What is Rhizoctonia Solani?

Mary McMahon

Rhizoctonia solani is a fungus found in soil and known to infect plants, causing fungal diseases like collar rot, wire stem, and damping off. Infection with this fungus is usually fatal and often occurs in seedlings. There are a number of measures available for control of this fungus that can be used to reduce the risks of fungal infection in plants and to manage existing outbreaks.

Seedlings can be infected by Rhizoctonia solani.
Seedlings can be infected by Rhizoctonia solani.

This fungus produces a white, thready mycelium and when an infection is active, may appear in the form of small threads around the base of the plant. Plants infected with Rhizoctonia solani typically develop reddish to brown sunken spots. The spots spread, causing the plant to soften, wilt, and fall over. A common form of infection is a collar rot, where the fungus rings a developing stem, cutting off the supply of nutrients to the rest of the plant. When it infects the main stem of a seedling, the whole seedling will die.

Damping off, a common fungal disease of seedlings, can be caused by Rhizoctonia solani along other fungi. Plants infected with fungus soften, turn mushy, and die. Sometimes, the infection starts very early in the germination process, before the seedling has even had a chance to sprout. In wire stem, a disease involving older plants, rot and scarring constrict stem size, limiting growth and depriving plants of the nutrients they need.

Controlling this soilborne pathogen requires promptly removing and burning or otherwise safely disposing of infected plants. Infectious plant material should not be composted, as the fungus can live in the compost and will cause a recurrence of the infection when the compost is applied to plants or mixed with soil. Soil treatments are available, with fumigants to kill the fungus so it cannot spread.

Gardeners can also abandon soil infected with Rhizoctonia solani for several planting cycles. Without nutrition, the fungus will eventually die off, and the soil can be used again. Soil sterilization will ensure that there are no traces of this fungus or other infectious organisms in the soil.

While it can be frustrating to lose a crop to Rhizoctonia solani, it is important to act quickly and decisively to halt the spread of the fungus. When working in environments like greenhouses, maintaining a drier and slightly cooler environment can inhibit fungal growth, and it is important to avoid moving or mixing greenhouse trays, so that in the event of a fungal invasion, infected trays can be quickly and easily removed to prevent the fungus from spreading throughout the entire facility.

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