Lacy Leaves on Knockout Roses: Sawfly (Rose Slug) Damage

St. Louis area Knockout rose (1.5 years old) developed lacy, skeletonized leaves last summer. New growth shows same damage this year. Neighbor's roses affected too.

Pest: Rose Sawfly / Rose Slug (Endelomyia aethiops)

Not a true slug—sawfly larvae feed on leaf undersides, eating tissue between veins. Transparent "windows" appear first, then holes, then complete skeletonization. Multiple generations per year.

Identification

• Check leaf undersides for tiny, greenish-brown, caterpillar-like larvae (often curled)
• Early instars: 1-2mm, translucent green
• Mature: ~1/2 inch, light brown head
• Adult: Small, fly-like wasp (rarely seen)

Control

Any rose insecticide works (Ortho RosePride, spinosad, neem oil) IF applied to leaf undersides and around base where larvae drop to pupate. Systemic products (Bonide Systemic Rose Care) provide longer protection.

Good News

Roses produce 3+ leaf sets per season. Once controlled, new growth emerges clean. Plants rarely die—just look terrible temporarily. Neighbor coordination helps since adults fly between yards.

Prevention

• Scout weekly from May onward
• Remove leaf litter in fall (pupation site)
• Encourage birds—natural predators