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Marssonina rosae
Leaf spots are easily seen and may be serious on roses, which is very commonly attacked by black spot. Spores are easily spread by water splash and infections take hold when the water remains on the leaf for about 6-7 hours. Areas with high summer rainfall and high humidity usually have the highest incidence of black spot.
Circular black spots on the leaves which are fringed with yellow margins. The spots are black and can also appear on the stems. The leaves will fall prematurely and if left unchecked can lead to defoliation of the plant.
Treatment of the disease is year round as the fungus overwinters on stems and leaf litter. All diseased leaves should be raked up and disposed of. Diseased stems need to be pruned back to healthy wood. Spray roses with Yates Lime Sulfur Concentrate in winter and start an early preventative spray program at the beginning of spring once foliage emerges.
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