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Rhizoctonia Stem Rot This is one of the most important diseases on poinsettia as it kills plants in all stages of production. Rhizoctonia solani causes a light to dark brown water soaked lesion on the stem extending just above and just below the soil line. The lesion gradually expands until it encircles the stem. The lesion becomes slightly sunken and remains as a dry rot. Infection often begins during rooting and may kill plants before or after transplanting. If the disease progresses slowly, plants may not die until mid- to late-November.
Plants with stem rot may be stunted, lower leaves may abscise, upper leaves may be chlorotic and the leaf edge may curl upward along the midrib. The disease progresses rapidly, the foliage wilts suddenly and plants fall over and die. In later stages of the disease, roots may also be discolored. Development of Rhizoctonia stem rot is not affected by pH. Disease development increases as soil temperature is increased from 17 to 26°C (60 to 80°F). Soil moisture levels below 50% moisture holding capacity (MHC) are not favorable for Rhizoctonia stem rot and a MHC above 80% retards disease development.
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