Rhizoctonia root rot is a serious disease problem in several sugarbeet-growing regions, with the result sometimes being dramatic — and expensive — reductions in tonnage and quality. Low levels of infection can easily cause yield losses in excess of a ton per acre, while high infection levels can cut yields by more than 10 tons per acre. The quality of surviving beets can also be impacted, sometimes resulting in significant losses in recoverable sugar.
Though sugarbeet producers in western states have dealt with significant levels of Rhizoctonia crown and root rot for many years, the disease’s development as a serious problem in the Red River Valley and Southern Minnesota growing areas is a more-recent phenomenon.
A key factor in Rhizoctonia’s “Upper Midwest expansion” over the past several years is cropping patterns. There now are fewer wheat and barley fields (nonhost crops) and more corn, soybean and edible bean fields (all host crops). That has translated into more disease inoculum present in soils to threaten sugarbeet crops that follow corn or beans. “We think the number-one driver [behind the increased incidence and severity of Rhizoctonia] — if talking about the whole Red River Valley — is soybeans,” says Allan Cattanach, general agronomist for American Crystal Sugar Company. “Whereas corn and soybeans together probably make it worse in Southern Minn, Minn-Dak and the southern end of the Crystal growing area.”