Skeletonized Rose Leaves? It's Likely Rose Slugs, Not Caterpillars

Knockout and miniature roses showed colorless round/oval patches on leaf undersides that turned into holes, skeletonizing the leaves (veins left intact). Damage was only in leaf centers, not edges. A local expert suggested caterpillars and Bacillus thuringiensis (Bt).

Rose Slugs (Sawfly Larvae)

The damage is classic rose slug feeding: they eat the soft tissue between veins from the underside, leaving a lace-like skeleton. They drop to the soil to pupate and repeat the cycle. Bt does not work on sawfly larvae—it only affects caterpillars (Lepidoptera).

Effective Control

Remove and destroy all infested leaves. Spray with horticultural oil or neem oil, covering leaf undersides thoroughly. Also spray the soil around the base. These organic options smother the larvae and disrupt the life cycle.