Lilac Trunk Borers: Organic Controls for Ontario Gardens

Small holes in lilac trunk indicate borers (likely lilac borer moth larvae). Pesticide bans in Ontario mean organic options only.

Organic Treatments

• Bt (Bacillus thuringiensis): Spray on trunk in spring when eggs hatch (Dipel, Green Step, MVP). Kills young larvae.
• Diatomaceous Earth: Dust trunk and soil base. Abrasive powder dehydrates crawling larvae.
• Beneficial Nematodes: Steinernema carpocapsae applied to soil around base—parasitize larvae.

Cultural Care

1. Prune dead/damaged wood.
2. Water deeply during drought.
3. Mulch (not against trunk) to reduce stress.
4. Healthy lilacs resist borers better.

Monitor annually; treat at first sign of fresh sawdust.