Diagnosing Dying Lilacs: Borers, Disease, and Cultural Fixes

Branch-by-branch decline in lilacs signals serious issues. Three main categories:

1. Insect Borers

Check for small entry holes in stems. Lilac borers tunnel inside, cutting off water flow. Prune out infested branches well below damage.

2. Fungal Diseases

• Powdery mildew: Cosmetic, white coating on leaves
• Botrytis blight: Serious—causes shoot dieback, especially in wet springs

3. Cultural Problems

• Automatic irrigation = too wet
• Drought stress = too dry
• Poor drainage = root rot

Immediate Action Plan

1. Water deeply once weekly (not frequent shallow watering)
2. Apply composted cow manure around base
3. Remove all dead wood
4. Check for borer holes
5. Consult Connecticut Agricultural Experiment Station lilac guide

Lilacs prefer sweet (alkaline) soil. If your soil is acidic, add lime. With corrected care, lilacs often recover remarkably.