Identify and Treat Rose pests and diseases
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Unfortunately, roses are vulnerable to quite a few pests and diseases, and when I think about all the plants I’ve grown over the years, they’re the only plant where I try to prevent diseases in the first place. I’ve had the most success spraying roses with fungicides early on in the season to help prevent diseases like rust, blackspot and mildew. Prevention is much better than trying to treat a disease once it sets in.
The good news is that only a couple of these pests and diseases cause severe damage to your roses. After over 20 years of growing roses commercially, I have put this guide together to help you identify, treat and more importantly prevent these diseases in the first place. When it comes to pests like aphids and rose sawfly, this is more of a identify early and treat quickly. Read on to learn more.
What are aphids?
In the growing season of March through to August, populations of sap-sucking aphids start to make an appearance and usually are attracted to the fresh green shoots. With different varieties of aphids, such as greenfly and blackfly, these insects may look different to each other. The aphids suck the sap out of the rose leaves and cluster on the leaves, flowers and tips of the shoots. They have many natural predators such as birds, ladybirds, and wasps which help to control them so encouraging them into the garden can help.
How to spot aphids
Aphids are generally green or pink insects and are attracted to young foliage and sometimes flower buds. A sign that the flowers or leaves are infested is the white cast-off aphid skins. The leaves can also start to curl, but they can often be missed.
But a more tell-tale clue is a clear sticky substance called honeydew. The aphids secrete this as they suck on your plant. In itself, it doesn’t harm your plant but attracts a fungal disease called black sooty mould and ants.
What to do
It’s usual and natural to have a few aphids on your plants as they’re part of the garden eco-system and a few of them won’t do much harm and can be left. They do have natural predators which snack on them, so they’re usually kept in check naturally, but I like to take a proactive approach and spray aphids before they get out of control with a pesticide. I like to avoid pesticides where possible, but with roses, i find I need to use pesticides to keep them under control and the same with fungicides for diseases. I also like to use a spray like Rose clear which is both a pesticide and a fungicide in one. This means I only need to spray once and it will control both diseases and aphids.
Check your roses from the spring onwards to see if your aphids become an infestation. By late June, their natural enemies (lady birds/bugs, ground beetles, etc.) should pick them all off. Along the way, you can always take them off the plant and squish them with your thumb and index finger.
If your rose’s aphids are really out of control, use an organic spray such as natural pyrethrum or neem oil to control them. These natural pesticides have a short working life, so you must keep reapplying them. Although I rather not, like I’ve already said, I do use pesticides that treat both diseases and pests at the same time.
Rose root aphids
What are rose root aphids?
These are the same kind of aphids as those discussed above. They’re small and brown but feed on the sap on the rose roots and stems close to the base of the plant during the summer.
Rose root aphids spend the winter on stems of the plant that are close to the ground.
How to spot rose root aphids
You may see rose root aphids during the summer at the bottom of your rose tree. But you’re more likely to encounter them in their winter form on the stems at the bottom of the plant. They overwinter as black shiny eggs, about 1mm to 2mm long.
These are fickle insects though. You may find many on your rose tree one year and none the next, not like aphids that make an appearance every year in there thousands.
What to do
Nothing. They don’t seem to do any damage beyond sucking on the sap of your rose plant and its usually not serous enough to cause any real harm. They’re part of your garden’s natural eco-diversity. And they provide food for a range of predators as they have many natural enemies.
Destroy the eggs when you find them in the winter. Maybe make looking for them part of your annual pruning task.
Pesticides and insecticides don’t have any effects on these aphids.
Rose rolling leaf sawflies
What are rose rolling leaf sawflies?
Rose rolling leaf sawflies often just referred to as rose sawfly are the same kind of insects as ant and bees. The adults have wings and look like flies, while the young look like caterpillars which are what do all the damage literally overnight. They make an appearance in spring and early summer when the female sawflies lay their eggs in the young rose leaves. The caterpillars hatch from the eggs and start feeding on your plant.
How to spot rose rolling leaf sawflies
When the female sawfly lays her eggs, she secretes a chemical into the leaf that causes it to curl up. That’s the signature sign that your plant has this problem. The edges of the leaves curl inwards and downwards, and the leaves end up as tubes.
Even after the caterpillar has finished eating in the leaf, the leaf stays in this shape for the rest of the growing season thats is the ones they have not totally stripped.
What to do
The rose rolling leaf sawflies are a part of the garden eco-system and generally not fatal. Most rose bushes can handle the loss of a few leaves. However, if you do get a large infestation of these insects, they may affect too many leaves for the plant to sustain itself in a healthy manner. They can devastate a whole rose in serous infestations so there not to be overlooked.
Pick off the affected leaves while the caterpillar is inside the rolled tube.
That’s it. A lot of pesticides don’t have any effect on this insect but a couple of sprays do if you can find them. Look for one such as Ultra-strong Bug Spray by Green heaven that is labelled as effective against sawfly.
What are rose leafhoppers?
Yet another sap-sucking insect is the rose leafhopper. With over 180 species, these bugs can fly or jump small distances when disturbed. They don’t cause noticeable damage to plants.
These insects are about 4mm long and pale yellow in colour. They sit with their wings folded away, leaving them quick to jump or fly.
How to spot rose leafhoppers
Look for a leaves that have a pale mottling on the upper surface. Over the growing period, the leaves may start to look bleached out.
If you have a large infestation of leafhoppers, the leaves they infest may turn brown and fall off.
What to do
Although they do suck the sap from the rose bush’s leaves, it rarely affects the health of the plant. Encourage the leafhoppers predators, including ladybirds/bugs (you can buy these) and ground beetles.
If you want to spray them with something, try a natural organic spray such as pyrethrum oil or neem plant oil.
Rose black spot
What is rose black spot?
Rose black spot is the most serious of rose diseases and probably the easiest to identify correctly. It’s a fungal disease that greatly reduces the plant’s strength. It infects the leaves and you can spot the disease from spring onwards. Rose growers breed resistance to rose black spot into cultivars but, unfortunately, new strains of the disease come up to overcome this so no rose is 100% resistant to Blackspot. The good news is that is never really fatal, it just looks very unattractive.
How to spot rose black spot
Thankfully, it’s easy to spot rose black spot. You notice a rapidly growing purple or black spot on the upper surface of the leaf. You may also see strands of the fungus there. There may be a yellow halo around the spot. The leaves usually drop to the ground before its fully infected.
Sometimes the spots remain small or the leaf doesn’t drop. There may also be lesions (scabs) on branches of the tree.
A severe infection of rose black spot can result in most of the leaves falling from the bush although its never really fatal.
What to do
First of all, remove all infected leaves, including those that have fallen to the ground. Continually disinfect your gardening gloves and cutting tools when doing this as you don’t want to spread this fungal disease. In spring, prune away all the branches with scabs on them before the new growth starts.
Be aware that this procedure has limited use as the fungal spores blow in on windy rain from elsewhere but its a good place to start.
Then look for a fungicide that’s marked as being for the control of black spots on roses, there are plenty of them, but I prefer Rose Clear and have used it for years successfully. I think the key to controlling blackspot and other diseases for that matter is spraying your roses in spring just as the leaves open before the disease is even showing. I find that this process helps prevents the disease in the first place or at least slow its spread down significantly. This will also help prevent powdery mildew which I talk about next.
Rose powdery mildew
What is rose powdery mildew?
Powdery mildew is a common disease for just about every plant in your garden, this is another consistent battle where prevention is key. And roses are no exception. It’s one of those diseases that doesn’t look too great but won’t cause severe damage to your plant.
I have a whole guide about it here – Powdery Mildew – How to control and prevent. Please read it for information about the disease and how to treat it. In a nut shell, remove as many affected leaves as possible and pray with a fungicide labelled for mildew. Spray roses in the spring before the disease sets in to help prevent it and try and have good airflow around your roses and avoid getting water on the leave when watering them.
What is rose rust?
Appearing in spring and summer, rose rust is another fungal disease, probably the most common after black spot on roses. But this one is specific to roses, so it won’t spread to any other type of plant in your garden such as fuchsia’s the rest they get is a different once.
Many modern rose cultivars are resistant to this disease so you may never see it in your rose bed but its still common place. But even if you do, rose rust is the least serious of rose diseases.
How to spot rose rust
As its name suggests, rose rust looks like, well, rusty spots on your rose leaves. You find orange or black boils on the lower side of the leaves, opposite yellow spots on the upper surface. The orange pustules also appear on the stems which become distorted. In late summer, the orange pustules turn black. And the infected leaves may fall off.
What to do
Snip off any infected leaves and stems (sterilised cutters, please). Do this in spring before the spores spread. Collect any infected fallen leaves throughout the summer but particularly in autumn.
As a last resort, look for a fungicide that’s labelled for controlling rose rust. Again, by spraying my roses in spring I’m often able to control it.
Botrytis blight and flower balling
What are botrytis blight and flower balling?
While flower balling is a disorder of roses related to the weather, it can lead to botrytis blight. I have an article about this with information on what to look for and what to do. Visit Why are my roses turning brown before they open?
What is root rot?
Root rot is another common fungal disease for many plants. It’s usually a result of over-watering the plant. However, under-watering your plant can also result in this disease if soil becomes water-logged. Excess moisture in soil creates a thriving environment for root rot.
There’s a whole article on what root rot is, how to treat it and how to avoid it. Check out Phytophthora Root Rot – prevention and treatment
What is rose dieback?
Rose dieback isn’t a disease as such. Dieback is when part of your rose plant is deteriorating, even dying. It’s caused by anything that stresses out the rose tree, including the weather, poor care, bad environment and diseases. Roots, branches, stems and new shoots that are in dieback are vulnerable to being invaded by fungal diseases. Dieback can happen at any time of the year.
How to recognise dieback
If part of your rose bush is turning brown, that’s usually indicative of dieback. Whole branches of leaves falling off, roots and stems that are black and squishy, frost-bitten tips of young foliage and withered flowers are all signs that your rose plant has experienced stress.
What to do
Remove all dead and damaged parts of your rose plant as soon as you notice them. Sterilise your sharp cutters frequently to avoid spreading any disease. See the article How and when to prune roses for details.
Then check that you’re giving the rose tree the correct care and attention. How to grow and care for roses and How to grow and care for roses in pots are two articles with all the information you need.
Then re-read the rest of this article to pin down any pest and disease that may be causing the stress that lead to the dieback.