Rhizoctonia

Rhizoctonia is a serious fungal disease caused by the basidiomycete Thanatephorus cucumeris (anamorph Rhizoctonia solani). This pathogen is known for its wide host range, impacting various economically important crops such as potatoes, turfgrass, vegetables, and legumes, often causing severe crop failure if left unmanaged.

The disease primarily manifests as root and stem rot. On potato tubers, it is characterized by the presence of black, crusty sclerotia, often called "black scurf". In young seedlings, the fungus causes "damping-off," a condition where the stem decays at the soil line, causing the plant to collapse and die shortly after germination.

Primary symptoms include dark, sunken lesions on stems and roots, stunted plant growth, and yellowing foliage. Under high humidity, a characteristic white mycelial web may appear on the base of the stems. Because the fungus thrives in the soil, it significantly damages the underground vascular system of the host plant, preventing nutrient uptake.

Development of the disease is highly dependent on environmental conditions. It is most aggressive in cool, moist soil temperatures, which hinder rapid seed germination and seedling emergence, giving the pathogen an advantage. Soil compaction, poor drainage, and excessive irrigation are major environmental factors that facilitate the rapid spread of the mycelium throughout the field.

Effective management strategies for Rhizoctonia include:

• Utilizing disease-free certified seeds and tubers.
• Implementing long-term crop rotation cycles.
• Applying seed treatment fungicides prior to planting.
• Improving soil drainage to prevent moisture buildup around roots.
• Managing irrigation levels to maintain optimal soil aeration.