Rose Slug (Sawfly) Damage: Identification and Control

Yellow knockout rose leaves with holes, no visible bugs. Owner seeks cause and treatment.

Diagnosis: Rose Slugs (Sawfly Larvae)

Rose slugs feed on leaf undersides, scraping tissue between veins. This creates "windowpanes" that dry and become holes. Heavily damaged leaves yellow and drop. Larvae are green, caterpillar-like, often invisible on leaf undersides.

Control Strategy

1. Spray undersides: Use rose spray labeled for sawflies/rose slugs.
2. Treat soil base: Larvae drop to ground to pupate—spray around plant base.
3. Early detection: Scout weekly in spring; one generation often precedes visible damage.
4. Annual vigilance: They return yearly—early control prevents major damage.

This is not a disease—no fungicide needed. Insecticidal soap, spinosad, or neem oil work well if applied to leaf undersides.