|Johnson, David - MICHIGAN ST UNIVERSITY|
Submitted to: Annual Beet Sugar Development Foundation Research Report
Publication Type: Other
Publication Acceptance Date: May 26, 2000
Publication Date: N/A
Technical Abstract: Seedling diseases of sugarbeets cause production losses in Michigan, however, the identities of pathogens causing this disease are not known. A survey of diseased seedlings and of field soils was initiated in 1999 to determine the identities of these pathogens and their roles in reducing sugarbeet stands. Field soils and diseased seedlings were collected in April, May, and June. Pathogens were isolated from diseased seedlings and identified. Seeds were planted in pots of field soils, and pathogens causing disease of germinated seedlings were isolated and identified. Isolates of the pathogen Pythium spp. were evaluated for tolerance to the fungicide metalaxyl, a chemical used on all sugarbeet seeds in Michigan for control of Pythium. Pythium spp. were the most frequently isolated pathogens in early seedling samples, and Rhizoctonia solani was the most frequently isolated pathogen late in the planting season. Other pathogens isolated throughout the planting season included Phoma betae and Aphanomyces cochlioides. Pythium spp. were the pathogens most frequently isolated from soil samples. Several of the Pythium isolates were resistant to the fungicide metalaxyl, and these isolates also were among the most virulent pathogens of those tested. We recommend future assessment of new fungicides and formulations that may provide better control of Pythium spp. than those currently used. Past efforts to control seedling diseases of sugarbeets in Michigan have focused on control of Aphanomyces cochlioides. Future efforts may better be directed toward control of Pythium spp. and Rhizoctonia solani.