By O. Nehers and C. M. Ocamb
Cause A virus (beet necrotic yellow vein virus) transmitted by a fungus (Polymyxa betae) commonly found in soil. The disease was first detected in Idaho, Wyoming, and Nebraska in 1992. Infection often begins in low areas where soil moisture is high. Root yield and sucrose content may be drastically reduced in infected plants. The fungal-like vector may survive in infested soil 10 years or more without significant loss in viability. Anything that moves soil (farm equipment, people, irrigation water, tare dirt, wind, livestock and other animals) can spread the disease.
Symptoms Rhizomania literally means "root madness" or "crazy root." Diseased plants usually are grouped in spots or areas as well as scattered throughout the field. Root symptoms include a mass of fine, hairy, mostly dead roots surrounding the taproot. As the plant ages, primarily crown tissue continues to grow while the taproot does not, giving the root a large crown and a wineglass shape. Root proliferation gives it a bearded appearance. Vascular rings darken, and, in longitudinal section, darkened vascular tissue is somewhat translucent. Late-season infections may be more difficult to recognize because the fungus infects only young roots. Lateral roots may have only a tuft of fine-hair roots, and the only discoloration is in the lateral root's vascular system where the infection is. Foliage symptoms may include general chlorosis (fluorescent bright green-yellow color), elongated leaf shape, and erect leaf growth resembling nitrogen deficiency. Erect and chlorotic leaves can be seen above normal canopy. In addition, wilting without foliage discoloration and stunted growth can sometimes be observed. Rarely, plants may show pronounced veinal chlorosis (yellowing) and necrosis.
Cultural control
- Clean anything that moves soil such as farm equipment, people, irrigation water, tare dirt, and livestock, if possible.
- Varieties adapted to the Pacific Northwest having multi-source rhizomania resistance should be planted to minimize increase in soil inoculum. Planting resistant varieties on a minimum 4-year rotation, along with avoiding soil moisture wetter than -40 centibars (cbars) can result in good yields.
- Maintain good weed control in rotation crops.
- Prevent soil compaction and maintain good drainage.
Reference Harveson, R.M., Hanson, L.E., and Hein, G.L. 2009. Compendium of Beet Diseases and Insects. 2nd Edition. St. Paul, MN: APS Press.