Sawfly larvae
Caterpillar-like larvae that skeletonize or strip the leaves of roses, pines and fruit; Bt won't kill them.
What you'll see
- Leaves eaten down to a lacy skeleton or stripped to the midrib, often working in from the edges.
- Green, slug-like or caterpillar-like larvae, often in groups, under the leaves or along shoots.
- Count the stubby legs on the belly: sawfly larvae have six or more pairs, caterpillars five or fewer.
Why it happens
Sawflies are small wasps whose larvae feed on leaves. Each kind sticks to its own group of plants, such as roses, pines, gooseberries or pears.
How to fix it
- Pick larvae off by hand into soapy water, or knock young ones off with a strong spray of water.
- For heavy attacks of young larvae, spray horticultural oil or spinosad as the label says, never on open flowers, and keep kids and pets away.
- Don't use Bt; it only works on true caterpillars.
Keep it from coming back
- Check roses and other favorite hosts weekly from spring, while larvae are small.
- Avoid broad-spectrum sprays, so birds, parasitic wasps and beetles can help.
- Healthy shrubs and trees tolerate some feeding without lasting harm.
Sources
General guidance, not a diagnosis. For valuable, edible or outdoor crops, check with a local extension service or plant expert. Use any product exactly as its label says, and keep children and pets away while it dries.