What’s Eating My Rose Leaves?

roseslug sawfly damage on rose

Rose slug sawfly damage on rose. Photo: UME/Ask an Expert

Q: My rose leaves have white spots and holes in them. What causes this and how do I treat it? Is there a natural remedy that does not involve powerful chemicals?

Answer: It looks like your rose has symptoms of sawfly damage. Check the undersides of the leaves and look for tiny green larvae that look like caterpillars. These are the juvenile stage of an insect called rose slug sawfly.

Rose slug sawflies are neither slugs nor flies. They belong to the same order of insects as wasps, bees, and ants (Hymenoptera). Adult female sawflies use their unique ovipositor (egg-laying part) to saw a small slit in a leaf or stem where they lay their eggs. When the eggs hatch, the larvae feed on the leaf surfaces and cause an etched appearance. Some rose slug larvae chew through leaves entirely. Damaged foliage turns brown and curls up as the season progresses.

bristly roseslug on rose leaf

Bristly rose slug (Cladius difformis). Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

bristly roseslug sawfly adult

Bristly rose slug (Cladius difformis), adult stage. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

In Maryland, there are three species of rose slug sawflies that cause damage to roses: the bristly rose slug sawfly, the rose slug sawfly, and the curled rose sawfly. Most of the feeding activity on roses in Maryland is seen in May and June, but sawfly larvae can continue to be active until fall. Other insects, such as Japanese beetles, also cause chewing damage on rose foliage (typically in June-July).

rose-brown-leaves

Browning and leaf curling from rose slug sawfly damage. Photo: UME/ Ask an Expert

The best way to manage rose slug sawflies without chemicals is to monitor your plant(s) for damage symptoms and manually remove any larvae (squish them or toss them). Insecticidal soap, horticultural oil, and spinosad work well against these sawflies. These products are environmentally friendly insecticides listed by the Organic Materials Review Institute (OMRI). As with any pesticide, read and follow the label instructions carefully. Avoid sprays when your roses are in bloom, to protect pollinators and other beneficial insects.

Predatory insects and parasitoids help regulate sawfly populations naturally. Adding more flowering plant diversity to your landscape will provide food and habitat for beneficial insects that in turn will help reduce pest problems.

Additional Resources

Rose Slugs on Shrubs | UME Home & Garden Information Center

Rosie Defoliators | Bug of the Week, University of Maryland, Department of Entomology

Rose Insects & Related Pests | Clemson Cooperative Extension

Sawflies | University of Wisconsin-Madison

By Christa K. Carignan, Maryland Certified Professional Horticulturist, Coordinator, University of Maryland Extension Home & Garden Information Center

Have a plant or insect question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.

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