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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #242732

Title: Brown Root Rot of Alfalfa

item HOLLINGSWORTH, CHARLA - University Of Minnesota
item Samac, Deborah - Debby
item PETERSON, PAUL - University Of Minnesota
item HOLEN, DOUG - University Of Minnesota
item PERSON, HOWARD - University Of Minnesota

Submitted to: Extension Service Bulletins
Publication Type: Other
Publication Acceptance Date: 7/24/2009
Publication Date: 8/1/2009
Citation: Hollingsworth, C., Samac, D.A., Peterson, P., Holen, D., Person, H. 2009. Brown Root Rot of Alfalfa. University of Minnesota Extension Service Bulletin. 4 p.

Interpretive Summary:

Technical Abstract: This bulletin describes the disease of alfalfa called brown root rot (BRR) including: the disease symptoms, the fungal pathogen and its biology, its distribution, and disease management. Since the 1920s, BRR has been regarded as an important disease of forage legumes, including alfalfa, in northern regions of the North American continent. Until recently the disease was labor-intensive and time-consuming to diagnose. To overcome these difficulties, a lab assay was developed to detect and quantify the pathogen from plant and soil samples. BRR has now been reported from northeast locations such as New York, Maine, Pennsylvania, Vermont, New Hampshire, and Ontario, Canada, as well as high-altitude locations in Colorado and New Mexico. The pathogen is widespread through Minnesota and Wisconsin. The pathogen is relatively dormant during the summer when soil temperatures are warm and other soil-borne pathogens are most active. The pathogen requires cool soil temperatures in which to cause disease. Moreover, it is described as a "snow mold" because its growth is most rapid when soils are covered by snow. If disease development is promoted, substantial stand loss can occur. Such losses can either result during a single winter season or can take place gradually over a number of years. Roots of severely diseased plants can have darkened root lesions from the crown-root junction and below. Root rot is common on diseased tap, lateral, and feeder roots, as well as on nodule tissues. Lesions are medium to dark brown and sometimes, but not always, have a thin, darker band around their perimeter. Disease management strategies are limited for soil-borne pathogens. Overall, producers should focus on maintaining good plant health, particularly as the growing season draws to a close. Similar to other disease issues, an integrated management approach is the best strategy to minimize the effects of BRR. Rotating with spring-sown small grain crops such as oat, barley, and wheat reduces inoculum levels, as does fallowing the field. Several commercial alfalfa varieties show good stand persistence in locations with BRR pressure.