Pest profile

Rhododendron Borer

Synanthedon rhododendri · Lepidoptera: Sesiidae[2]

Rhododendron borer is an important wood-boring pest of rhododendrons and occasionally azaleas.[1]

Rhododendron borer moth, a wasp-like clearwing moth with a black body and yellow bands
Rhododendron borer moth, a wasp-like clearwing moth with a black body and yellow bands. (c) Bill Keim, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • The adult is a clearwing moth that looks like a wasp.[1]
  • Larvae are pale yellow with a dark head, about 1/2 inch long, tunneling inside branches.[1]

Look-alikes

Look-alikeHow to tell them apart
Paper waspsThe adult moth resembles a wasp.[1]

Where it lives

HGIC covers it on rhododendrons and azaleas in South Carolina.[1]

US map: public records from 13 states since 1990 (GBIF).

Biology and life cycle

Females lay eggs on the bark; larvae bore in and make long tunnels within branches.[1]

By late fall larvae enter the sapwood to overwinter.[1]

Damage and signs

  • Leaves on infested branches turn off-color and wilt, like drought stress; damage is most noticeable in fall.[1]

Health risk

It feeds on plants; Clemson HGIC mentions no risk to people.[1]

Control

Sanitation

Prune and destroy wilted or infested branches.[1]

Traps and physical control

Cut open wilted branches to look for larvae, and use pheromone traps to detect male moths.[1]

Pesticides

Permethrin can protect trunks and branches from newly hatched borers.[1]

Common questions

Why are some rhododendron branches wilting in fall?
Rhododendron borer larvae tunneling inside can cause wilting that looks like drought stress.[1]
How do I confirm rhododendron borer?
Prune a wilted branch and cut it open to look for pale yellow larvae.[1]

Sources

  1. Clemson Cooperative Extension, Home & Garden Information Center, “Azalea & Rhododendron Insect Pests (HGIC 2051).” hgic.clemson.edu/factsheet/azalea-rhododendron-insect-pests/ (accessed 2026-10-06)
  2. iNaturalist, “Synanthedon rhododendri taxon page (order and family).” www.inaturalist.org/taxa/417076 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.