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United States Department of Agriculture

Agricultural Research Service

Title: Predicting Toxicity of Tall Larkspur (Delphinium Barbeyi): Measurement of the Variation in Alkaloid Concentration among Plants and among Years

Authors
item Ralphs, Michael
item Gardner, Dale
item Turner, D. - USDA FOREST SERVICE
item Pfister, James
item Thacker, Eric

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2002
Publication Date: November 1, 2002
Citation: Ralphs, M.H., Gardner, D.R., Turner, D.L., Pfister, J.A., Thacker, E.T. 2002. Predicting toxicity of tall larkspur (delphinium barbeyi) and measurement of the variation in toxic alkaloid concentration between plants and among yearss. Journal of Chemical Ecology. Vol. 28, No. 11 pp. 2327-2341.

Interpretive Summary: Tall larkspur (Delphinium barbeyi) is the principle mountain larkspur responsible for the majority of cattle deaths in western Colorado and central and southern Utah. The objectives' of this paper were to describe the variation in toxic alkaloid concentrations and predict toxicity. Individual larkspur plants varied in toxic alkaloid concentration, especially in early growth (14 to 38 mg/g). As the alkaloid concentration declined over the growing season, variation among plants also declined. There were yearly differences in toxic alkaloid concentration between individual plants and populations, even after accounting for differences in phonological growth between years. Toxic alkaloid concentration declined in a curvilinear manner over the growing season. Growing degree days were the best single predicator of toxic MSAL alkaloid levels: In y = (3.581 - .00423 GDD), R2 = 0.85. This predictive equation can provide a tool for ranchers and land managers to make management decisions of when to graze cattle in larkspur areas.

Technical Abstract: Tall larkspur (Delphinium barbeyi) is the principle mountain larkspur responsible for the majority of cattle deaths on mountain rangelands in western Colorado and central and southern Utah. The objective of this paper was to describe the variation in toxic alkaloid concentrations between plants, over the growing season, and among years, and to predict toxin concentrations. Ten plans in each of two tall larkspur populations in the mountains near Ferron and Salina, Utah were marked and single stalks were harvested periodically through the growing season for 4 years. Toxic alkaloid concentration was determined by Fourier Transform Infrared spectroscopy (FTIR). Individual larkspur plants varied in toxic alkaloid concentrations, especially in early growth (14 to 38 mg/g). As the alkaloid concentration declined over the growing season, variation among plants also declined. There were yearly differences in toxic alkaloid concentration between individual plants (P< 0.01) and populations (P < 0.0001), even after accounting for differences in phonological growth between years. Variables such as precipitation, temperature, days since snow melt, growing degree days (sum of mean temperature each day from snow melt), plant height and weight were all considered in a Mallows Cp multiple regression selection procedure to predict alkaloid concentration. The mixed model procedure in SAS adjusted the regression equation for locations and years. Growing degree days was the best single predictor of toxic alkaloid levels: In y = (3.581 - 0.00423 GDD), R2 = 0.85. Internal validation of this equation within the individual years and locations from which the equation was developed, produced correlations between observed vs. predicted values ranging from r = 0.73 to 0.93. External validations on nine other larkspur populations produced correlations ranging from r = 0.76 to 0.99. This predictive equation can provide a tool for ranchers and land managers to make management decisions of when to graze cattle in larkspur areas.

Last Modified: 7/22/2014
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