Oak Root Fungus: Identification, Management, and Prevention

Understanding Armillaria mellea

Oak root fungus (Armillaria mellea) attacks various woody plants, prevalent in the Southeast and low-elevation, non-desert California. Early symptoms: dull, yellowed, or wilted leaves; sparse foliage. Later, entire branches die as root death cuts off water/nutrient supply.

Diagnosis

Check under bark of large roots or trunk near ground level for whitish fungal mats. In late autumn/early winter, tan mushrooms may cluster at infected plant bases.

Management and Prevention

• Lightly infected plants may be saved by exposing root-trunk junction to air (remove soil) and cutting out all dead/infected tissue.
• Choose resistant plants; avoid susceptible species in known Armillaria areas (e.g., old orchard sites).
• If replanting where a plant died from Armillaria, remove and destroy all roots in the planting area.

No chemical control exists.