• Late season toxic alkaloid concentrations in tall larkspur (Delphinium spp.)

      Gardner, D. R.; Pfister, J. A. (Society for Range Management, 2000-05-01)
      Tall larkspurs [Delphinium barbeyi (L. Huth), D. occidentale (Wats.), D. glaucescens (Rydb.), D. glaucum (Wats.)] 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 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 concentions in pods (average= 2.9mg/g) exceeded leaf alkaloid concentrations (average= 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 generallyless than 2 mg/g; thus, risk of losing cattle would be low for the remainder of the grazing season
    • Toxic alkaloid concentration in tall larkspur species in the western U.S

      Ralphs, M. H.; Manners, G. D.; Pfister, J. A.; Gardner, D. R.; James, L. F. (Society for Range Management, 1997-09-01)
      Larkspur (Delphinium spp.) kills more cattle on mountain rangelands in the western U.S. than any other plant, disease or predator. The concentration of toxic alkaloids was measured in 4 larkspur species, at 10 locations, at 2-week intervals during the growing season. In addition, multi-year samples from previous studies were analyzed to determine year-to-year variation in toxic alkaloids. Mountain larkspur (D. glaucum Wats.) had the highest concentration of toxic alkaloids averaged over growth stages (1.01% of dry weight), tall, (D. barbeyi (L.) Huth) and waxy larkspur (D. glaucesens Rydb) were intermediate (0.65 and 0.49% respectively), and duncecap (D. occidentale S. Watts) was lowest (0.29%). Toxic alkaloid concentration generally declined as the plants matured. However, toxic alkaloids in tall larkspur at Yampa, Colo. increased slightly in the pod stage, and toxic alkaloids in waxy larkspur increased from the vegetative to the bud stage. Concentration of toxic alkaloids in tall and duncecap larkspur leaves were higher in plants growing in open sunlight than those shaded under aspen or conifer canopy. Toxic alkaloid concentration varied among individual plants (C.V. 20-60%). Knowledge of the toxic alkaloid concentration of larkspur populations can be used to predict the risk of larkspur poisoning.
    • Toxic alkaloid levels in tall larkspur (Delphinium barbeyi) in western Colorado

      Pfister, J. A.; Manners, G. D.; Gardner, D. R.; Ralphs, M. H. (Society for Range Management, 1994-09-01)
      Consumption of tall larkspur (Delphinium barbeyi L. Huth.) can be fatal to cattle grazing mountain rangeland during summer. Tall larkspur contains many alkaloids, but virtually all the toxicity is caused by methyl succidimido anthranoyl lycoctonine-type (MSAL) diterpenoid alkaloids. We measured the concentration of MSAL alkaloids (% of dry matter) in tall larkspur in various phenological stages during 1990, 1991, and 1992 near Yampa, Colorado. The site represented tall larkspur-infested rangelands on the western slope of the Rocky Mountains. Toxic alkaloid concentrations were greatest (0.4 to 0.6%) early in the growing season (bud stage). Toxic alkaloid concentrations were generally static during the flower and pod stages, or increased during the pod stage. Immature leaves had greater MSAL alkaloid concentrations early in the growing season compared to flowering parts. Alkaloid concentrations in pods were greater than in leaves (P<0.05; pod stage), as pod concentrations increased to 0.4% late in the growing season. In 2 of 3 years, plant parts did not differ in MSAL alkaloid concentrations, although weather conditions differed each year. Concentrations of toxic alkaloids did not seem to influence amounts of tall larkspur consumed by grazing cattle on the same sampling dates. Many livestock producers defer grazing of tall larkspur ranges until the plant is in the pod stage because of a general belief that toxicity is greatly reduced. Our results suggest that grazing tall larkspur ranges during the pod stage may exacerbate cattle losses if MSAL alkaloid concentrations do not decrease, yet consumption by cattle increases.