Answer: Based on your description, the plant may be affected by a foliar problem such as black spot. This is a fungal infection and as with other foliage problems, wet weather can encourage it where a relatively dry season will discourage it.
Control measures for these types of foliage problems include planting the rose in a location with full sun and good air circulation plus pruning to open the interior of the bush to air and sunlight. It is important to remove and destroy all of the hips and foliage at the end of the season, even picking the plant clean in winter if needed, to limit reinfection from year to year. For the same reason, replace or add a clean layer of mulch each winter after you remove the foliage so that spores will not splash back up onto the plant. During the growing season, prompt removal of infected foliage early in the season can help slow the spread of the problem. Finally, avoid wetting the foliage when watering. Hansa is somewhat resistant to black spot so I would expect prompt action and some ongoing vigilance should be sufficient to keep it under control for you.
Q&A Library Searching Tips