Dogwood borer

About

The larva of a small clearwing moth that tunnels in the inner bark of flowering dogwood and other trees, including apple, flowering cherry, oak, birch and blueberry (UMass). The larvae can't chew into healthy bark, so they get in through wounds, cracks and branch crotches; kousa dogwood seems to resist it.

Spotting it

Damage

Larvae make winding tunnels under the bark and push out coarse, brown, sawdust-like frass. Bark loosens and cracks, the area can swell into knotty, callused bumps, and branches die back; heavily infested older trees can hang on for years (UMass).

How to find it early

Check trunks, especially mower and string-trimmer scars, bark cracks and branch crotches, for brown frass and loose bark. Empty pupal skins may stick out of the bark after moths come out (UMass).

When

Moths fly late spring through September; larvae are under the bark all year.

Life cycle

Usually one generation a year, though it may take two years in cold areas and more than one generation in warm ones. Adults start flying when dogwood flowers drop and keep flying into September; females lay eggs on wounded bark, and the larvae crawl around to find a way in (UMass).

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Avoid wounds Prevent

   Keep mowers and trimmers away with a mulch ring, don't prune while moths are flying, and keep trees vigorous. Where the borer is common, consider kousa dogwood (UMass).

   Vinyl tree wraps on young dogwoods have been reported to increase infestations (UMass).

2. Cover fresh wounds Barrier

   Painting fresh bark wounds with white latex paint has been suggested to keep egg-laying moths away (UMass).

3. Beneficial nematodes Natural enemies

   Insect-attacking nematodes sprayed into infested bark have given very good results; choose a species labeled for dogwood borer and water it in (UMass).

   Nematodes are living and need careful storage and handling (UMass).

4. Trunk spray when moths fly Conventional spray

   Contact sprays go on the trunk and lower branches to hit egg-laying moths; New York reports suggest spraying about 10 days after the first moth is caught in a pheromone trap. Active ingredients include chlorantraniliprole, bifenthrin and permethrin (UMass).

   Spray after dogwood bloom and when bees are not active (UMass); bifenthrin is highly toxic to bees (PNW 591). Follow the label.

Plants it goes after

Apple (backyard tree), Blueberry, Flowering cherry, Flowering dogwood, Oaks (white, red and pin oak), Red twig dogwood

Pressure by region

Ratings are estimates based on where flowering dogwood is commonly grown.

Ratings come from extension sources where available; some are estimates, as noted above.