Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2000
Publication Date: January 1, 2001
Citation: Ralphs, M.H., Gardner, D.R. 2001. Influence of defoliation on toxic alkaloid concentration in tall larkspur. Journal of Chemical Ecology. Interpretive Summary: Early research suggested that defoliation reduced total alkaloid concentration in Duncecap larkspur (Delphinium occidentale). If defoliation reduces the toxicity of larkspur, clipping or mowing larkspur patches may reduce the risk of poisoning in cattle. Clipping tall larkspur (Delphinium barbeyi) at 5 cm while in the early bud stage of growth reduced dits vigor two subsequent years (i.e. number of stalks/plant and plant height). Some plants were severely stunted. Alkaloid concentration was similar to control plants, but alkaloid pools (total amount of alkaloids in larkspur stalks) were 70% lower than in control plants, due to the reduced biomass of clipped stalks. Clipping tall larkspur reduced its vigor and alkaloid pools. This may reduce the risk of poisoning to cattle.
Technical Abstract: Early research suggested that defoliation reduced total alkaloid concentration in Duncecap larkspur (Delphinium occidentale). The objective of this study was to determine if defoliation would reduce toxic alkaloid concentration and alkaloid pools in tall larkspur (D. barbeyi). The study was replicated at two locations in the mountains of central Utah. Ten uniform plants in the early bud stage (40 cm in height) were selected at each site and clipped 5 cm above the soil in 1997. In 1998, one stalk from each plant was harvested on a weekly basis; in 1999, one stalk was harvested at four points during its phonological development, to evaluate the alkaloid response to clipping over the growing season. Toxic and total alkaloid concentration were measured and alkaloid pools in the entire stalk were calculated. Clipping reduced stalk height to less than 50 cm in 1998 and 65 cm in 1999, compared to over 100 cm in unclipped control plants. Alkaloid concentration was similar to control plants, but toxic alkaloid pools in the entire stalk of clipped plants were 70% lower than in undefoliated control plants. Clipping reduced subsequent vigor and the amount of toxic and total alkaloids in tall larkspur.