Aptly named black spot is a fungus that causes dark spotting on rose leaves and stems. Eventually, leaves turn yellow and drop off before autumn. Spores overwinter on the fallen leaves and re-infect the plant in spring when new foliage appears. Plants can be weakened by recurrent attacks, especially if they occur early in the season.
Symptoms of rose black spot
Leaves are disfigured by poorly defined purple-brownish-black blotches. The leaves then turn yellow and fall. Stems might also be affected.
Find rose black spot on
Organic methods for dealing with rose black spot
Pick up and destroy fallen leaves. When pruning, cut out any stems with black spot on. In late-winter, spread a thick layer of mulch around the base of the affected plant to prevent rain splashing soil-borne spores on to new spring growth. Grow rose varieties that are resistant to black spot – these are suggested in the catalogues of specialist rose growers.
Chemical methods for dealing with rose black spot
Spray against black spot with a fungicide. Follow the instructions, treating the new foliage in early spring, with further sprayings at regular intervals through the season.