Flip a chewed dogwood leaf. A dozen white, powdery worms on the underside are dogwood sawfly. Knock them into soapy water. A Bt spray made for moth caterpillars will not kill them.
Dogwood sawfly is a native wasp relative, Macremphytus tarsatus. The adult is a slender, shiny black, wasp-like insect that does not sting. The larva changes look as it grows: first a tiny yellow translucent worm, then a white waxy coat, then cream with black spots, then yellow and black and about an inch long. One generation a year. It feeds on dogwood leaves, especially shrubby kinds such as red-osier, gray, and tatarian dogwood.
- Flip the leaf. White powdery worms in a group confirm it.
- Pick them into soapy water. Bt will not finish them.
- Late chew on a healthy shrub is looks, not a dead plant.
Pick the larvae into soapy water; skip Bt
They feed on the undersides, often a dozen or more on one leaf, so the top of the shrub can look fine until a branch is already skeletonized. Flip chewed leaves from July into September. Knock the group into a bucket of soapy water, or crush them. Shake a small shrub over a sheet and finish what drops. Wear gloves and long sleeves on blood-twig dogwood, because the foliage can raise an itchy rash.
Bt, the Bacillus product sold for moth and butterfly caterpillars, does not kill this insect. It is a sawfly, related to bees and wasps, not a moth. Fail if the plan is a Bt spray on the white powdery worms. Large, yellow-and-black larvae that are already near an inch long shrug off soap and oil too. Those you pick by hand.
Does Bt kill dogwood sawfly?
No. Bt kills moth and butterfly caterpillars. This is a sawfly. Pick the larvae, or use soap or oil while they are still small and you can hit the undersides.
Flip the leaf: white powder worms in a group
The first useful sign is chewed dogwood foliage with the insects still on the underside. Young larvae skeletonize the leaf and leave the veins. Older ones eat everything but the midrib. They rest curled up and can look like bird droppings. You do not need to see the adult. The group on the leaf is the confirm.
Eggs sit in the leaf as small bumps in rows along the veins. Those bumps turn brown. First-stage larvae are tiny, yellow, and hard to spot. After a molt they put on a white, powdery wax. After the last molt they lose that coat, turn cream with black spots, then yellow and black, and wander off the plant. Count the fleshy back legs behind the three true pairs: six or more means sawfly. Five or fewer means a moth caterpillar, and that insect takes a different bottle.
| Where you see it | What it is | Try this |
|---|---|---|
| White powdery worms in a group on the underside; veins then midrib left | Dogwood sawfly | Pick into soapy water |
| Tiny yellow translucent worms, then a white coat, on chewed dogwood | Same insect, younger | Pick, or soap while they are small |
| Brown bumps in rows along the leaf veins | Eggs of this sawfly | Watch that leaf; pick when they hatch |
| Yellow-and-black inch-long worms leaving the shrub | Last stage, heading to wood | Pick; they have mostly stopped feeding |
| Dark spots, blighted hanging leaves, dieback from the foliage | Anthracnose leftover | See that disease — not chew |
| Metallic green beetle and irregular lacy holes | Japanese beetle leftover | See that pest — not this worm |
| Reddish sawdust on wounded bark | Dogwood borer leftover | See that pest — not a leaf chew |
| Club or spindle on a twig tip | Clubgall midge leftover | See that pest — not a sawfly |
Chewed leaves are not a moth caterpillar or anthracnose
A moth caterpillar has five or fewer fleshy back legs and often hooks on those legs. This sawfly has six or more and a hairless body. The bottle that kills cabbageworms will miss it. Do not treat a white powdery group on red-osier as a tent caterpillar or a hornworm.
Dark spots that blight whole leaves, then move into twigs, are dogwood anthracnose. That is a fungus. There is no worm on the underside. See dogwood anthracnose. A metallic green beetle chewing irregular holes is Japanese beetle. See Japanese beetle. Do not run that trap method here.
Reddish sawdust at a wound on the trunk is dogwood borer. See dogwood borer. A wilted twig with a row of holes is dogwood twig borer. See dogwood twig borer. A spindle swelling on a tip is dogwood clubgall midge. See dogwood clubgall midge. A slug-like film on pear is a different sawfly. White powdery worms on birch are not this insect. Do not run those methods as the dogwood finish.
Late chew on a healthy shrub can wait
Most of the feeding shows in late summer. On an established red-osier, gray, or tatarian dogwood, that late defoliation is ugly and it is not a dead plant. The shrub leafs out again next spring. Plant death from this insect is uncommon. Do not spray a stripped shrub in August when the larvae have already walked off.
Pick this season if a young shrub is being stripped while it is still putting on wood, or if last year was heavy and the same plant is thin again. Flowering dogwood and kousa usually take this less than the twig dogwoods. A few groups on a large, still-dense shrub can wait. Water the plant you mean to keep so the next flush has moisture. Do not pile extra fertilizer on a defoliated shrub in late summer.
Will dogwood sawfly kill my shrub?
Usually no. Late-summer chew on an established red-osier or gray dogwood is looks. A young shrub stripped while it is still growing is the case to pick this year.
Soap and oil only work while they are still small
Insecticidal soap, horticultural oil, and spinosad can kill young larvae if the spray actually hits them. They sit on the undersides, so a pass over the tops misses the job. Spray in the evening. Cover the undersides. Repeat only as the label allows. Skip the mix when the air is hotter than about 85°F, because oil on hot foliage can burn the leaf.
Once the larvae are near an inch long they are tough. Soap and oil then waste a trip. Pick those by hand. A labelled contact product is last, and only on a young shrub you mean to keep after a heavy year. Skip the brand aisle as the whole plan. Neem is an oil; it has to hit the insect. It will not bring back a leaf that is already eaten.
Does neem oil kill dogwood sawfly?
Only if it contacts the larva, the same as any horticultural oil. Coverage on the undersides is the job. Older larvae are tough. Neem will not bring back a leaf that is already eaten.
Why didn't insecticidal soap work?
The larvae sit on the undersides, so a top-only spray misses them. Large larvae near an inch long are not very susceptible. Pick those. Soap is for the small, white-coated stage.
Yellow-and-black wanderers in the deck are not eating the wood
When they finish feeding they crawl off the dogwood and chew a small cell in soft or decaying wood for winter. Logs, landscape timbers, a rotted deck board, and sometimes outdoor furniture get those chambers. They are not termites. They do not eat the lumber. They cut a hole to spend the winter, then the adult cuts out in late spring.
Pick the yellow-and-black worms off the deck, the fence, and the sill and drop them in soapy water. A spray on a wandering last-stage larva does little, because it has stopped feeding on leaves. Next year, pick the white groups on the dogwood in July so fewer of them reach the wood. Do not treat reddish frass on living bark as this insect. That is dogwood borer in the trunk.
Are they eating my deck?
They chew a small winter cell in soft or decaying wood. They do not eat the lumber the way a termite does. Pick the yellow-and-black wanderers. Next July, pick the white groups on the dogwood.
Confirm, pick, or wait
- Confirm. Flip a chewed leaf. White powdery worms in a group, or yellow-and-black worms that just left the coat. Six or more fleshy back legs. No worm and a blighted hanging leaf is a different problem.
- Pick the group into soapy water. Shake a small shrub. Wear gloves on blood-twig dogwood.
- Wait on a few groups on a healthy, established shrub in late summer. Do not wait on a young shrub that is losing most of its leaves while it is still growing.
- Spray last. Soap, oil, or spinosad on small larvae, undersides, evening. Skip Bt. Skip a spray on inch-long yellow-and-black wanderers.
- Pick wanderers off the deck and the timbers. They are making a winter cell, not eating the house. Fail if the finish is Bt and you never flipped a leaf.
Related reading
- Dogwood borer — frass and wounded bark on the trunk, not a leaf chew.
- Dogwood twig borer — wilted individual twigs and girdled tips, no white powder worms.
- Dogwood clubgall midge — a club on the twig, not a group on the leaf.
- Dogwood anthracnose — blighted leaves and twig dieback from a fungus.
- Japanese beetle — a metallic beetle chewing irregular holes, not a sawfly larva.
FAQ
Do dogwood sawflies bite or sting?
No. The adult looks like a small wasp and does not sting. The larvae chew leaves. Wear gloves on blood-twig dogwood because the foliage, not the insect, can itch.
When should I look for them next year?
One generation a year. Adults fly from late spring into July. Start flipping undersides in early July. The white coat is easy to see. Do not wait until September when the leaves are already gone.
Related pests
Related diseases
Updated: Reviewed by Bosquelle Editors