Rose diseases

Black Spot

Black spot is one of the most common and persistent diseases affecting roses. It’s caused by a fungus that produces black, irregular-edged spots on the leaves, which can spread quickly and lead to yellowing and premature leaf drop. The problem tends to worsen in damp conditions, so it’s advisable to choose disease-resistant varieties where possible. However, as with many living organisms, the fungus can mutate over time, potentially affecting even the most resistant roses and becoming less responsive to fungicide treatments.

The best approach is to act swiftly at the first sign of infection. Remove and destroy any affected leaves immediately—do not compost them, as this can spread the disease. Collect and dispose of any fallen leaves from around the base of the plant. If you choose to use a fungicide, begin treatment early in the season and follow the instructions carefully, reapplying as needed to keep the infection under control.

While a mild case of black spot won’t usually kill a rose, a severe infestation can significantly weaken the plant, so it’s important to manage it as effectively as possible.

Powdery Mildew

Occasionally, when roses arrive from the nursery, you may notice white patches on the leaves but not on the buds or stems. This is usually just a residue left behind by evaporated water from overhead irrigation and is nothing to worry about—it can be gently wiped off or will wash away with the next rainfall.

However, if your rose develops grey patches  beneath the buds or on young stems, it may have contracted  powdery mildew. This fungal disease thrives in conditions where the soil is dry but the air is humid. It typically appears as a powdery grey coating on leaves, buds, and tender stems.

To prevent and control powdery mildew, ensure the soil is kept well-watered and apply a mulch of organic matter to retain moisture. Prune the centre of the plant to improve air circulation, and consider using a sulphur-based spray to limit the spread. As always, remove and destroy any fallen or infected leaves to reduce the risk of reinfection.

Rose Rust

Rose rust can be identified by the presence of orange spores on the underside of leaves and yellow-orange spots on the upper surface. It usually appears from midsummer onwards and can cause premature leaf drop, reducing the plant’s overall vigour.

At the first sign of rust, prune out affected areas and remove any fallen leaves. If necessary, apply a fungicide specifically recommended for treating rose rust. Prompt action will help to minimise damage and keep your rose healthy throughout the season.