Brush Control with Herbicides on Hill Pasture Sites in Southern Oregon

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Abstract
Silvex alone or with 2,4-D in a 1:1 ratio at about 3-4 kg/ha gave 60-100% control of many brush species including poison oak [Rhus diversiloba], Oregon oak [Quercus kelloggii] and maples [Acer spp.]. Picloram at 1 kg/ha plus 2,4-D at 4 kg/ha was most effective with respect to the amount of picloram; however, the mixture of 1 kg/ha plus 2 kg/ha respectively, was nearly as good. Complete pasture renovation in this area requires brush control, burning, fertilization and seeding of desirable species. Picloram and 2,4-D disappear from soils in 29 mo. with no significant leaching into the soil profile at these study sites. Herbicide discharge in streamflow was small, representing 0.35% and 0.014% of applied picloram and 2,4-D. Nearly all of the herbicide discharged from these watersheds represents residue deposited in dry stream channels or that mobilized by fall rains from adjacent streambanks. Significant overland movement of herbicides from upslope did not occur on these study areas. The probability of crop damage from irrigation with water from these watersheds is low.