nights prevent moisture from evaporating.
Warm weather over about 80°F (26°C) tends to prevent black spot from occurring in the first place, and dry weather inhibits the progress of this disease.
Water splashing on infected leaves is what spreads the fungus, so a lack of precipitation and unnecessary irrigation means minimal spread of infection!
Black spot often begins its damage at the base of the plant and works its way to the top.
Infected leaves will develop a telling bunch of black spots before the plant drops these leaves. Infected canes will look bruised and take on a black or purple hue, indicating the presence of infection.
The fungus overwinters in infected leaves and canes, so if your plants have it one year, it’s likely to make an appearance again in the future.
How to Handle Black Spot
Black spot can be treated with a few different types of sprays. However, this is a very difficult disease to handle once an infection sets in, so early care is vital.
A mixture of about a teaspoon of baking soda with a quart of warm water can be sprayed on the plants, or you can use a sulfur- or copper-based fungicidal spray.
I use this product from Southern Ag, and found the results promising. It’s available on Amazon.
Neem oil can also work, but I tend to avoid it when working with roses to prevent causing harm to beneficial insects.
Find more tips on treating Diplocarpon rosae here.
2. Botrytis Blight
I remember watching some tea roses expectantly, eager to see their developing buds blossom into the lovely flowers I’ve come to love (and detest, depending on what time of the year you ask me about it…) then furrowing my brow as the petals turned brown and crispy.
This was my first encounter with botrytis blight, an awful and ugly disease that most often attacks tea roses, ruining their blooms.
Like most fungal infections, this one is caused largely by environmental issues, so a hot and humid summer is the perfect breeding ground for this disease.
Handling Botrytis Blight
While botrytis blight can be controlled temporarily with fungicides, it often adapts a resistance to these sprays which makes them ineffective after prolonged use.
Sunny, dry weather is often enough to keep this condition under control.
An interesting solution to handling botrytis blight rests in your fertilization practices.
Too much nitrogen can create an abundance of new, soft growth that is overly susceptible to this blight.
Limit any midsummer feeding you provide to help minimize the risk of blight attacking that new growth.
3. Cankers
This one is an ugly, potentially fatal fungal infection.
Canker reveals itself by turning the canes black, most notably in locations where the plant was recently pruned.
Always clean your pruners between different plants to prevent this from happening!
Interestingly, cankers often cause the most trouble during the colder periods of the year, making them a bit more difficult to notice than other diseases.
I’ve encountered them during early springtime pruning, either by discovering old cankers, or noticing new ones taking hold.
Roses are susceptible to three types of canker:
1. Brown Canker
Brown canker is caused by Cryptosporella umbrina. You’ll find tiny, raised, reddish-purple bumps on the canes, a little less than half the size of a grain of rice.
As these little spots begin to mature into their fruiting bodies, they develop a brown or black color.
2. Brand Canker
Caused by Coniothyrium wernsdorffiae, these have a similar reddish color as the brown variety, also found on the canes, but these cankers quickly develop a brown center.
I’ve yet to see a brand canker without that brown central coloration.
3. Stem Canker
Sometimes harder to spot at a glance than the others, stem canker, caused by Paraconiothyrium fuckelii (formerly Coniothyrium fuckelii), tends to have a yellowish color, but it can also swing towards the red slice of the color wheel.
This type of canker shows up on the bark.
Handling Cankers
Using clean, sharp pruners, remove the infected tissue and canes.
I’ve seen people cut two to three inches below the infected tissue, but I go farther than that if it’s a widespread issue, sometimes removing 75 percent of an infected stem.
Cut into the healthy, green area of the plants, and follow up with a fungicidal treatment to give your roses an added boost against reinfection. Make sure you sanitize your tools after each cut.
Preventing cankers is surprisingly easy: mulch their roots to prevent the plants from getting too cold in the winter, and make sure you provide adequate amounts of fertilizer.
4. Crown Gall
Crown gall is serious business. It’s also one of the most easily identifiable of all rose diseases.
Crown gall is an ugly, weird-looking growth of tissue that looks like a mix between a brain, a praying mantis nest, and a head of cauliflower.
It can be a smaller mass of tissue or a larger one, and can occur almost anywhere on the plant, but it almost always develops near the soil level or crown.
It is caused by a bacterium (Agrobacterium tumefaciens, for the Latin lovers) that enters wounded tissue.
Though it’s easy to identify once you spot it, most of the time, this disease is not noticed until weeks after the date of infection.
Handling Crown Gall
Well, this one is simultaneously easy and sad: remove the infected plant and destroy it, and do not plant another rose in this location for two years.
The goal here is to get rid of any residual bacteria in the soil, and any of the original plant’s infected roots, before replanting in that area.
Treatments are available to slow the growth of a crown gall and to minimize its damage, but these efforts will not kill this infection.
Treatment only slows the progress of the disease and is not recommended.
5. Downy Mildew
Caused by the water mold (oomycete) Peronospora sparsa, downy mildew commonly shows up during cool, damp weather.
Rain, humidity, and temperatures between 59 and 64°F are prime conditions for infection.
The pathogen spreads via splashing water and wind, and plants that are overcrowded tend to be most susceptible.
At first, you might confuse the symptoms of downy mildew with those of black spot: purple or dark brown lesions on the surface of the leaves, stems, and/or flowers.
As the disease progresses, spores will develop on the undersides of the leaves forming a mildew-like covering.
Handling Downy Mildew
Keeping your plants well-spaced and pruned to prevent the build up of moisture and watering at the soil level rather than on the foliage will go a long way to preventing this disease taking hold.
If you do find your roses are infected, you can treat them with copper fungicide.
Find tips on managing downy mildew here.
6. Rust
A common problem caused by nine different species of fungi in the Phragmidium genus. At its most benign, rust is an ugly condition.
But in the worst cases, it will kill the initial host plant and spread to the others.
It’s relatively easy to spot rust on your roses.
They’ll often drop leaves, and the condition is obvious with its orange, rust-colored marks that appear on leaves and canes. In the winter, infected canes tend to turn black.
Rust overwinters in infected tissue, but it can also find a safe hiding spot on trellises and fences, or just about any place near the host plant where it is offered some protection from the worst of the winter weather.
Luckily, this fungal issue is specific to roses, so it should only pose a potential threat to the other Rosa species in your garden.
Handling Rust
As is the case with many plant diseases, a thorough and attentive watering regimen is key to solving your rust issues.
Remove fallen leaves every autumn and as an early spring cleanup project to help minimize the spread of this fungal disease.
If you’re in the planning stage of your garden design, consider purchasing rust-resistant varieties to dramatically minimize your chances of encountering this annoying problem.
If you opt for chemical control, consider using Bayer Advanced Disease Control instead of a combination fungicide and insecticide.
Bayer Advanced Disease Control
This is a reliable and readily available over-the-counter choice, and you can find it on Amazon.
Learn more about dealing with rose rust in our guide.
7. Powdery Mildew
If you’re growing roses, you’ve probably encountered powdery mildew before. It leaves a telltale… well, powdery mildew on the leaves, a gray coating that screams “yuck!”
It’s commonly spotted in a variety of plants in the garden, and becomes an almost constant annoyance in late summer and early fall.
This fungal disease thrives in humid conditions where airflow is minimal or nonexistent. Sounds like every summer day in Philadelphia, if you ask me!
However, it can also thrive in dry conditions, and that’s what makes powdery mildew such a headache. You just never know when it’s gonna strike.
If it’s a minor case of powdery mildew, I tend to let it go unmended, but will pay close attention to infected pants to ensure the disease doesn’t spread.
Oftentimes this is an issue that will take care of itself in minor cases.
A thorough fall cleanup of all shed leaves is a helpful trick to minimize any recurrences.
Handling Powdery Mildew
Either of the fungicides recommended for the previous fungal issues will help to treat powdery mildew.
Make sure you’re spraying all parts of the plant, including the tops and bottoms of leaves, on a regular schedule.
Some experts recommend an application every two weeks, but as always, read the label of your purchased chemical for its suggested usage.
Find more info on controlling powdery mildew on roses here.
8. Rose Mosaic Virus
Rose mosaic is caused by a number of different viruses that are collectively known as the Rose Mosaic Viral Complex (RMVc).
Symptoms generally include discoloration and mottling on the foliage and flowers. As the infection advances, growth may be stunted and plants may fail to bloom.
This disease is spread by insects, and a plant may be infected for many years before becoming symptomatic.
Handling RMVc
Unfortunately, there is no effective treatment for rose mosaic. The infection is systemic and pruning away discolored foliage will not help – except, of course, to make your plant look better.
In the case of a severe infection, the only thing to do is to dig up and destroy affected plants, and only grow certified disease-free specimens in their place.
Check out our guide to learn more about RMVc.
9. Rose Rosette
Also known as witches’-broom, in my opinion, this is the saddest-looking disease a plant could possibly develop.
It’s as if the physical traits of witches’-broom were meant to twist and warp a rose just enough that it’s still beautiful, but in a very ugly way.
You’ll notice this disease, which is spread by a virus-carrying mite, when you see the telltale bizarrely red growth of the plant.
Other early symptoms include deformed and brittle leaves with yellow and red pigmentation.
As the disease progresses, the plant develops smaller leaves and vibrant red shoots.
You’ll also notice a dramatic increase in the number of thorns on the stems of your roses.
They will come to look like something more akin to a wild bramble than your favorite rose.
This disease spreads throughout the summer as the mites travel on the wind and infect new plants, laying eggs over a 30-day period.
Handling Rose Rosette
Witches’-broom tends to infect wild roses far more readily than cultivated ones, but anything in the genus Rosa is susceptible.
It’s recommended that you plant your specimens as far away from wild roses as you can, to avoid transmission.
Prune your roses hard each year (I prune mine on the first decent days of early spring), cutting back as much as 70 percent of last year’s growth.
This helps remove any overwintering mites and potentially infected tissue.
You can also apply insecticidal soap, but be warned that these chemicals kill almost any insect they come into contact with, including natural predators that feed on the mites.
If you’ve got a plant that is infected with witches’-broom, you only have one real option for control: destroy the plant and burn it, or place it into a plastic bag and dump it with the garbage.
I’d recommend bagging the plant before removing it, to prevent spreading the mites as you carry it around the yard.
You can still plant a new rose in the same location, since the disease is transmitted via mites that do not overwinter in the soil.
We go further into identifying and controlling rose rosette here.
Get Ready for Healthy Roses!
Now that we’ve gone over the diseases you’re likely to encounter, you’ll be ready to hit the ground pruning this season and enjoy a fabulous display of healthy blooms.
Still have questions? Please drop us a line in the comments below, or share your own tips and tricks for rose disease management.
Check out our pruning guide to brush up on that skill, and if you choose to apply any type of chemicals to your roses, read our pesticide application guide.
And to read more about growing roses in your garden, try these guides next:
Great guide! I am wondering if you can help me determine if my knockout roses are being impacted by one of the diseases you mentioned. I’m having a difficult time trying to find a disease picture online that matches.
Sure, are you able to upload a photo?
Why does my rose bush look wet and sappy on the leaves? Is it from the wasps that are always around it?
If it looks wet it could be honeydew, which is a nice term for “aphid poop.” If you have wasps flying around the rose bush it’s probably because you’ve got aphids, and the wasps are taking care of the infestation for you. That’d be my guess!
If you look carefully around the plant, on its leaves or the flower buds, you might find the tiny little aphids swarming. The wasps are capable of solving the problem by itself, but if you don’t want to wait, you could pick up some insecticidal soap to get rid of them.
I have searched the internet for weeks about this problem with my roses and have had no luck identifying this problem. As you can see from the photos, the rose looks dead on one side. A couple of weeks ago this plant was perfectly healthy looking and full of blooms. Suddenly the limbs and leaves start dying and this typically spreads to the whole plant. It seems to be contagious to nearby roses. The photo of the monster tomato plant I’ve included is about 10 feet from this rose and is obviously not affected by whatever is affecting the roses.… Read more »
This one’s a little tricky. First off, AWESOME tomato plant, I’m jealous. I try to work backwards with “easiest solution to most difficult solution.” My first question is, is the soil waterlogged? Could be a leaking irrigation line or just too much water from a hose or sprinkler system, or even from rain. Judging from that tomato plant, though, I’d say this might not be the case. Check the stems for damage and discoloration. It’s hard to make out clearly from this photo, but it looks like the central cane in the second picture (the one growing straight up) has… Read more »
I have that too here in Ontario, Canada
Enjoying your guide but cant seem to figure out what’s going on with my always healthy knockout roses this year. Any idea what this could be? Thanks, Angela
That picture looks like you’ve got a pest problem, maybe white flies or something of the like. Any insecticidal soap will take care of pretty much any insect pest issue you have. You can order some online or grab it from the store, or make your own at home. I found a lot of lanternfly nymphs in my backyard and whipped up a quick homemade insecticidal soap. Mix two tablespoons of dish soap to two cups water and add to a spray bottle, give it a shake, and spray those bugs away.
Hi there, I’m trying to identify what’s going on with my roses. They seem fine from afar, leaves and new growth look nice enough, a bit chewed on maybe but that’s life. The stems on the other hand look all damaged, some are woody and cracked and others with brown purplish spots.
Hey Chiara, did you have a wet spring this year? It looks like you’ve got black spot on the canes. Not good, but not the end of the world, either. Roses can take a tremendous amount of mechanical damage (pruning) and still keep kicking through it. In theory you could let them keep growing for now, by itself it’s not a major issue but it can lead to other headaches for your roses. If you don’t want to risk it, you’ll need to grab a clean pair of pruners and simply cut away and destroy the infected canes. Cut it… Read more »
Thank you for the fast response! Yes, rainy April plus my incorrect watering (live and learn). About the pruning, should I do it the sooner the better, or wait, I don’t know, after the blooming? And, most of all, what if the spots go all the way down? Thanks
Live and learn is the gardener’s motto. One of them, anyway. If the spots go all the way down the cane the disease could spread, but that fungicide treatment will help halt the spread for the rest of the season. Next spring, if you enter the garden knowing “that rose had black spot last year,” you’ll be able to stop the problem again before it starts! You can wait to prune until after they bloom. I live outside of Philadelphia and the summers here are just awful. Hot, consistently high humidity is like the rule for this place, so fungal… Read more »
Hoping you can help with my rose bush. I’ve always thought purple leaves were new growth but some said it might have a disease.This bush was purchase and trans planted about 3weeks ago, given rose feed(miracle gro pink box) had about a dozen beautiful blooms, trimmed back some. Now the leaves are a deep purple and has about 10 new buds.
1st photo is after planting
2nd photo is as of this morning
thanks
Luckily that’s just new growth on the roses you’ve got there. Many roses push out purple-hued new growth. It’s very attractive in my opinion, and it will soon turn green to match the rest of the plant. The profuse flowers are probably just a result of being fertilized, nothing to worry about with that either. Good call on watching for that discolored new growth, though, since that’s an indicator of rose rosette disease. However, in that case the new foliage/buds/thorns are obviously malformed and look… well, weird I guess. Like some bizarre surrealist painting of a rose. Your plants look… Read more »
Hi Matt im in UK. I have a David Austin Gertrude Jekyll rose in pot planted in March. It grew and flowered beautifully. Then this happened – I don’t know what is wrong or how to treat it.
Hi Pauline, I don’t see a picture included here, maybe it failed to upload?
I appreciated your descriptions of different pests that attack roses. I have one that I’m nor sure about. I had a small memorial rosebush in my house all winter (NY), and she was healthy and had a bloom in April! On May 30, I put her in the garden, bushy and with a new bud, made certain her roots had water and good compost, and and by June 2, some of her leaves were turning a pale yellow/ash, not dusty, both sides, seem to be creeping higher. I do not want to lose this particular rose. Suggestions?
Hey Susan, I’m wondering if you gave your roses a “breaking in” period. As in, did you decide to bring it outside one day? Or did you bring it back outside for a few hours at a time over the period of a week? It’s important when bringing an overwintered plant outside to do so in gradual steps. Even if the weather feels nice to us it can be a drastic shock for any plant to go from a perfectly controlled climate (indoors) to a world with wind, sunshine, and other factors (outdoors). If this is the case you can… Read more »
Hi, I have a problem with what I think is some kind of rose disease. The almost whole plant got brown and the leaves look like dry. Can anyone help me to identify what the issue is? Thank you!
I also have this issue on my Knockout roses and it has spread to a few others. Interested to learn what the disease is and how to treat.
Ditto here. All three of my Knockouts have this – taken over the entire plant. I’m wondering if there is any chance to revive it?
Check my reply to Milan! Long story short… it might be savable, if you’re proactive and aggressive with removing infected tissue and starting a fungicide treatment, but if the plants are all infected and show no signs of improvement over time, it might be best to remove them entirely and start over.
I replied to Milan above, hope the answer is helpful for you too!
I have this exact same thing! Can’t figure out what it is. Any help is appreciated!
Check the reply I sent to Milan just now! Hopefully it’s helpful for you, and if it’s not please reach out again so we can figure it out together.
It looks like a couple of problems, though it’s tough to make out specifically what. If you could, snap a photo of the canes as well? Without seeing that, though, I feel safe in saying this is a couple of fungal issues all doing damage at the same time, and maybe with some canker issues thrown in as well. First step is to grab some sharp pruners and some rubbing alcohol or a 1 part bleach to 10 parts water solution. You’ll want to cut away all of the canes that are infected. I can see a few… Read more »
Hi! Thanks for all of the great info on rose diseases! I have a yellow and cream knock-out rose that went in the ground about a month ago. It’s in a newly built flower bed. My soil is a pretty heavy clay (as is much of central Pennsylvania soil), but I’ve amended it with a good organic soil, peat moss, and humus. The cream colored roses look great, but the yellow roses on the same plant have tiny black dots. What is this problem?
Central PA, huh? I’m in Delaware County, not far from your neck of the woods. I’m familiar with that clay-based soil, it’s not much fun to work with. Good on you for amending it with the good stuff! I’d guess you got a good amount of heavy rain so far, just as we have a little further east? Those little spots look like black spot, not a big issue especially considering the rest of the plant looks so healthy from this picture. If you want to be active in taking care of it though before it might become… Read more »