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

Tall larkspurs [Delphinium barbeyi (L. Huth), D. occidentale (Wats.), D. gl aucescens (Rydb.), D. glaucum (Wats.)] pose a serious poisoning threat to c attle on many summer ranges. Livestock producers often defer grazing until larkspur is mature, but specific information is lacking on toxic alkaloid c oncentrations in larkspur from pod stage to senescence. Tall larkspur leave s 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), Idah o (Ashton, Humphrey, and Oakley), Colorado (Yampa and Montrose), and Califo rnia (Carson Pass) from 1995 to 1997. Toxic alkaloid concentions in pods (( x) over bar = 2.9 mg/g) exceeded leaf alkaloid concentrations ((x) over bar = 1.5 mg/g in all species, but the magnitude of the difference varied amon g the 4 species. Leaves showed a more rapid decrease in toxic alkaloid conc entration 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 toxi c alkaloid than the other species, and alkaloid concentration was sufficien tly high after pods had shattered (3.5 mg/g) to pose a moderate grazing ris k. After seed shatter, the toxic alkaloid concentrations in leaves and pods of D. barbeyi, D. occidentale, and D. glaucum were generally less than 2 m g/g; thus, risk of losing cattle would be low for the remainder of the graz ing season.