Dalmatian toadflax and geyer larkspur management through targeted grazing and herbicide

Targeted grazing and herbicides are two rangeland weed control tools. Using a series of greenhouse and field studies, we evaluated effectiveness of both for controlling the invasive perennial forb Dalmatian toadflax (Linaria dalmatica). Defoliating toadflax (removing its leaves) reduced regrowth more than pruning (clipping stems). Sheep, whose toadflax browsing pattern typically defoliates, limited toadflax stem density increase in a field setting when grazed in spring and summer 2014 and 2015. Grazing also reduced Geyer larkspur (Delphinium geyeri), a species toxic to cattle, but immediate reductions in perennial grass biomass limited applicability of our treatments for same-season cattle grazing. The herbicide treatment chlorsulfuron + aminocyclopyrachlor provided best residual toadflax and larkspur control in both field studies, but metsulfuron + aminopyralid and fall-applied chlorsulfuron showed comparable second year results with less non-target species impact. Early November herbicide applications controlled toadflax better and with fewer non-target impacts than mid-June herbicide treatments.