When to Spray Roses With Spinosad for Sawfly

The Culprit

• Sawflies are small wasps that lay eggs on rose foliage. These in turn hatch and become the larvae. There are three main types of sawfly. The rose slug, bristly rose slug and curled rose sawfly are all damaging chewing pests that eat rose leaves. The larvae are only 1/2 inch long and may be smooth and slimy or prickly and hairy. Rose slugs only have one generation per year but the others have two or more. This can cause serious damage to the rosebush.

Damage

• Rose slugs eat the upper leaf surface and leave the lower layer and the veins. The damage is called skeletonization because it just leaves a skeleton of leaf material behind. The curled rose sawfly is the most damaging because it also pupates at the center of twigs and invites fungal infections. Rose slugs will also feed on the flower buds and diminish flowering. Rose slugs are green and difficult to spot but their feeding can cause rapid leaf loss. A pesticide such as spinosad is safe to use and will cause no harm to beneficial insects if applied as a preventive.

Spinosad

• Sawfly larva may be handpicked or hosed off with water, but a safe and nontoxic pesticide is also available. Spinosad is an organic spray that is composed of two soil microbes. It is broad spectrum to insects but has no effects on mammals, so it is safe for use around your pets and children. It is only toxic to insects if they contact it while still wet or ingest it, so it is ideal for leaf-chewing insects. It also means that flying insects such as bees are safe and the product has few ill effects on other beneficial insects.

Timing

• May is the time to begin looking for sawfly larvae. Depending on your zone, they may hatch a little earlier so start in April in warm-season climates. From May through the end of June, you should spray spinosad on the leaves. The spray has to go on the upper and lower parts of the leaves to contact all the slugs. Spinosad is a relatively new insecticide but is safe to use as a preventive if you wish to spray it in April or May. It is also effective against many of the other common rose pests.