THE EFFECT OF SPENT LIME ON SUGARBEET YIELD AND APHANOMYCES COCHLIOIDES SUPPRESSION

Aphanomyces root rot and black root in sugarbeet seedlings caused by the fungus Aphanomyces cochlioides is becoming more prevalent in the Red River Valley of North Dakota and Minnesota, southern Minnesota and other sugarbeet growing regions of the world. Warmer temperatures, higher than normal precipitation and crop rotation practices are causing an increase in A. cochlioides populations and sugarbeet infection (Adams, 1991). Sugarbeet stand and yield are reduced due to the above factors resulting in lost revenue for the grower. A. cochlioides is an oomycete whose infective unit is a zoospore. Water saturated soil is necessary for production, movement and germination of the zoospore within the soil profile (Rush and Vaughn, 1993). Moisture allows zoospores to migrate to the sugarbeet root system resulting in infection. Dryer soil will leave the zoospore virtually immobile and less likely to cause disease. During infection the hydrolytic enzymes produced by the fungus cause cell collapse allowing the fungus to spread more rapidly in the sugarbeet tissue (Papavizas and Ayers, 1974). Management strategies previously used for this disease have included seed treatment, development of resistant cultivars, enhanced drainage, controlling weed hosts and crop rotation.