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Effect of crop rotation and tillage on Rhizoctonia root and crown rot and Rhizoctonia solani AG 2-2 soil populations

Audrey Kalil: North Dakota State University, Williston Research Extension Center

<div>Rhizoctonia root and crown rot (RRCR) caused by <em>Rhizoctonia solani</em> AG 2-2 IV and IIIB is a devastating disease of sugar beet (<em>Beta vulgaris</em> subsp. <em>vulgaris) </em>in Montana and North Dakota. Small grain crops such as barley are not susceptible to <em>R. solani</em> AG 2-2 and thus barley-beet rotations are common. Tillage is also recommended for control of residue-borne fungal pathogens such as <em>R. solani,</em> and intensive tillage has for many years been common practice in sugar beet production. Growers are increasingly choosing to rotate sugar beet with <em>R. solani</em> AG 2-2 susceptible crops such as soybean and corn and practice reduced tillage to improve soil health. It is unclear how these practices will impact inoculum levels and RRCR risk. Barley-beet and corn-soy-barley-beet crop rotations managed with either full or reduced tillage were evaluated for RRCR. Soil populations of <em>R. solani</em> AG 2-2 were measured under these treatments using quantitative real-time PCR. Soil samples collected prior to planting contained higher levels of <em>R. solani</em> AG 2-2 under the barley-beet rotation, possibly due to the shorter rotation between sugar beet crops. The corn-soy-barley-beet rotation increased crown rot severity in comparison to the barley-beet rotation while there was no difference in root rot severity and post-harvest soil populations of <em>R. solani AG 2-2</em>. Reduced tillage did not increase RRCR or soil populations of <em>R. solani AG 2-2</em>.</div>