Which common disease is known to affect roses in nurseries?

The common disease known to affect roses in nurseries is black spot, which is caused by the fungus Diplocarpon rosae. This fungal infection is particularly problematic for roses because it leads to distinctive black spots on the leaves, which can result in early leaf drop and overall decline in the health of the plant. This can affect the aesthetic appeal and vigor of the rose plants in a nursery setting, leading to significant economic losses for growers.

Powdery mildew is a fungal disease that also affects roses, but its distinguishing feature is a white, powdery coating on leaves, rather than the black spots characteristic of black spot. While both diseases can occur simultaneously and are important to manage, the specific question asks for the common disease frequently associated with roses in nurseries, making black spot the more prominent choice in this context.

Rust and downy mildew are diseases that can affect various plants but are not as commonly linked to roses specifically in nursery situations. Rust is usually associated with a different set of plant families, while downy mildew tends to affect foliage differently and is less common in rose cultivars. Therefore, black spot stands out as the most significant disease impacting roses in nursery environments.