Lilac and Catalpa Leaf Curl in Montreal: Heat, Pests, or Herbicide?

Investigating the Cause

Simultaneous leaf curling on mature lilacs and catalpa in Montreal—with ash unaffected—suggests a shared environmental or chemical stressor. Lawn service treatment (even without pesticides) may involve broadleaf herbicide drift or volatilization—common cause of cupping/curling on sensitive species.

Diagnostic Steps

1. Check leaf undersides for spider mites (moving specks on white paper) or aphids.
2. Review lawn service records: Ask about 2,4-D, dicamba, or similar products applied recently.
3. Assess weather: Sudden heat/drought after cool spring causes physiological curl.

Action Plan

• If herbicide suspected: Water deeply to leach soil; do not fertilize; wait for new growth.
• If mites/aphids: Spray neem oil or insecticidal soap on undersides.
• If heat stress: Mulch, water 1 inch weekly, avoid overhead irrigation.

Catalpa and lilac are both herbicide-sensitive; ash is tolerant—this pattern strongly implicates lawn chemical drift.