Preventing rose disease


Tidy up any fallen rose leaves now, especially if they look spotty because this is almost certainly a result of a fungal disease called black spot (Diplocarpon rosae). This debilitating disease leads to poor flowering and defoliation, but not all roses are susceptible. Rugosas, gallicas, ramblers, most modern floribundas and all groundcover roses have a resistance to blackspot either inherited naturally or bred into them. Even susceptible roses, mainly old-fashioned ones, will resist if well pruned and fed.

Once you have black spot, it tends to return year after year because the fallen foliage under your roses transfers the spores to the soil. They linger and when it rains the spores splash back onto the rose, creating a cycle of infection. However black spot, like all fungal diseases, is more of a problem in warm, damp summers.

Black spot spores will overwinter in fissures or cracks of rose stems. However it’s much less likely to strike if your rose is well-fed and well-pruned. When pruning aim for an open shape, rather than a congested one, so that the air flows through the branches. Feed your roses as soon as spring arrives, using Vitax Q4 or J Arthur Bowers Rose Food. Both are high in potash, helping to produce tougher foliage and more flower buds. Another feed after the main flush of flower will also help. Avoid over-head watering of roses, as this also transfers spores. If you have to irrigate keep the water off the foliage.

One of the best ways to prevent blackspot is to create a carpet of herbaceous plants placed between rose foliage and soil surface. This acts as a barrier, preventing the spores from being splashed back up. The secret of success is choosing non-invasive plants that flatter your roses.