Crown and Root Rots (fungi – Rhizoctonia spp., Fusarium spp., Phoma sp., Phytophthora sp., Sclerotium rolfsii, Phythium sp., and several others): Crown rot and root rot appear as a wilting of leaves followed quickly by death. Roots have dark rotted areas and develop a strong odor in some cases. The rot starts at injured sides and at the crown. Disease is worse when plants suffer from water stress during the growing season. Control is accomplished through long rotations and proper use of fertilizer and irrigation to maintain uniform moisture.
Powdery Mildew (fungus – Erysiphe polygoni): This disease first appeared in 1974 on the Texas High Plains. A white powdery growth develops on the leaf surface. Severe infection causes reduced yield and decreased sugar content. Control by regular spray programs using fungicides.
Leaf Spot (fungus – Cercospora beticola): First symptoms are small, whitish spots scattered over the surface of older leaves. The spots increase in size, becoming brownish or purplish in color. Individual spots are usually circular but several may coalesce into larger areas of dead tissue. Mature spots, about 1/4-inch in diameter, become gray as the fungus produces spores. Leaves may become yellow and die. As leaves die, the crown becomes cone-shaped with a rosette of dead leaves at the base. The fungus overwinters on dead leaves and attacks other beets, lambsquarter and mallow. The disease develops rapidly when day temperature is 80 to 90oF. High humidity and a susceptible variety are conducive to severe epidemics. Control is accomplished through long rotations, resistant varieties and through preventive fungicide applications.
Other Diseases: Curly-top virus is a serious problem on sugar beet. (See separate section on curly-top. Nematodes cause serious losses in other beet production areas. Nematode control is also discussed separately.
Phoma Leaf Spot (fungus – Phoma betae): This fungus is common in early season and where sugar beets are grown, occuring mainly on older leaves. Phoma leaf spot is of little economic importance. Symptoms are light brown leaf spots about 1 inch in diameter, with darker concentric rings. Phoma is usually controlled by foliar applications for other fungi.