NDSU EXTENSION SERVICE

PP1247 (Revised) Fusarium Yellows of Sugar Beet Mohamed F. R. Khan Professor and Extension Sugar Beet Specialist North Dakota State University and University of Minnesota Carl A. Bradley Former Extension Plant Pathologist, North Dakota State University Carol E. Windels Retired Professor of Plant Pathology, University of Minnesota Northwest Research and Outreach Center, Crookston

Fusarium yellows of sugarbeet was identified in the Red River Valley in a few fields between

Figure 1. Lower, older leaves become yellow Moorhead, Minn., and Drayton, N.D., in 2002. Fusarium between the larger veins and eventually die but yellows is caused by the fungus Fusarium oxysporum f. sp. remain attached to the plant. betae, although other Fusarium species can be involved as secondary invaders. The disease causes significant reduction in root yield and recoverable sucrose. In storage, the quality of infected roots may deteriorate more rapidly than in noninfected roots.

■ Symptoms Fusarium yellows first appears on older leaves as chlorosis (yellowing) between the larger veins. As the disease progresses, younger leaves also become chlorotic, and the older, symptomatic leaves become necrotic (Figure 1). Occasionally, only half a leaf is chlorotic or necrotic Figure 2. Some plants infected with Fusarium may have half a leaf with necrosis. (Figure 2) (a symptom more typical of Verticillium wilt, which also was identified recently on sugar beet in this region). In the early stages of the disease, foliage tends to wilt

North Dakota State Universtiy during the day but recovers overnight. Entire leaves eventually die but remain attached to the plant and collapse in a heap around the crown. This disease has no external root symptoms. A transverse section through the root shows a grayish-brown vascular discoloration (Figures 3-5). Mature plants rarely die, but yield is reduced. Reviewed March 2018 NDSU EXTENSION SERVICE

■ Biology Fusarium oxysporum f. sp. betae survives in soil and plant residues as spores, chlamydospores or mycelium. When conditions are favorable, the fungus enters sugar beet roots and invades the vascular system, where it produces toxins that are transported upward in the plant, causing foliar symptoms. The fungus also acts as a “plug” that clogs the vascular tissue and, subsequently, causes wilting. The disease is favored by high soil temperatures — above 75 F. Symptoms typically do not appear early in the growing season. Fields that are waterlogged or have poor Figure 3. This infected root has grayish-brown to soil structure provide favorable conditions for infection. black discoloration of vascular bundles. The fungus survives in soil for many years. Nematode infection often will increase the severity of Fusarium wilt. Fortunately, nematodes have not been identified on sugar beet grown in Minnesota and eastern North Dakota.

■ Management Crop rotation may reduce inoculum buildup in the soil, but this practice is unreliable because F. oxysporum f. sp. betae has a wide host range and chlamydospores survive for many years. Movement of infested soil on contaminated field equipment should be avoided to prevent its spread to noninfested fields. Figure 4. The outer surface of an infected root shows no symptoms. A transverse section No fungicide that provides effective disease control is through the root shows grayish-brown to black discoloration. available. Growers who have fields with a history of the disease should plant Fusarium yellows-resistant varieties.

Photo credits Figures provided by C. A. Bradley, M. F. R. Khan, and R. Nelson. Selected References Duffus, J. E. and Ruppel, E. G. 1993. Diseases. Pages 346-427 In: The sugar beet crop. D. A. Cooke and R. K. Scott (Eds.) Chapman and Hall, London. Franc, G. D., Harveson, R. M., Kerr, E. D. and Jacobsen, B. J. 2001. Disease management. Page 131-160 In: Sugarbeet Production Guide. Univ. Nebraska Coop. Extension EC01-156. Schneider, C. L. and Whitney, E. D. 1986. Fusarium Yellows. Page 18 In: Compendium of Beet Diseases and Insects. E. D. Whitney and J. E. Duffus (Eds.). APS Press, St. Paul, MN.

Figure 5. This shows the disintegration of cells in the vascular tissue in an advanced stage of the For more information on this and other disease. topics, see www.ag.ndsu.edu

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