Key Features
- Stunting, wilt, or dieback
- Stem rot at soil line
- Brown roots
Symptoms
Rhizoctonia is responsible for causing seedling death, leaf blights, stem cankers, and crown and root rots. In a dense planting, Rhizoctonia creates pockets of collapsed, dying, and dead plants. The pathogen attacks stems at the soil-line, often causing a sunken, dry rot that results in stem breakage where the stem meets the soil. Strands, or even mats, of the fungus may form on the stem at the soil-line. Early crown and root rot symptoms include wilting, reduced growth, yellowing, and dieback. Irregular spots may be present on leaves, especially those in contact with soil. Infected roots are discolored (yellow to black), have sections of decaying roots, and fail to develop new roots. Symptoms of Rhizoctonia root rot appear similar to many root rots like Pythium, Fusarium, and Phytophthora. Laboratory diagnosis is essential to identify the pathogen and develop a sound management strategy for control of this disease. Many fungicides labeled for control of Pythium or Phytophthora root rot are ineffective against Rhizoctonia.
Biology
Rhizoctonia survives as soil-borne spores in the absence of a host. Infection occurs at the soil line or on leaves and stems that are either touching the ground or have been splashed by soil or litter containing the the pathogen. Symptoms of Rhizoctonia can develop within a week. Rhizoctonia thrives in humid conditions that form under the thick canopy of vigorously growing plants. It escapes notice until it causes the rapid collapse of large sections of a plant or plants. The pathogen can move between plants through soil or when mycelia growing on the plant surface touches another plant. People, animals and flowing water often spread Rhizoctonia. Unlike most plant pathogens, Rhizoctonia does not produce spores, but spreads between plants by producing thin strands of fungal threads called hyphae.
Management Recommendations
Inspect plants for Rhizoctonia prior to purchase to decrease chances of introducing the fungus to new plantings. Always remove infected plants as soon as possible to prevent inoculum from building in the soil. Anything that spreads contaminated soil (such as workers, run-off, pets, and insects) can spread Rhizoctonia. Remove infected plants as soon as symptoms appear. Replant with less susceptible plants. Chlorothalonil is labeled for Rhizoctonia web blight control, though infected plants are likely to develop root and crown infections that will not be prevented by fungicide sprays. Thiophanate-methyl has given inconsistent results for the control of Rhizoctonia.
Effective Pesticides
Active Ingredients include: Chlorothalonil, Thiophanate-methyl
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
