Rose black spot is a fungal disease of roses, the most common, serious and devastating that damages these flowers. The symptoms of this disease can vary from rose to rose and from year to year. It usually starts as black or dark purplish spots or blotches on the leaves, which rapidly spread across the leaf. These are usually followed by the leaf turning yellow around the spots/blotches.
The affected leaves usually drop prematurely from the plant, and badly affected roses can shed nearly all their leaves. Attacks of black spot disease year after year will seriously weaken the plant, causing severe dieback and greatly reduced flowering performance. The fungus – Diplocarpon Rosae – is very common here in the UK, especially in late summer, due to the warm, yet wet, weather conditions. Harry Lloyd, gardening expert at waste removal company HIPPO, claimed that the best form of prevention is to avoid wetting the leaves and flowers of the plant.
He said: “My top tip for preventing black spots on rose leaves is to focus on keeping the leaves and foliage dry. The number one mistake people make with roses is overwatering, especially at this time of year – and this excess moisture creates a breeding ground for fungal disease.
“Newly planted roses need much more regular watering than when they’re fully established; however, the mistake many people make is increasing the amount of watering over time as the plant grows, rather than actually decreasing it.”
On top of this, towards the end of summer, as the air becomes more humid and we start to get more rainfall, rose bushes will naturally absorb far more moisture, further reducing the need for such frequent watering.
Harry pointed out that there’s no hard and fast rule for how often you should water your roses, but just pay attention to them and respond accordingly.
There are a few questions gardeners need to ask themselves before watering roses. Are the leaves turning yellow, brown or starting to wilt? Do the stems feel mushy and squishy? And perhaps the most obvious – are the few inches of surface soil beneath the plant damp? If so, it doesn’t need watering yet.
Also, when you do water your roses, “only water the base of the plant”, being careful to keep the leaves dry.
Another helpful way of keeping your roses clean and dry to prevent black spots is by ensuring the plant has “plenty of space to allow for better air circulation”.
A cramped, crowded rose bush is a “magnet for black spot” because the humid, stagnant conditions between the leaves and stems create the ideal environment for fungal spores to germinate.
When pruning your roses, Harry insisted: “Aim for a wine glass-like shape. This allows for free airflow throughout the plant, further helping to regulate moisture levels.”
