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The leaves on your roses are curling, most probably due to a pest or disease, with the most likely reason being a pest called Rose sawfly, which I discuss further down in more detail. However, it could be powdery mildew which is easy to identify by the white fine coating, which you usually notice first.
Another possible reason, especially if you grow roses in pots which I talked about here. It might be as simple as you’re under-watering your plant.
Read on to determine your plant’s problem with curling leaves and what to do about it.
Rose powdery mildew
Powdery mildew is one of the more common fungal rose diseases. In fact, it’s a common disease for many plants in your garden, and I covered it many times on this site for various plants. The spores that produce this disease are air-borne, so avoiding them is difficult. The leaves of your rose may turn yellow, purple or red color on the upper and/or lower surface. The leaves may also curl. You may also notice powdery mildew on the flower buds of roses too.
I have an extensive section I have written on this disease and what to do about it in my Rose pests and diseases guide. In a nutshell, I recommend removing as many infected leaves as soon as possible and burning them, don’t put them in your compost bin as this can spread to other plants.
Then spray with a fungicide, ideally labelled for use on roses and reapply after two weeks. This disease is best prevented, and I have managed to achieve this by simply spraying the leaves in spring as soon as they open with a fungicide. I have found this also helps prevent other diseases, including rose black spot and Rust.
Botrytis blight is another fungal disease that causes rose foliage to curl up, and this is a much more serious disease. If flower balling occurs, and the flower buds dry up, then a suitable environment for this disease occurs.
Please see the section on Flower balling and botrytis blight in my guide Why are my roses turning brown before they open? For much more information about this common disease. Botrytis blight usually shows after flower balling, which is a problem when fully developed buds don’t open and dry out in summer, and it usually happens in cool wet weather. I recommend pruning back affected parts of the plant and treating them with a natural fungicide such as pyrethrum oil or neem plant oil.
One pest that results in the leaves on your roses curling is the rose leaf rolling sawfly. These insects are in the same group as bees and ants.
While the caterpillars of this pest eat the leaves of your rose, the female sawflies secrete a substance that causes the leaves to roll up tightly with the eggs inside. This is usually the first sign of a rose sawfly problem before the caterpillars strip the leaves off the roses which they do within a day or two.
If you’ve checked out your rose tree for pests and diseases and found nothing, the curled leaf problem could be due to you under-watering your plant. This could especially be the case if the leaves are also yellow and a bit crispy. This is more common with roses grown in pots as they have limited soil and can become root bound, which means they cant retain moisture in the soil.
Not giving the plant enough water results in the leaves curling up to preserve the water they do receive. Leaves lose water by transpiration (evaporation), and conserving water is the plant’s way to stay healthy.
You may not be getting enough water to your plant even if you’re watering it well.
Also consider if your rose has actually been overwatered?
In other guides in the Rose series, I emphasise the importance of drainage holes in the bottom of the pot if you’ve planted your rose in one, plus the importance of not having your rose sit in water-logged soil in the ground.
You may have the opposite problem in which the water is draining away too fast before the roots can take it up. If this is the case, add more organic material to the soil or compost to help retain the water. Bark also helps to keep the water around for a while.