Diplocarpon

Diplocarpon is a genus of plant-pathogenic fungi, best known for causing leaf spot diseases on ornamental and fruit plants. The most prominent species is Diplocarpon rosae, the causal agent of black spot disease on roses, with other Diplocarpon species described on various hosts.

Symptoms of Diplocarpon infections typically appear as round to irregular black to dark brown spots on leaves, often with yellow halos. Spots may coalesce, leading to extensive leaf chlorosis, premature defoliation, and reduced vigor and flowering. In roses, black spot is particularly noticeable in cool, wet conditions and can spread rapidly during damp springs and autumns.

Life cycle and biology: Diplocarpon species overwinters in infected plant debris, such as fallen leaves. In favorable spring weather, spores are produced on litter or infected tissue and spread mainly by rain splash. Leaf wetness and suitable temperatures promote infection. The fungus can reproduce sexually, forming pseudothecia that produce ascospores, and asexually, producing conidia in conidiomata; both spore types can initiate new infections, allowing several disease cycles within a growing season.

Management: Effective control relies on cultural practices and, when necessary, chemical protection. Sanitation to remove and destroy infected leaves and debris reduces inoculum. Improving air circulation through pruning and avoiding overhead irrigation helps keep leaves dry. When appropriate, fungicides registered for leaf spot diseases can be applied according to local guidelines and resistance management principles. Some cultivars show partial resistance, contributing to lower disease pressure.

Distribution: Diplocarpon rosae occurs worldwide in temperate regions and is a major concern for roses in gardens and nurseries. Other Diplocarpon species occur on different host plants, reflecting the genus’s broader plant-pathogenic roles.