Scale Insect Infestation on Star Magnolia: Identification and Control

Bob in Lansing, MI, finds hundreds of small, soft white blobs (pinky-nail sized) on his Star Magnolia branches. Crushing reveals a mushy brown center. The tree appears otherwise healthy.

Diagnosis: Scale Insects

These are almost certainly scale insects—likely a soft scale species. The "white blobs" are protective coverings over immobile adults feeding on plant sap. Crawlers (mobile nymphs) settle permanently, then secrete waxy covers. Heavy infestations cause yellowing, thinning, and dieback over time.

Control Options

Dormant Season (Best Timing)

• Dormant oil spray: Apply horticultural oil in late winter before bud break. Smothers overwintering scales. Follow temperature restrictions (typically below 85°F).

Growing Season

• Summer/ultra-fine oil: Safer for use in warmer weather.
• Systemic insecticide: Imidacloprid (e.g., Bayer Advanced Tree & Shrub) applied as soil drench. Roots absorb it; scales ingest it while feeding. Effective but slower.

Critical Timing

Target the crawler stage (usually late spring/early summer) for spray treatments. Your local nursery can advise on exact timing for your area.

Monitoring Success

Dead scales don't fall off immediately. Check for new infestation on current season's growth to gauge treatment effectiveness.