Tiny Green Worms on Roses: How to Identify and Get Rid of Rose Slugs

Rose slugs, the tiny green worms found eating away at rose leaves, can quickly damage ornamental rose bushes. These little caterpillar-like pests are actually not caterpillars at all but are the larvae of sawflies. Learning to identify rose slugs and using integrated pest management techniques can help you protect your roses from extensive damage.

What Are Rose Slugs?

Rose slugs as the name suggests look like small slugs crawling on the leaves of rose bushes. However, they are not mollusks like regular slugs. Rose slugs are the larvae of a type of wasp called the rose sawfly. There are a few different species of sawflies that target roses, all in the genus Allantus.

The adult sawfly wasps lay their eggs on the underside of rose leaves in the spring. The eggs hatch into larvae that immediately start feeding on the leaf tissue, leaving behind the veins so the leaf looks like lace These green worms on roses grow to about half an inch long before forming cocoons and dropping to the ground to pupate

After 1-2 weeks, adult wasps emerge from the cocoons to mate and start the life cycle over again. There is usually one generation per year, occasionally two.

Signs of Rose Slug Damage

The first sign of rose slugs is holes in the leaves, typically starting on lower leaves first. Look on the underside of leaves and you will likely see the small green worms eating away. They feed for about 4 weeks before dropping to the ground.

Rose slug damage causes leaves to turn brown along the remaining veins, giving them a skeletonized appearance. Heavy infestations can significantly defoliate plants. Severe defoliation can weaken rose bushes, making them more susceptible to winter injury or disease.

Check susceptible rose varieties regularly starting in late spring when sawflies first become active. Targeted pest control measures work best when applied soon after eggs hatch and before larvae grow large.

How to Get Rid of Rose Slugs

Handpick and Prune

For light infestations on a few rose bushes, handpicking the larvae off plants can provide adequate control. Drop them in a bucket of soapy water which will kill them quickly. Also prune off any heavily damaged leaves and destroy them.

Strong Water Stream

Use a strong stream of water to knock larvae off plants. Focus on leaf undersides. The force of the water should be strong enough to kill many of them. Repeat daily until they are gone.

Insecticidal Soap

Insecticidal soap sprayed directly on larvae will kill them without harming beneficial insects. It works by penetrating and destroying the outer membranes of the worms. It may need multiple applications as new generations hatch.

Neem Oil

Neem oil is extracted from the neem tree and kills larvae upon contact. It also acts as a repellent against the adult wasps laying more eggs. Neem oil can be mixed with insecticidal soap for added effectiveness. Like soap, it may need reapplication.

Natural Predators

Encouraging natural predators like birds, lady beetles, lacewings, and parasitic wasps can help reduce rose slug populations. Avoid broad-spectrum insecticides that kill these beneficials. Plant a diversity of flowering plants to provide habitat and food sources.

Set up bird feeders, birdbaths, bird houses, and perches to attract insect-eating birds to your yard.

Diatomaceous Earth

Spreading diatomaceous earth (DE) on the soil around roses can help kill larvae as they drop down to pupate. The microscopic sharp edges of DE cut into the larvae’s bodies, causing them to dry out. Reapply DE after heavy rains.

Row Covers

Covering rose bushes with fine mesh fabric row covers can exclude sawflies from laying eggs on plants. Install covers in early spring before sawflies are active. Make sure plants have good airflow and ventilation. Remove covers to allow pollinators access during bloom.

Preventing Rose Slugs

• Start inspection rose bushes in late spring and treat early before damage becomes severe.

• Avoid excess fertilization which causes fast, tender new growth that sawflies prefer.

• Prune out any dead or damaged canes which can harbor overwintering sawfly larvae.

• Remove fallen leaves and debris around plants that provide protection for pupating larvae.

• Plant resistant rose varieties like rugosas which have tough leaves sawflies dislike.

• Rotate spots where roses are planted each year to prevent buildup of larvae in soil.

• Choose less susceptible species like knock-out, landscape, and groundcover roses.

By identifying signs of rose slugs early and taking prompt and thorough action, you can help protect your ornamental roses from these hungry little green worms. Combining multiple organic and natural control methods often provides the best protection.