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Root Rot
Root rot has become increasingly serious on dry beans in North Dakota and has reduced yields in some fields.
Several fungi cause root rot, including Rhizoctonia solani and Fusarium spp. These fungi are soil borne and are more common where beans have been grown for many years. These fungi attack the roots. Fusarium causes reddish-colored lesions with no borders; later the lesions turn dark brown. Rhizoctonia causes brick red lesions with definite, dark borders. If roots are heavily infected with either pathogen, upper plant parts are yellowed and stunted and often wilted.
Upper plant symptoms are more obvious when drought, salt, or other field conditions prevent lateral (secondary) root development. The disease is most commonly observed during mid to late season.
CONTROL
Long rotations can help keep the amount of fungus in the soil at low levels. Hilling soil around the base of the plant can stimulate lateral root development, but close cultivation can trim shallow roots, and deep cultivation can bring weed seeds above the herbicide layer. Avoid soil compaction.
Avoid short rotations involving dry beans, soybeans and sugarbeets, since all are
susceptible to the same strains of Rhizoctonia.
Varieties with tolerance to Fusarium root rot are available (see Circular-654, North Dakota Dry Bean Performance Testing). Plant tolerant varieties in fields where root rot has been a problem.
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