How to identify it
- Fallen leaves are still green and carry only part of their stem; the cut end of the stem is often blackened.[1][2]
- The larvae are legless and cream-colored to white with a light brown head, about 1/3 inch long when full grown.[1][2]
- Adults are rarely seen: small wasp-like sawflies with a dark head and thorax and a light-colored abdomen.[1]
- Splitting the stub of stem still on the tree, near where the leaf broke off, should reveal the larva or its tunnel.[2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Gray squirrel clipping | Squirrels chew off whole twigs with leaves attached rather than single leaves.[1] |
| Drought, aphid or scale leaf drop | These cause leaves to drop later in summer, and the leaves are usually yellowed or discolored first.[1][2] |
Where it lives
It attacks maples, with sugar maple the preferred host; Extension services from Minnesota to Kentucky report it, and infestations there are usually limited to sugar maples.[1][2]
Biology and life cycle
It has one generation a year and spends the winter as a pupa in the soil.[1][2]
Adults appear in spring and lay eggs in leaf stems near the leaf blade; the larvae tunnel inside the stem for 20 to 30 days until it breaks and the leaf falls.[1][2]
The larva stays in the stub left on the tree; about 10 days later that stub falls too, and the larva leaves through a hole in its side to pupate in the soil.[1][2]
Damage and signs
Health risk
It is a leaf-stem borer of maples; Minnesota and Kentucky Extension mention no risk to people.[1][2]
Control
Sanitation
Raking the fallen leaves doesn't help, because the larvae are in the stubs still on the tree. Picking up and destroying the fallen leafless stubs, about 7 to 10 days after leaves start falling, kills larvae but only modestly reduces numbers.[1][2]
Pesticides
Insecticides are not recommended: the damage is minor and outbreaks are unpredictable.[1][2]
Common questions
- Why is my sugar maple dropping green leaves in June?
- If the leaves fall singly with part of the stem attached and a blackened end, maple petiole borer larvae tunneling in the leaf stems are a likely cause.[1][2]
- Will maple petiole borer kill my tree?
- No. The leaf drop has little effect on tree health, and treatment isn't recommended.[1][2]
- Should I rake up the fallen leaves?
- It won't reduce the problem, because the larvae are in the leaf-stem stubs still on the tree, not in the fallen leaves.[1][2]
Sources
- University of Minnesota Extension, “Maple petiole borer.” extension.umn.edu/tree-and-shrub-insects/maple-petiole-borer (accessed 2026-10-06)
- University of Kentucky Entomology (ENTFACT), “Maple Petiole Borer (ENTFACT-405).” entomology.entomology.prod-web.ca.uky.edu/files/ef405.pdf (accessed 2026-10-06)
- iNaturalist, “Caulocampus acericaulis taxon page (order and family).” www.inaturalist.org/taxa/495086 (accessed 2026-10-06)