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Aphanomyces Damping-off and Root Rot of Sugarbeet (05/23/19)

During wet and warm conditions, sugarbeet may be affected by Aphanomyces root rot caused by the pathogen Aphanomyces cochlioides.

During wet and warm conditions, sugarbeet may be affected by Aphanomyces root rot caused by the pathogen Aphanomyces cochlioides. The disease is most damaging in wet soils at temperatures of 68 to 86°F. Aphanomyces can be deadly in the seedling stage, and can cause serious root rot later in the season. Infected seedlings typically have roots and hypocotyls that become black and shrink to a dark, slender thread. Infected plants have light green leaves with older leaves becoming yellow. Plants tend to wilt in the afternoons of hot, dry, and sunny days. Field assessment should therefore be done in the afternoons of hot sunny days. Fields of surviving plants with severe root infections have reduced root yield, lower sucrose content, and higher impurities. During defoliation, many of the infected roots are knocked out of the soil and are not harvested. Diseased roots have much higher respiration rates compared to healthy roots. Consequently, the quality of beets in storage piles is reduced when diseased roots are stored with healthy roots.

Plant Aphanomyces tolerant varieties in fields with a history of this disease. Many high yielding Aphanomyces tolerant varieties are available. For additional protection for fields with a history of the disease, seeds should be treated with Tachigaren. Planting done early in the season facilitates early and vigorous growth in conditions unfavorable to the pathogen. Field drainage should be improved since the pathogen needs adequate free moisture to germinate and cause infections. Fields with a history of severe Aphanomyces should be treated with about 7 to 10 tons of factory-spent lime per acre. Research shows that plots treated with spent lime results in a significant reduction in Aphanomyces root rot, and higher recoverable sucrose yield, the lime does not adversely impact other crops in the rotation, and the benefits are realized for over 12 years. Effective control of weeds, such as lambsquarters, pigweed and kochia, which serve as host to A. cochlioides, also helps to reduce the pathogen’s population.

Mohamed Khan

Extension Sugarbeet Specialist

NDSU & U of MN

701-231-8596

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