LONG-TERM CHANGE IN VEGETATION FOLLOWING HERBICIDE CONTROL OF LARKSPUR

Larkspur (Delphhinium spp,) control can reduce cattle deaths on mounta in rangelands, but vegetation cover must be maintained to protect wate rsheds from erosion, The objective of this study was to evaluate the l ong term impact of herbicides on larkspur control and cover of associa ted species, Duncecap larkspur (Delphinium occidentale S. Watts) near Oakley Ida., and tall larkspur (D. barbeyi Huth) near Manti Utah, were the target species. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarbo xylic acid) was applied at 1.1, 2.2, and 4.5 kg ae/ha; glyphosate (N-( phosphonomethyl)glycine) was applied at 0.06, 1.1, and 2.2 kg ai/ha; a nd metsulfuron (1-[[[[(4-methoxy-6-methyl-1,3,5-triazin- 2-yl)amine]ca rbonyl]amino]sulfonyl]benzoic acid) was applied at 0.035, 0.07, and 0. 14 kg ai/ha. Picloram at 2.2 kg/ha maintained long-term control of bot h larkspur species (> 80%) when applied in the vegetative, bud, and fl ower growth stages. Total grass cover was higher on picloram plots tha n other treatments. Forb cover declined and bare ground was greater in picloram plots than other treatments at Manti. Metsulfuron controlled dunce-cap larkspur when applied in the vegetative stage. However, lon g-term control of tall larkspur at Manti declined as new tall larkspur seedlings established, Glyphosate controlled both larkspurs when appl ied in the vegetative and bud stages, but it allowed undesirable annua l and rhizomatous forbs and shrubs to increase by the end of the study , Grass cover was lower on glyphosate plots than on other treatments. Bare ground was higher on glyphosate plots than other treatments at Oa kley, but was intermediate at Manti.