Lilac/Ash Borer
Podosesia syringae
A clearwing moth that mimics a harmless wasp as an adult and whose larvae bore into the lower trunks and stems of lilac, ash, and privet. Tunneling in the wood restricts water and nutrients, causing dieback, swelling, cracking, and easily broken stems.
🔎 How to spot it
The adult is a brown clearwing moth with clear hind wings that closely resembles a paper wasp, though it cannot sting. The larvae are creamy white caterpillars about an inch long with brown heads that tunnel in the wood near the ground. Look for round exit holes, coarse sawdust-like frass, and swollen, cracked bark at the base of stems.
🥀 Damage it causes
Larvae tunnel under the bark and into the wood, usually near the ground, restricting water and nutrient flow and causing shoots and branches to die back. Infested areas swell and crack, and weakened stems break easily in wind. A secondary fungus can invade the borer wounds and add to the damage.
🛡️ Prevent it
Keep plants vigorous with proper watering and avoid wounding the lower trunk, since females lay eggs in cracks, rough bark, and wounds. Prune out and destroy heavily infested stems. Pheromone traps are available to track adult flights and time any treatment.
🧯 If it is already here
Time trunk sprays of permethrin or another labeled pyrethroid to egg hatch, generally around the first and third weeks of May in many regions and guided by trap catches. Thoroughly wet the lower trunk and structural branches. There is no reliable rescue once larvae are deep in the wood, so prevention and timing matter most.
💡 Good to know
There is one generation a year, and the borer overwinters as larvae in the wood near the ground. Adults fly from roughly April into June. The cultivar Marshall Seedless ash and stressed, recently transplanted trees are especially prone.
🌱 Plants it attacks
4 plants in the library can be attacked by this pest
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.