Black spot is a very common fungus disease of roses in Vermont.
Infected leaves eventually yellow and drop prematurely. Severe infection may cause some canes to become completely defoliated, making the canes more susceptible to winter damage. The fungus that causes blackspot, Diplocarpon rosae , thrives under wet conditions. Spores from infected fallen leaves from the previous season are splashed onto new emerging foliage in the spring. If temperatures are warm following infection, symptoms may become visible in three days.