How to Keep Those Pesky Green Bugs—aka Sawfly Larvae—Off Your Roses

If you've noticed little green worms on the underside of your rose bush's leaves, it's time to take some action. Commonly known as rose slugs, these caterpillar-like creatures are the larvae of a sawfly (a small, non-stinging wasp relative). Rose slugs won't hurt you and they won't kill your plants, but you may want to get rid of them ASAP because they will quickly eat holes in your rose foliage. The good news is that there are a few easy ways to get them under control without having to reach for a pesticide. Here's how to get rid of rose slugs in your garden.

What Is a Rose Slug?

Rose slugs look like caterpillars or even miniature slugs, hence their name. But in actuality, a rose slug is neither a true slug nor a caterpillar (which becomes a moth or butterfly). It's simply a larva of the rose sawfly. Velvety and yellow-green in color, rose slugs can get up to half an inch long.

Signs of Rose Sawfly Damage

The sawfly larvae will appear on roses in late spring and begin eating the soft, green tissue of leaves. The remaining veins of the leaf that they don't eat will turn brown and crisp. The damaged foliage will have a window-pane or skeletonized appearance. Generally, rose slugs just make plants look bad, but most roses will just grow new leaves once the pests are gone. Sometimes, heavier infestations can weaken your rose plant enough that it's more vulnerable to other insects and plant diseases.

Check Plants for Signs of Infestation

The key to effective rose sawfly control is to find the larvae while they are still small and before the damage becomes severe. Start looking for sawfly larvae on the lower surfaces of your rose leaves in mid-spring. There is no need to treat the rose foliage after the larvae have finished eating and are no longer on the plants. The larvae only stick around for about a month before they make their cocoons.

How to Treat Sawfly on Roses

If you have a small number of rose slugs on just a few plants, the best approach would be to hand-pick them off and drop them in a cup of soapy water. You can also use a forceful spray of water out of a garden hose, which will knock off and destroy many of the larvae. Be sure to spray the water at both the upper and undersides of leaves.

You can also use an insecticidal soap ($7, The Home Depot) or insecticide-containing neem oil ($11, The Home Depot). These products are derived from natural chemicals, as opposed to synthetic pesticides, which can be more toxic to non-target species. However, all pesticides should be used according to label instructions.