Several species of slug sawflies injure rose leaves. Their slug-like bodies and feeding styles produce characteristic window-pane damage on leaves. These wasp larvae usually feed from the underside of the leaf, leaving a thin layer of pale green epidermis (Figure 1). Feeding sites soon dry and disappear so only irregular holes remain. Damage can be extensive. The bristly rose slug caterpillar is the most nefarious of the group because it has multiple generations during the summer; other species that attack roses have only one or two generations.
Check upper and lower leaf surfaces of rose foliage regularly to detect infestations as they begin. Egg laying and hatch continues over an extended period, so damage control is not limited to a week or two in early spring.
- Remove infested leaves.
- Knock small larvae off of plants with a strong stream of water
- Crush small larvae as they are found.
- Check the label of insecticides registered for pests of roses and other flowers to see if sawflies are listed. Read and follow instructions to protect pollinators.
By Lee Townsend, Extension Entomologist