Diagnosing Black Spots on Petunias: Aphids vs. Fungal Issues

Tiny black spots on petunia tips in Denver's heat could be either black aphids or fungal leaf spot. The diagnosis determines treatment.

Identification Test

Touch the spots: If they crush under your fingers, they're black aphids—common on new growth and easily controlled. If they don't crush, suspect fungal leaf spot from frequent foliage wetting.

Treatment Protocol

1. Drainage first: Poke holes in pots without drainage—essential regardless of issue
2. If aphids: Spray with insecticidal soap, blast with water, or crush manually
3. If fungal: Trim affected tips (promotes bushier growth anyway), remove severely affected branches to 4 inches above basket
4. Watering adjustment: Water mornings only, avoid wetting foliage
5. Fertilize properly: Feed after watering every 3-4 weeks or use time-release product

Ongoing Petunia Maintenance

Petunias bloom only on branch tips. Prune a few branches back every other week to maintain continuous flowers all summer. Denver's dry climate actually helps reduce fungal issues if foliage stays dry.