Submitted to: Biochemical Systematics and Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2001
Publication Date: January 30, 2002
Citation: PFISTER, J.A., RALPHS, M.H., GARDNER, D.R., STEGELMEIER, B.L., MANNERS, G.D., PANTER, K.E., LEE, S.T. MANAGEMENT OF THREE TOXIC DELPHINIUM SPECIES BASED ON ALKALOID CONCENTRATIONS. BIOCHEMICAL SYSTEMATICS AND ECOLOGY. 2002. Interpretive Summary: This paper reviewed the use of toxic alkaloid concentrations to make management recommendations for tall larkspur (Delphinium) species. Alkaloid concentrations in tall larkspurs in excess of 3 mg/g increase risk to grazing cattle if enough larkspur is consumed. D. glaucum is most toxic and cattle should be denied access to dense patches throughout the grazing season until after seed shatter. Toxic alkaloid levels in D. barbeyi are highest in immature plants, but D. barbeyi is unpalatable to cattle until the early flower stage. Livestock producers can take advantage of cattle diet selection patterns for D. barbeyi by grazing these ranges early in the season when it is not palatable, then removing cattle from early flowering stage through mid-pod stage when cattle are most likely to be poisoned. During the late summer and early fall, cattle can again safely graze D. barbeyi when the toxic alkaloid concentration declines below 3 mg/g. Cattle losses from D. occidentale are usually less severe than from D. barbeyi, but generally the same recommendations apply as for D. barbeyi. Sampling tall larkspurs to determine alkaloid concentrations is an essential management tool. Tall larkspur populations can be tested for toxicity throughout the growing season. Whenever toxic alkaloid concentrations exceed 3 mg/g in leaves, flowers, or pods, cattle should be removed from the pasture and not returned until pods begin to shatter and risk of poisoning is lower. Tall larkspur are safe to graze when alkaloid concentrations fall below 3 mg/g because it is difficult for cattle to eat sufficient larkspur to become fatally poisoned.
Technical Abstract: A systematic approach to the taxonomic classification of the tall larkspur complex (Delphinium spp.) has been developed and implemented using molecular genetics, plant morphology, and alkaloid profiles, as shown in other papers in this series. This approach supports the classification of three distinct species (D. glaucum, D. barbeyi and D. occidentale), as the species differ in genetics and toxicity. Toxic alkaloid concentrations over the growing season were integrated with data on diet selection to make management recommendations on a species-specific basis to reduce the risk of poisoning cattle. Alkaloid concentrations in tall larkspurs in excess of 3 mg/g impart moderate or high risk to grazing cattle if sufficient quantities are consumed. D. glaucum is most toxic, with toxic alkaloid concentrations that exceed 3 mg/g throughout the grazing season until late maturity. Cattle should be denied access to dense patches of this species throughout the grazing season until after seed shatter. Concentration of toxic alkaloids in D. barbeyi is highest in vegetative plants, but D. barbeyi is unpalatable to cattle until flowering racemes begin to elongate. We recommend grazing D. barbeyi ranges early in the season when it is not palatable, then removing cattle from early flowering stage through mid-pod stage when cattle are most likely to be poisoned. Cattle can again safely graze D. barbeyi late in the season when the toxic alkaloid concentration typically declines below 3 mg/g. Some populations of D. occidentale and the D. barbeyi x D. occidentale hybrids do not contain toxic alkaloids, and pose little risk of poisoning throughout the year. Toxicity of northern populations of D. occidentale varies from year-to-year for unknown reasons. Cattle losses from D. occidentale are usually less severe than from D.