–by Raymond Cloyd
There are at least two species of sawflies that attack roses during this time of year; the rose slug (Endelomyia aethiops) and bristly rose slug (Cladius difformis). Rose slugs are the immature (larval) stage of sawflies, which are black to yellow-colored wasps.
Rose sawfly females make pockets or slits along the edges of rose leaves using their saw-like ovipositor (egg-laying devise), and insert individual eggs. Eggs hatch into larvae that look-like a slug. Larvae are 1.2 cm in length when fully grown and yellow-green in color, with an orange head (Figure 1). The larvae eventually fall on the soil surface to
pupate. Rose slugs overwinter as pupae in earthen cells created by the larvae. There is usually one generation per year in Kansas. Bristly rose slug larvae are pale-green in color and 1.5 to nearly 2.0 cm long. The body is covered with numerous bristle-like hairs (Figure 2). There is generally one generation per year in Kansas.
Rose slug larvae feed on the underside of the leaf resulting in the leaves having a skeletonized appearance (Figure 3), eventually they create notches or holes on the leaf margins. Bristly rose slug larvae feed on the leaf undersides and also cause leaves to appear skeletonized (Figure 4). However, the larvae may chew larger holes than the rose slug.
Small infestations of either the rose sawfly or bristly rose slug can be removed by hand and subsequently placed into a container of soapy water. A forceful water spray will quickly dislodge sawfly larvae from rose plants; consequently, sawfly larvae are not able to crawl back onto rose plants. A number of contact insecticides (various active ingredients) may be effective in suppressing populations of both sawflies. However, the bacterium, Bacillus thuringiensis subsp. kurstaki (sold as Dipel or Thuricide) will have no activity on sawflies as this compound only works on caterpillars.
