Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 3, 1999
Publication Date: May 1, 2000
Citation: GARDNER, D.R., Pfister, J.A. LATE SEASON TOXIC ALKALOID CONCENTRATIONS IN TALL LARKSPUR (DELPHINIUM SPP.). JOURNAL OF RANGE MANAGEMENT. 2000. Interpretive Summary: Tall larkspurs (Delphinium barbeyi, D. occidentale, D. glaucescens, D. glaucum) are toxic plants that are often fatally ingested by cattle on western rangelands. Information on late-season toxicity is necessary for livestock producers to determine when the risk of poisoning is sufficiently low to allow grazing. In this study we provide information for toxic alkaloid concentrations in seed pods and leaves from the pod stage of growth to senescence at various locations in the western U.S. Leaves and pods of D. barbeyi during the pod stage at the various locations contained 2 to 3 mg/g, indicating that poisoning risk is generally low once pods have lost their green color. Although D. glaucum is the most toxic tall larkspur early in the growing season, toxicity declined rapidly once pods began to develop. D. occidentale pods were sufficiently toxic (near 4 mg/g) before maturation to pose significant risk to grazing cattle. Moderate risk persisted until seed shatter and toxicity declined to 1 to 2 mg/g. More than 70% of the D. glaucescens pod samples that we collected had toxic alkaloid concentrations above 3 mg/g (0=6.1 mg/g), whereas about 4% of the leaf samples contained more than 3 mg/g. Ranchers with cattle grazing on rangelands with populations of D. glaucescens must exercise caution throughout the entire grazing season.
Technical Abstract: Tall larkspurs [Delphinium barbeyi, D. occidentale, D. glaucescens, D. glaucum] pose a serious poisoning threat to cattle on many summer ranges. Livestock producers often defer grazing until larkspur is mature, but specific information is lacking on toxic alkaloid concentrations in larkspur from the pod stage to senescence. Tall larkspur leaves and seed pods were collected about every 2 weeks during the pod stage to senescence from marked plants in locations in Utah (Logan and Salina), Idaho (Ashton, Humphrey, and Oakley), Colorado (Yampa and Montrose), and California (Carson Pass) from 1995 to 1997. Toxic alkaloid concentrations in pods (0=2.9 mg/g) exceeded leaf alkaloid concentrations (0=1.5 mg/g) in all species, but the magnitude of the difference varied among the 4 species. Leaves showed a more rapid decrease in toxic alkaloid concentration with plant maturity compared to pods. Seed pods did not begin to lose substantial amounts of toxic alkaloid until larkspur matured and pods began to dessicate. At seed shatter, D. glaucescens pods retained more toxic alkaloid than the other species, and alkaloid concentration was sufficiently high after pods had shattered (3.5 mg/g) to pose a moderate grazing risk. After seed shatter, the toxic alkaloid concentrations in leaves and pods of D. barbeyi, D. occidentale, and D. glaucum were generally less than 2 mg/g; thus, risk of losing cattle would be low for the remainder of the grazing season.