Rose Sawfly

We have received numerous inquiries about insects feeding on the leaves of rose plants. The insects are sawflies, and there are at least two species that attack roses this time of year: the rose slug, Endelomyia aethiops, and the bristly rose slug, Cladius difformis. Rose slugs are the immature or larval stage that eventually becomes a black to yellow-colored adult, which resembles a wasp. Rose sawfly females create openings or slits along the edges of rose leaves with their saw-like egg laying device (ovipositor) and insert eggs. Larvae emerge from the eggs and resemble small slugs. Larvae are approximately 1/2 of an inch long when full-grown and yellow-green, with an orange head.

Rose slug larvae feed on the underside of rose leaves, causing the leaves to appear skeletonized. The larvae create notches or holes on the leaf margins. Bristly rose slug larvae feed on the underside of rose leaves, causing leaves to appear skeletonized. However, the larvae create larger holes than the rose slug. Small infestations of either the rose sawfly or bristly rose slug can be dealt with by removing the larvae by hand and placing them into a container of soapy water. A high-pressure water spray will quickly dislodge sawfly larvae from rose plants, and they will not crawl back onto rose plants. There are several contact insecticides containing various active ingredients that are effective in managing populations of both sawflies. Sawflies are not caterpillars. Consequently, the bacterium, Bacillus thuringiensis subsp. kurstaki, which is the active ingredient in various products (e.g. Dipel^®), has no activity on sawflies because the insecticide is only effective against caterpillars.

 

Have questions? Contact our office where our Horticulture Extension Agent will assist you with questions.

Phone: (316) 321-9660

Email: callae@ksu.edu