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The Influence of Irrigation Frequency and Cultivar Blends on the Severity of Multiple Root Diseases in Sugar Beets

The effects of cultivar mixtures and two irrigation frequency treatments were evaluated over two seasons for their impact on a complex of sugar beet root diseases in three fields infested with the fungal pathogens Aphanomyces cochliodes, Fusarium oxysporum f. sp. radicis-betae, Rhizoctonia solani, and the viral pathogen Beet necrotic yellow vein virus (BNYVV). Irrigations after emergence consisted of two or five (two 1994 studies) and three or six (1995 study) applications of water for dry and wet treatments, respectively. Cultivar treatments included MH9155, HH67, Ranger, Rhizosen, and four combinations of these same cultivars. Disease progress was monitored through destructive sampling of plants exhibiting foliar symptoms typical of root disease during the season. At harvest, data on root and sucrose yields, sucrose percentage, and a root disease index were collected. No significant irrigation × cultivar treatment interactions were observed. Few significant differences were observed between irrigation treatments involving measured yield components. Reduced irrigations however, resulted in significantly lower disease incidence in all three repeated experiments when cultivar treatments were combined. No added benefits were observed for increasing yield or decreasing root disease by planting mixed cultivars, compared to the same cultivars planted individually. Several regionally adapted cultivars performed as well or better than mixtures under the unusually high levels of disease pressure in test fields. When few alternative options are available, sugar beet growers may still benefit from reducing irrigations, and growing locally adapted cultivars in soils severely infested with root pathogens.