Rhizoctonia Root Rot
Rhizoctonia solani
Overview
A soil-borne fungal disease causing damping off, root rot, and stem cankers in a wide range of plants. The fungus survives as sclerotia in soil and plant debris and is favored by warm, moist conditions. Rhizoctonia 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: Rhizoctonia solani. In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Reddish-brown, sunken cankers on stems at or near the soil line. Root rot with brown, firm lesions. Damping off of seedlings. Wire stem in brassicas. Brown patch in lawns. Web blight on foliage in humid conditions. 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
Rotate crops. Avoid planting too deep. Ensure good drainage. Do not over-fertilize with nitrogen. Use clean transplants. Avoid compacting soil. 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
Improve drainage. Apply biological controls (Trichoderma). Fungicide seed treatments. Avoid excessive irrigation. Remove infected plants. Solarize soil between crops. 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.