Armillaria Root Rot
Armillaria mellea, Armillaria spp.
Overview
Armillaria root rot (honey fungus) kills woody plants by invading roots and the root crown, spreading through soil on dark rhizomorphs that can persist for decades in old roots and stumps. Orchards, food forests, and ornamental plantings on previously wooded ground are at highest risk. Armillaria Root Rot spreads mainly by spores on wind, splash, tools, and crop debris. Humid, crowded plantings and overhead watering favor outbreaks in home gardens and food forests. Causal agent: Armillaria mellea, Armillaria spp.. In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Gradual decline, yellowing, wilting, and branch dieback. White mycelial fans under bark at the crown; dark shoestring rhizomorphs on roots; honey-colored mushrooms may fruit at the base in autumn. Trees often fail to push strong spring growth before dying. Compare several plants and note whether symptoms spread after rain, insect feeding, or wet foliage. Photograph undersides of leaves and cut stems when wilt is present to refine the diagnosis. Rule out simple drought, fertilizer burn, and herbicide drift before assuming a pathogen - abiotic injury often mimics disease.
Environmental Conditions
Humid
Prevention
Clear old stumps and major roots before planting. Improve drainage and avoid chronic waterlogging. Keep trees vigorous but not overwatered. Choose species known to tolerate Armillaria in your region when replanting infested ground. Mulch to reduce splash, clear season-end debris, and avoid working plants when wet. Design beds for airflow and diverse plantings that support beneficial insects without creating permanent humid pockets around susceptible crops.
Management
There is no reliable chemical cure. Remove infected plants with as much root mass as possible. Expose the root crown to air by pulling soil back. Avoid replanting highly susceptible species in the same spot. Soil sanitation and resistant replacements are the practical tools. Prefer drip irrigation, morning watering, and open spacing so leaves dry quickly. Disinfect pruners between cuts on woody plants. Use copper, sulfur, or biological products only as labeled protectants when pressure is high - they rarely reverse advanced infections alone. Destroy (do not casually compost) highly infectious debris.