“Bleached” leaves are appearing on landscape roses in southwest Ohio. Unfortunately, I only need to walk to the end of my driveway to see the damage on ‘Knock Out’ roses.
The culprit behind the damage is a sawfly (family Tenthredinidae, order Hymenoptera) called the Roseslug (Endelomyia aethiops (formerly Caliroa aethiops) The non-native sawfly is sometimes called the European Roseslug, denoting its place of origin.
The roseslug sawfly larvae can grow to around 1/2” long. Their coloration allows them to blend with their background to some degree making them difficult to detect, particularly if they’re feeding on the lower leaf surface. Although they have “slug” in their common name, they don’t share the slug-like body plan of the true “slug sawflies” and the larvae don’t cover themselves in slime.
The roseslug larvae feed on both the upper and lower leaf surfaces. They consume all of the leaf tissue except the leaf veins and the epidermis on the opposite leaf surface. The intact leaf epidermis may turn white, causing leaves to appear bleached, or leading to a subtle “windowpane” effect.
The roseslug sawfly has one generation per season, and based on the size of the larvae that I photographed, they appear to be nearing the end of their development. They will eventually drop to the ground, where they pupate and remain until adults emerge next spring.
Most of the damage has already occurred for this season, and although it’s currently very evident, the damage will eventually fade as it’s covered by new foliage. Thus, there is no justification to spray for this early-season pest.
