Rhizoctonia root rot

Pathogen and disease type. Rhizoctonia root rot is a common and destructive disease caused by the soil-borne basidiomycete Botryobasidium vagum (anamorph Rhizoctonia solani). This pathogen acts as a saprophyte and parasite, attacking roots, stems, and tubers, leading to various types of rot, damping-off, and stem cankers.

Host crops. The fungus has an extremely broad host range, infecting almost all major agricultural crops. Significant economic losses are reported in potatoes, sugar beets, cereals, turfgrass, and a wide array of vegetable crops such as tomatoes, cucumbers, and legumes.

Symptoms and signs. Symptoms depend on the crop and stage of infection. In potatoes, the most characteristic sign is the presence of black, hardened sclerotia on the tuber surface, known as black scurf. Seedlings often experience pre-emergence damping-off, while older plants may exhibit sunken brown cankers on stems, leading to stunted growth or premature wilting.

Development and damage. The disease thrives in cool to moderate soil temperatures and high moisture conditions. The pathogen survives in the soil through sclerotia or as mycelium on crop debris for several years. Damage is characterized by stand reduction, decreased vigor, and significant yield losses due to tuber blemish or root destruction.

Control and prevention. Management requires a combination of cultural and chemical strategies:

• Implementing diverse crop rotations to minimize pathogen buildup in the soil.
• Planting only high-quality, disease-free seed or certified tubers.
• Applying seed or tuber treatments with effective systemic or contact fungicides.
• Avoiding planting in cold, wet soil to reduce the duration of the vulnerable seedling stage.
• Incorporating bio-fungicides, such as Trichoderma species, to suppress pathogen activity in the rhizosphere.