Blackspot is one of the most common and serious fungal diseases on rose plantings throughout Kansas. The leafspot lesions are roughly circular and have distinctive irregular, feathery margins. Individual leaves may develop multiple leafspots. At the beginning of the growing season, blackspot will start to develop on the lower leaves and will move upward through the plant as the season progresses. Infected foliage eventually turns yellow and falls off the plant.
Heavy infections can seriously defoliate a plant.
Infected canes develop raised, purplish-red spots or blotches, which eventually blacken and appear blistered. This means the disease is primarily active in late spring or early fall and whenever warm, wet weather occurs. Blackspot primarily overwinters on infected leaf litter beneath the rose bushes. In the spring, fungal spores are windblown or splashed up on to newly emerging leaves on the lower portion of the plant. As the season progresses, spores from newly infected foliage are splashed or blown upward to infect more leaves.