Cause Rhizoctonia solani is a fungus that has a broad host range and survives primarily as mycelium or sclerotia in plant debris. Rhizoctonia solani becomes active when soil is 77°F to 91°F, attacking any part of the plant in contact with soil. The fungus is favored by poor soil structure and high soil moisture. Infections can move plant-to-plant, creating diseased "pockets" in a field.
Symptoms Black lesions are present on the crown and lower petioles. Severely infected fleshy roots may have large regions of dry rot, dark brown to black in color.
Cultural control The most effective management is to promote good crop growth and avoid plant stress.
- Do not plant beet crops consecutively. A 3-year rotation is the minimum; lengthen to 4 to 5 years if root rot is a problem. Shortened rotations in affected fields are associated with increased losses and a build-up of pathogen populations that make future control more difficult.
- Practice a 3-year rotation with non-host crops (grains).
- Control soil compaction.
- Amplitude at 3.2 to 4.8 fl oz/100 lb seed pieces, 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, or 3 to 4 quarts/A as a chemigation treatment on 14- to 21-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, 3 to 4 quarts/A as a soil drench on 10- to 14-day intervals, or 3 to 4 quarts/A as a chemigation drip treatment on 14- to 21-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
Reference Harveson, R.M., Hanson, L.E., and Hein, G.L. 2009. Compendium of Beet Diseases and Pests, 2nd Ed. St. Paul, MN: APS Press.