Grevillea Dieback: Root Rot Management in Affected Beds

Diagnosis: Phytophthora Root Rot

Multiple genera dying in proximity = soil-borne root pathogen, likely Phytophthora (cinnamon fungus) in Australian natives. Symptoms: sudden wilt, death, no foliar pathogens visible.

Immediate Treatment

1. Remove dead/dying plants: Bag and dispose (don't compost).
2. Soil drench: Phosphorous acid (e.g., Agri-Fos, Fosphite) or metalaxyl (Subdue) per label. Apply to surrounding plants' root zones.
3. Improve drainage: Mound beds, add coarse sand/compost, avoid irrigation runoff.

Prevention for Replanting

• Choose resistant species (many Grevillea hybrids are susceptible).
• Plant on mounds.
• Use phosphorous acid as preventive drench 2×/year.
• Sterilize tools between plants.

Daconil (chlorothalonil) is a foliar fungicide—ineffective for root rot. Use phosphorous acid or metalaxyl for soil treatment.