Rose black spot is an important fungal disease of roses that is most active towards the end of spring. The fungus overwinters in infected plant debris from the previous season.
The fungus causes black spots to form on the upper surfaces of leaves. Defoliation can occur in heavily infected plants. Rain, overhead irrigation, and any other water-splashing sources trigger spores from infected plant debris.
Rose black spot tolerates a broad range of weather conditions, thus it allows symptoms to develop throughout the season.
Plant resistant varieties: Planting roses that are resistant to black is the most effective strategy for prevention.
Sanitation: Dispose of diseased leaves and other plant debris that fell off. Don’t use infected plants parts in composts.
The following are generic names of fungicides used in one or more parts of the world: azoxystrobin, trifloxystrobin, Myclobutanil, penconazole, pyraclostrobin, and kresoxim-methyl.
*Names marked in red are considered to be highly poisonous to beneficial insects.
*Names marked in green are considered to be organic and IPM (integrated pest management) compatible.