ARS | Publication request: Mycoleptodiscus Crown and Root Rot of Alfalfa: An Emerging Problem in Minnesota and Wisconsin?

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: November 12, 2009
Publication Date: December 1, 2009
Citation: Samac, D.A. 2009. Mycoleptodiscus Crown and Root Rot of Alfalfa: An Emerging Problem in Minnesota and Wisconsin? Forage Focus. December issue. p. 4.

Technical Abstract: Mycoleptodiscus crown and root rot was observed on alfalfa plants from southeastern MN and southwestern WI during the summer of 2009. The disease was observed in new plantings and established stands. Although the disease has been known since the 1950's, it has not caused severe problems in alfalfa production fields. Symptoms consist of patches of plants that are stunted and yellowed with poor forage production. Plants from these patches have few lateral and fibrous roots and the remaining lateral roots may be black and rotted. Crown branches may be rotted off, leaving one to a few areas for shoot production. In the interior of the crown, brown decayed material extends from the crown into the taproot. The margin of the rotted area is often black. The black margin and presence of black sclerotia (resting structures) in the root and on the surface of the rotted crown is diagnostic. Symptoms will likely be more visible during mid- to late-summer months as the pathogen grows well at higher temperatures. The fungus causing the disease is highly pathogenic on many legumes including birdsfoot trefoil, white clover, alsike clover, red clover, crimson clover, and soybean, as well as alfalfa. No disease management measures have been reported. At this point there are no known resistant alfalfa cultivars. Maize and small grain crops are not hosts for the fungus, so crop rotation may be useful. However, sclerotia are known to be long-lived and may persist over many seasons in the soil.