Black Spot and Other Common Rose Diseases and Pests Every Gardener Should Know

Roses are among the most widely grown and gifted flowers across the world. They have endured the ages, but that doesn’t mean they are immune to pests or disease.

While modern roses have been bred to be more disease and pest resistant, there is hardly a way of stamping the vulnerabilities out altogether. 

Some varieties are highly susceptible, and while the best defense is to keep a rose plant healthy to begin with, you cannot eliminate the risk entirely. 

In order to ensure your roses bloom in all their glory year after year, you need to know how the pests and disease come to take hold of your plants. 

This guide outlines exactly why these problems decimate rose populations and growth, and exactly what you can do about it. 

At A Glance: Rose Plant and Garden Problems

Pests are insects and small animals which eat plant tissue such as leaves, while diseases inhibit growth and their natural functions, usually caused by pathogenic microorganisms.

While you can’t spot those with your naked eye, you can see the damage they leave behind. 

If either are left untreated, the plant’s health will decline until it dies. These can also spread to other plants, decimating gardens and contaminating compost heaps, spreading the damage even further.

In roses, the foliage is usually the most targeted area of the plant, but the roots, blooms, and stems are also vulnerable. 

If you grow several roses in proximity, these infections can jump from plant to plant, inhibiting growth and creating poor flowers, if any.

Knowing the difference between pests and disease is useful because the treatment for each is different. 

While you’ll always see people walking around admiring their gardens, and stopping to ‘smell the roses’, this also has a practical purpose. 

Keeping an eye on your plants is one of the best ways to stop pests and disease from taking hold when you catch them early.

A combination of preventative measures and the right treatment will ensure that your roses are happy and healthy throughout their life. 

If you use pesticides – using organic is the only way – otherwise you can upset your garden’s ecosystem, kill bees, and create a whole host of problems down the line when it comes to the health of your garden. 

Black Spots on Rose Leaves

Black spot is the biggest villain when it comes to diseases that roses are susceptible to. It inhibits the rose’s growth, leaving it stunted and prevents the plant from blooming prolifically, if left unchecked.

The thug responsible is a fungus, known as Diplocarpon rosae, which targets the foliage. While it can attack any rose at any time, this sort of fungi tends to appear when there is too much moisture, humidity, or not enough sunlight to deal with either.

These fungal spores germinate in spring, and spread through water, insects which act as carriers, and through soil. 

You’ll recognize black spot by the well, black spots on the upper surface of the rose’s foliage. These leaves will turn yellow, and when they fall to the ground, it spreads to the base of the plant and through the soil.

If left untreated, the rose will drop pretty much every leaf, and this will starve the plant of nutrients and food.

While a lot of rose cultivars are very resistant to black spot, there is always a balance in nature. Black spot has developed new strains which are more aggressive than in the past.

While you cannot eradicate black spot from infected roses completely, you can manage it fairly easily. 

The first thing to do is to remove and destroy any leaves with black spot – don’t, for any reason, put them on your compost heap, as you’ll only spread the disease! Cut back any adjacent stems, as this will stop it from taking hold on those, too.

Younger leaves can then be protected by a fungicide, but you should use this sparingly, as it can be very harmful to the environment. Avoid using it at all in windy weather, as this can invite disaster.

But how do you treat black spot naturally?

How To Naturally Treat Black Spot on Roses

Mild infestations of black spot can be combated with a mixture of baking soda and water. 

Water your roses at the base and avoid getting water onto the leaves to help prevent black spot from appearing in the first place. 

The best time to water is in the morning, so the leaves have a chance to dry, and you won’t scald the plant with the sun being directly on your rose plant. 

The best position for roses is in full sunlight, which not only will prevent black spot from forming, but you’ll also get more roses. In most cases, cutting off any infected leaves will stop the fungus from spreading and leading to plant death.

You can also prevent black spot by planting more resistant varieties, such as ‘Roald Dahl’, ‘Hansa’, and ‘Dame Judi Dench’. Most modern varieties have a greater resistance than older roses, but this is not true of every type. 

As is often the case, preventative care is the best cure! 

Common Rose Pests and How to Eradicate Them

When it comes to pests, there are several that can decimate roses. It makes the plants themselves sound all too vulnerable, doesn’t it? 

You might wonder why you should bother growing roses in the first place, but for the most part, roses are very easy to take care of, and most pests are easy to deal with. 

Aphids

Aphids are tiny menaces that can cause a lot of damage. They feed on the plant’s sap, bleeding out the plant’s energy and vitality. 

If you see one, there’s always more, and like most bullies, they crowd together in groups.

Plants infested with aphids can show discoloration on the leaves, as aphids themselves secrete a substance which grows mold. Ergh. 

They also carry a number of diseases and cause flower buds to drop, and new leaves can be deformed. All the more reason to get rid of aphids as soon as possible.

Luckily, aphids also have a number of natural predators, including orange-and-black soldier beetles, and ladybugs. If you wanted, you could order ladybugs off the internet to control an infestation! 

Or, simply crush the aphids by pinching them to the leaves (wear gloves when you do this!) or spray the leaves with water. Any large infestations will mean it’s easier to prune the affected parts. 

To stop rapid shoot growth during peak aphid season, use a slow release fertilizer. 

Rose Midge

Rose midges are white fly larvae which often group around the bases of rose buds. Their presence means that the flower buds will not open very well – if at all. 

With a small infestation, you can try crushing these midges, but more often than not you’ll need to remove the infected plant parts. 

Rose midges also live under the surface of the plant’s base. To prevent another bout of rose midges, you can either apply insecticide to the soil – which will also kill any beneficial insects – or remove part of the soil and replace it.

Rose slugs and Sawfly Larvae

You can recognize rose slugs more by their damage than their appearance, as they can blend in with the leaves. Sawfly larvae and rose slugs are the same thing.

They attack in late spring and the early part of summer, reducing healthy leaves to skeletons if the plant is left to fend for itself. 

The best way to get rid of these is to remove the infected leaves entirely, slugs and all.  

Thrips

Thrips are miniscule orange insects which have long bodies, and you’ll often find them making mischief at the base of rose buds. 

Best case scenario, infected rose buds don’t open, as they look much worse when they unfurl their stained and deformed petals. 

It’s very difficult to remove thrips buried within the rose buds, so steel yourself and remove the buds altogether. 

Caterpillars

Caterpillars chew on buds and leaves, and if you don’t spot the menace themselves, you’ll see the holes that they leave behind. 

It’s easy enough to remove these by hand, and you can even just pop them on the leaves of a weed, or somewhere they can’t cause any harm to your roses. 

Natural predators will usually stop these caterpillars from becoming a complete nuisance, and it’s always better to leave nature to it, rather than upset the delicate balance of your garden’s ecosystem. 

Cane Borers

Cane borers are moth larvae which are white or yellow, and get into canes through wounds. You’ll see the damage in new shoots wilting, the cane swelling where the borers hide, and leaves and stems dying. 

Any affected area of the plant needs to be removed and disposed of. You’ll need to cut along the swelling, to make sure there are no borers hiding anywhere. 

To prevent this pest from taking hold in the first place, you can buy plant wound paste, and you should apply it on any cuts or open wounds.

Leafcutter Bees

Leafcutter bees aren’t pests, but they do like using leaves to help build their nests. You can see the small holes where they’ve taken bits out of the leaf, but this won’t damage the plant, as they don’t take enough to harm it.

You can remove these leaves if you prefer, but let the bees ‘be’.

Spider Mites

These horrible insects are killers of houseplants and garden plants alike. 

While they are microscopic, you can spot the tiny webbing which appears on the underside of leaves, and if you see a hint of bronze on a dry leaf, these guys have moved in. 

One of the easiest ways to remove them is by using water to blast them off the plant. Ladybugs also eat spider mites. 

You can also use a pesticide, but they are becoming increasingly resistant, so water is the best way, and won’t harm the plant or microorganisms living in the soil.

Rose Curculio

Rose curculio weevils have an interesting appearance, with very large, pointed snouts, and they are responsible for making rose petals and buds look like Swiss cheese. 

These nasty little fellas are easily removed – you can hand pick them off the plant (make sure you don’t throw them to the ground – dispose of them, as they will otherwise just crawl back up your rose plant), or mix a solution of mild soap and water, and spray directly onto the rose buds.

Other Rose Plant Diseases and Their Remedies

Powdery Mildew

Another disease that roses are very vulnerable to catching is powdery mildew. 

It’s caused by fungi under the Ascomycota category. More often than not, the soft growth of new shoots is what it targets the most. 

The ideal conditions for powdery mildew is humidity, and a windy day, both of which promote the mildew’s growth and can help it spread to other plants.

You can recognize powdery mildew by the white or gray powdery coating it leaves on new foliage, shoots, and flower buds. It stunts the growth, and makes the leaves curl and die.

If you spot even one leaf or plant part covered in the stuff, remove it immediately – and dispose of it. 

Don’t compost it or put it in a garden waste bin, but the general waste. Otherwise, you risk spreading the disease. 

You’ll also need to spray the whole plant with a sulfur-based fungicide. This will stop the disease from spreading. 

It’s also a good idea to hold off on any maintenance that will promote new shoots, such as cutting back or fertilizing the rose, as these new shoots will be very vulnerable to powdery mildew, and the disease could make a comeback.

Some varieties of roses are more susceptible to powdery mildew than others, particularly red roses. 

If you live somewhere with a lot of humidity, choose a more resistant cultivar, as some have been specially bred to be more resistant than others.

Rust

Rust looks exactly like it sounds. Reddish orange, coppery or yellow spots appear mainly on leaves. While you might think this is easy to notice, they often appear on the undersides.

It’s always a good habit to get into – to check the undersides of leaves for pests and diseases, as by the time they are visible on the outside, they are more difficult to deal with.

Rust spreads rapidly, and affected leaves will wilt and die before their natural lifespan comes to a close. 

Rust is caused by fungi which come under the Uredinales category, and they only form on living hosts. 

The spores of the fungi can spread through soil, so any affected leaves must not be allowed to reach the floor. You’ll have to burn the affected plant parts, or dispose of them very carefully.

Rust forms in moist air and cooler temperatures, so make sure to plant your roses somewhere the air circulation is good, and in full sun.

Botrytis Blight

Botrytis cinerea is a fungus which causes botrytis blight, and this most often affects hybrid tea roses, stopping them from flowering.

You can spot this disease from looking at the rose buds, and if the disease is present, they’ll be covered in gray-brown mold. 

The few flowers that open will have wilted petals, and the color will be stained with yellow or brown. The stem will also be discolored.

Botrytis blight is at its worst during heavy rainfall. You’ll need to cut away any affected parts of the plant and dispose of them, and always disinfect your tools after use.

To treat botrytis blight, use a fungicide especially formulated to get rid of the infection. If your roses are severely infected, you can also use pesticides that contain Bacillus subtilis, which will help.

Spot Anthracnose

Caused by a fungus called Sphaceloma rosarum, spot anthracnose looks very similar to black spot, and all parts of the plant which remain above ground are affected.

Spot anthracnose forms on the leaves as a reddish colored spot, the middle of which will turn gray with a red ring. It will then crack or become a hole. In its early stages, it can look like insect damage.

Keeping roses far enough apart from one another will help keep a good air flow, which is one of the main ways to prevent spot anthracnose. Preventing old leaves from sitting on the ground around roses will also help stop this disease from taking hold.

Common Stem Canker

You can recognize this disease by reddish brown spots appearing on the thick base stem of your rose plant. Wounds on the stem, from scratches to nicks to gaping cuts, are all ways this disease can take hold. 

These spots turn brown, and shrivel into the stem, and make it crack. It can also spread to the leaves, which eventually lead to plant death.

There is no cure for this disease. One way you can help it from spreading is to prune it back, past where the canker begins. Sanitize your tools, and again, dispose of any infected material carefully.

There are, at least, several ways to prevent it. Make sure that no rose stems can rub against each other – this is a big one. The abrasion causes injury to both stems, and invites stem canker, among other things, to take hold. 

The fungus is also spread in soil, so don’t repurpose compost, as this will spread disease from plant to plant. There are exceptions as to when you should, but it definitely does not apply to compost where plants have suffered from disease.

Plant any unaffected roses in fresh compost, preferably in a container or in beds away from where the original infection occurred.

Crown Gall

Crown gall affects many plants, but roses are one of the big ones. It’s caused by a bacterium called Agrobacterium tumefaciens, and it’s a very noticeable infection.

The plant swells at the crown – which is the part of the plant that pokes just above the soil – and you’ll see tumor-like growths appear. This nasty little bacterium actually transfers part of its own DNA into the genome of the plant. 

While some would argue that crown gall doesn’t decimate the rose, it changes the plant’s metabolism. It also causes your rose to get weaker, the growth becomes stunted, leaves discolor, and new shoots die back.

If left untreated, crown gall tumors will become woody, and more will form. It can leave your rose plant vulnerable to more disease and injury caused by cooler temperatures, and it will eventually kill the plant. 

This bacterium lives in the soil naturally, and its ‘job’ is to decompose organic material. It can live for years without affecting your plants, so long as there’s no injury which will attract them into the wound. 

Usually, infected plants are destroyed. You can cut out the galls, and submerge the lower part of the plant in a solution of streptomycin for a few hours, after which you can replant elsewhere. Remember that the soil is contaminated, so don’t plant it in the same place.

Mosaic Virus

Mosaic virus slows the growth and metabolism of your roses, and it will eventually cause plant death. 

You can recognize it by the leaves becoming mottled and yellowed in places. While the signs can disappear on their own, if they get worse, you’ll need to pull up the entire plant.

Heat and Winter Freeze Damage

Extreme weather can also adversely affect roses. All of a sudden, roses don’t seem so robust now, do they? There are things you can do to limit the damage, however.

Long periods of hot and dry weather will cause leaves to brown, but you can counteract this by giving your rose a good soaking in the early morning or evening, so long as the sun isn’t directly on the plant.

Extreme winters can also damage your plants. The canes can turn brown and die in extreme temperatures, and potted roses need to be kept either near the house to absorb residual heat, or in a greenhouse.

You can also protect your roses with horticultural fleece, but this should only be done if you’re expecting the weather to be extreme.

Environmentally Friendly Pest and Disease Treatment

One of the easiest ways to prevent common rose pests is to diversify your planting scheme. Plant a wide variety of flowers such as scabious, eryngiums, borage, and goldenrod which will attract natural predators, and keep your garden’s ecosystem in balance. 

Pesticides – while useful, and quick to act – can build up in the soil, and can enter waterways, which harms us, animals and plants. It can also kill your plants altogether.

Being mindful of not upsetting the ecosystem of your garden goes a long way to keeping it healthy, as nature often has the solutions to the problems it creates. 

Botanical insecticides such as neem oil and pyrethrin, and using beneficial insects can also prevent infestations. When it comes to pests and diseases, prevention is the best cure.

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