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United States Department of Agriculture

Agricultural Research Service

Title: Locoweed Population Cycles

Authors
item Ralphs, Michael
item Pfister, James
item Welsh, Stan - BYU
item Graham, J - UNION COUNTY EXTENSION
item Purvines, J - NMSU
item Jensen, Don - USU
item James, Lynn

Submitted to: Rangelands
Publication Type: Popular Publication
Publication Acceptance Date: June 1, 2003
Publication Date: October 1, 2003
Citation: RALPHS, M.H., PFISTER, J.A., WELSH, S.L., JENSEN, D.T. LOCOWEED POPULATION CYCLES. 2002. 25(5) pp. 14-18, 25th Anniversary.

Interpretive Summary: Locoweed populations cycle and livestock losses follow theses cycles. Three survival strategies are described. Annual plants avoid drought by seed dormancy and germinate in years when sufficient moisture is available. Biennial or short-lived perennial locoweeds germinate, grow and flower when moisture is adequate. They may remain for 1 or 2 years until the next drought occurs. Long-lived perennial locoweeds grow where moisture is more abundant and regularly available. However, they too may die out during extended droughts. Ranchers should anticipate outbreaks of annual and short-lived perennial locoweeds in wet years. If outbreaks materialize, they should move their livestock to other non-infested sites to prevent poisoning. For the long-lived species, management strategies should be devised to avoid the critical times in spring and fall when the locoweed is relatively more palatable than the dormant warm season grasses.

Technical Abstract: Locoweed poisoning (Astragalus and Oxytropis spp.) is the most wide spread poisonous plant problem on western rangelands. However, livestock poisoning is erratic due to the cyclic nature of locoweed populations. Locoweeds have three genetically based survival strategies that are determined by long-term climatic cycles and short-term weather conditions. Annual plants avoid drought by seed dormancy and germinate in years when sufficient moisture is available (A. wootoni, A. emoryanus). Biennial or short-lived perennial locoweeds germinate, grow and flower when moisture is adequate. They may remain for 1 or 2 years until the next drought occurs (A. lentiginosus, A. pubentissimus, A. amphioxyx, A. mollissimus). Long-lived perennial locoweeds grow where moisture is more abundant and regularly available. However, they too may die out during extended droughts (O. sericea). Ranchers should anticipate outbreaks of annual and short-lived perennial locoweeds in wet years. If outbreaks materialize, they should move their livestock to other non-infested sites to prevent poisoning. For the long-lived species, management strategies should be devised to avoid the critical times in spring and fall when the locoweed is relatively more palatable than the dormant warm season grasses.

Last Modified: 8/22/2014
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