|Holen, Doug -|
Submitted to: Extension Publications
Publication Type: Other
Publication Acceptance Date: May 15, 2010
Publication Date: May 15, 2010
Citation: Holen, D., Samac, D.A. 2010. Dig Alfalfa Plants to Assess Root Rots and Yield Potential. Forage Quarterly. 4:2. Technical Abstract: Digging alfalfa plants and inspecting their crowns and roots for rot is critical to assess stand health and production potential. Brown root rot (BRR) has been a significant plant disease on alfalfa for decades but until recently was thought to only cause significant damage in western Canada. With improved lab testing procedures and more sampling, the disease is now known to be in the U.S. BRR has been identified in alfalfa fields in 13 States within 3 regions: 1) the Intermountain West, 2) MN and WI, and 3) the Northeast. The pathogen is relatively widespread across MN, with BRR confirmed in about 18 counties from northwest to southeast MN. With favorable conditions, considerable inoculum, and a susceptible host, substantial stand and production losses are possible. Damage can occur gradually or during a single winter. Management of BRR includes practices that ensure healthy plants going into winter. Fertility and harvest management maximize production and limit the disease. Crop rotation is beneficial but difficult since corn, soybean, and other legume and grass species are either hosts or their residue allows fungal colonization over winter. Spring-sown small grains are among the best rotation options to reduce the pathogen's population. A 'new' alfalfa disease called Mycoleptodiscus crown and root rot (MCRR) was identified in MN in 2009. This disease causes stand decline in summer. However, plants infected last year have been showing decline this spring. The disease has been found in southeastern MN, it is suspected to be Statewide. Symptoms of BRR and MCRR are somewhat similar. However, BRR causes plant decline primarily in spring with symptoms mostly on roots, while MCRR causes decline mostly in the summer with symptoms mostly on crowns. Scout alfalfa fields often to monitor yield-limiting stand issues. Once detected, invest the time to identify the cause(s). BRR can be confused with Phytophthora root rot, insect root grazing, or climatic winterkill. A lab test is needed to accurately diagnose BRR. After a condition is diagnosed, appropriate management strategies can be implemented.