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Plant & Pest Advisory – May 27, 2025 – Andy Wyenandt
Rhizoctonia root rot has been reported over the past week. Rhizoctonia root rot, caused by
Rhizoctonia solani, is an important soil-borne fungal pathogen with a very large host range.The
pathogen can survive saprophytically on living or dead plant material (organic matter) oras sclerotia in
the soil (for more than 3 years). Disease development is favored by warm temperatures, dry (or very
well drained) soils and stressed plants. Symptoms of Rhizoctonia root rot may begin as stunted plant
growth (with poor root systems) with the appearance of brown lesions at the base of the stem causing
wilting with lesions eventually girdling the stem and killing the infected plant. Rhizoctonia root rot
infections only extend about an inch above the soil surface, unlike Phytophthora blight infection which
can extend much farther up the stem.
Additionally, in root systems infected by Rhizoctonia, the outer cortex of the root system won’t slough
off, like it does with Pythium root rot infections. Under ideal conditions, the mycelium of the fungus
growing can be seen with a 10x hand lens growing along the root surface. Rhizoctonia produces
distinct, brown hyphae that almost always branches at nearly 90 degree angles and is a diagnostic
feature of the fungus. Rhizoctonia root rot often shows up in transplant production when plug trays
are held on the dry side for extended periods, often when growers reduce water to control transplant
growth. Infected transplants may not show symptoms until after they are set in the field. Infected
transplants or plants infected shortly after transplanting often remain short and stunted with poor root
systems compared to healthy plants. This most often occurs when the top of transplant plug has not
been sufficiently covered over by soil, the lack of water used in setting the transplant, or when drip
irrigation systems have not been hooked up and the soil less media becomes excessively dry for a
period of time after transplanting.
Control of Rhizoctonia root rot begins with recognizing its symptoms, so as not to confuse it with
other soil-borne diseases, proper watering and irrigation pre-, at-, and post-transplanting, and
preventative fungicide control measures post transplanting. For more information on the control of
Rhizoctonia root by crop please see the 2024/2025 Commercial Vegetable Production
Recommendations Guide.