Tiny White Holes in Knockout Rose Leaves: Rose Slugs (Sawfly Larvae)

A gardener asked what causes Knockout rose leaves to become riddled with small white holes.

The Culprit: Rose Slugs (Sawfly Larvae)

Despite the name, these are not slugs but the larvae of primitive wasps (sawflies). Females lay eggs in leaf margins. Larvae hatch and feed on leaf undersides, creating "windowpane" damage—transparent tissue that turns white/brown and falls out, leaving holes.

Life Cycle

• Larvae feed → drop to soil → pupate in cocoons → emerge as adult sawflies.
• Multiple generations per year.

Effective Control

Most insecticides fail—larvae must be smothered. Use:

• Insecticidal soap (Safer's) – thorough coverage, both leaf sides.
• Neem oil or horticultural oil – smothers larvae.
• Spray base of plant and soil – pupae and adults hide there.

Early detection is key. Small larvae = small holes. Large larvae = skeletonized leaves. Treat at first sign.