Locoweed toxicity, ecology, control and management

Authors: Ralphs, Michael; Stegelmeier, Bryan

Submitted to: International Journal of Poisonous Plant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2011
Publication Date: 11/15/2011
Citation: Ralphs, M.H., Stegelmeier, B.L. 2011. Locoweed toxicity, ecology, control and management. International Journal of Poisonous Plant Research. 1(1):47-64.

Interpretive Summary: Locoweed is the most widespread poisonous plant problem in the western U.S. The toxic alkaloid swainsonine is produced by the endophyte (Undifillum oxytropis). It inhibits several key mannosidase enzymes of lysosomal and glycoprotein metabolism, resulting in abortions and reduced fertility of both sexes, neurological disturbances ranging from extreme depression to aggression, compromised immune system resulting in increased disease, and impaired ability to eat or drink leading to weight loss and eventual starvation. Populations of almost all locoweed species cycle; increasing in wet years and die back during drought. Locoweeds are relatively palatable during some seasons of the year. The most effective management strategy to prevent poisoning is to deny livestock access to locoweeds during critical periods when they are more palatable than associated forage. Reserving locoweed-free pastures or controlling existing locoweed populations with herbicides can provide "safe" pastures for critical periods. Good range management and wise grazing strategies can provide adequate forage for livestock and avoid grazing locoweed during critical periods when it is palatable.

Technical Abstract: Locoweed is the most widespread poisonous plant problem in the western U.S. Some species of Astragalus and Oxytropis contain the indolizidine alkaloid swainsonine which causes the poisoning syndrome known as locoism. Swainsonine is produced by the endophyte (Undifillum oxytropis). It inhibits several key mannosidase enzymes of lysosomal and glycoprotein metabolism, resulting in buildup of unmetabolizable sugars, disrupted hormone and enzyme synthesis and altered receptor binding. Nearly all body systems are adversely affected. Populations of almost all species cycle; increasing in wet years and die back during drought. Locoweeds are relatively palatable compared to the alternative forages during some seasons of the year. The most effective management strategy to prevent poisoning is to deny livestock access to locoweeds during critical periods when they are more palatable than associated forage. Reserving locoweed-free pastures or controlling existing locoweed populations with herbicides can provide "safe" pastures for critical periods. Good range management and wise grazing strategies can provide adequate forage for livestock and avoid critical periods of the year.