Lack of Herbicide Effect on Severity of Aphanomyces Root Rot of Sugarbeet

Nearly all sugarbeet fields in Minnesota and eastern North Dakota are treated with herbicides. Many of these fields are infested with Aphanomyces cocitlioides, a soilborne pathogen that has increased in prevalence and severity in the region during unusually wet growing seasons in the 1990s. Trials were conducted in four fields naturally infested with A. cochlioides to determine if herbicides commonly applied before planting and after emergence affected stand loss and root rot caused by the pathogen. Herbicides applied and incorporated into soil before planting (cycIoate, diethatyl, EPTC, ethofumesate) and those applied after emergence (cIopyralid, desmedipham, desmed­ ipham + phenmedipham, triflusulfuron) did not affect severity of disease caused by A. cochlioides compared to a hand-weeded control.