Red Spots on Yellow Rose Petals: Cercospora or Black Spot?

Small maroon-to-purple oval spots with tan centers on yellow rose petals/leaves indicate Cercospora leaf spot, a fungal disease distinct from classic black spot. It thrives in humid conditions and affects groundcover roses heavily. Both diseases respond to the same fungicides (e.g., Ortho Rose Pride, sulfur, or neem oil).

Management

• Spray at first sign, repeat every 7–10 days.
• Never spray in hot sun (above 85°F) to avoid burn.
• Remove infected leaves; clean up fall debris.
• Improve air circulation with pruning.

Winter dieback to ground in Winnipeg suggests marginal hardiness—mound soil 12 inches over crown next winter.