Identifying Grub Damage vs. Other Causes of Shrub Decline

Weigela and salvia dying with basal browning; rhododendrons/azaleas died previously. Owner suspects grubs but saw only a few at planting.

Grub Threshold

Dig 1 sq ft. 15+ grubs = problem. Under 10 = look elsewhere.

More Likely Causes

• Phytophthora root rot: Poor drainage, overwatering. Watch moisture.
• pH out of range: Test and adjust.
• Vole damage: Dime-sized holes/tunnels under mulch. Voles eat roots fast.
• Over-amended soil: Use native soil + ≤1/3 organic matter.
• Planting too deep: Always plant high.

Follow-Up: Root Rot Confirmed

Infected plants rarely worth saving. Apply Agri-fos (Monterey) if sentimental, but must fix drainage. Replace with water-tolerant shrubs: Virginia sweetspire, buttonbush, summersweet, althea.