Submitted to: Poisonous Plants Symposium Proceedings
Publication Type: Book / Chapter
Publication Acceptance Date: May 20, 2003
Publication Date: November 1, 2003
Citation: Ralphs, M.H., Gardner, D.R., Pfister, J.A. 2003. Toxicophenology and grazing risk models of tall larkspur. Poisonous Plants Symposium Proceedings. Interpretive Summary: Tall larkspurs are the most important poisonous plant problem on mountain rangelands in the western U.S. Toxic alkaloid concentration declines in a curvilinear trend as it matures. Alkaloids are synthesized in the first 3- 4 weeks of growth. Thereafter, a constant amount of alkaloid is diluted as the plant continues to grow and increase in size and biomass. Regression models were developed to predict toxicity of larkspur populations. Conceptual models were developed to identify a toxic window when risk of poisoning is greatest.
Technical Abstract: Tall larkspus (Delphinium barbeyi, D. occidentale, D. glaucum) are the most important poisonous plant problems on mountain rangelands in the western U.S. They are palatable to livestock and acutely toxic to cattle. Cattle deaths average 2 to 5% on mountain rangelands, but may exceed 15% in areas where larkspurs are abundant (Pfister et al., 1999). In addition to cattle edeaths, significant amounts of forage are wasted and management costs increase as producers defer or avoid grazing larkspur-infested areas. Total cost to the livestock industry exceed $40 million annually. Larkspur plants contain many norditerpenoid alkaloids. Alakloids containing the N-(methylsuccinimido)-anthranilic ester group (MSAL) are most toxic, with methyllycaconitine (MLA) being the most prominent (Manners et al., 1995) (Figure 1). MLA is a potent neuromuscular blocker, causing paralysis and rapid death from respiratory failure (Dobelis et al., 1999).