Diagnosing Problems on Thérèse Bugnet Roses

Three Issues on a Mature Shrub Rose

A 4-year-old Thérèse Bugnet showing bud failure, black spots on canes, and bulbous leaf growths likely has three separate problems.

1. Leaf Galls (Bulbous Growths)

These are caused by tiny gall-making insects (often cynipid wasps or midges) that disrupt normal leaf development. They are cosmetic and don't harm the plant's health. Simply prune off affected leaves and dispose of them (burn or trash) to reduce future populations.

2. Rose Midge Damage

Tiny midge larvae feed inside flower buds, causing them to wither, brown, and fail to open. Apply a rose insecticide labeled for midge control according to directions, targeting the base of buds early in the season.

3. Cane Black Spot (Fungal Disease)

Black lesions on canes indicate the fungal disease black spot (Diplocarpon rosae), which overwinters on canes. Use a rose fungicide specifically for black spot. Combination insecticide/fungicide sprays (like Bayer Advanced) simplify treatment.

Integrated Management

• Clean up all fallen leaves and debris in winter.
• Prune out infected canes well below visible damage.
• Apply preventive sprays early in the growing season.
• Ensure good air circulation through proper spacing.