Rhizoctonia solani is a soil fungus with a wide host range and worldwide distribution. Its host plants include virtually all vegetables, flowers, shrubs and trees. It can cause serious damage to the plant by attacking the roots, stems, bulbs, base and other parts of the plant in and above the ground. The most common symptoms are root rot and stem rot. The fungus can also cause sunken patches on fruits.

The effect of the fungus is also known as ‘damping off’ as it causes the stem to die off at ground level. Very young plant material can even die off before or immediately after the seedling emerges from the ground. The fungus is mainly found in soil-grown crops such as radish, lettuce, bean, chrysanthemum and summer flowers, but it also occurs in pot and bedding plants.

Rhizoctonia does not produce asexual spores. The pathogen overwinters as mycelium or sclerotia. Strands of mycelium can then appear in favourable conditions. The fungus spreads via water, tools carrying soil particles, and other contaminated materials. The optimum temperature for infection is between 15 and 18ºC.

Text: Andrea Disco. Image: Wageningen University & Research.