Leafy Spurge and Grass Response to Picloram and Intensive Grazing

Abstract

More information about the effects of combining intensive livestock grazing of noxious weeds and associated desirable plants with other control measures is needed to develop effective rangeland weed management strategies. We studied the response of leafy spurge (Euphorbia esula L.) and Kentucky bluegrass (Poa pratensis L.) to intensive short-duration grazing by either sheep or cattle, in combination with picloram (4-amino-3,5,6-trichloropicolinic acid) for 5 years. In the first year, 2 pastures (16 and 24-ha) were split into 3 blocks and picloram was applied to one-half of each block at a rate of 0.9 kg ha-1. Exclosures were established to include both treated and untreated portions in each block. The smaller and larger pastures were grazed by sheep and cattle, respectively. There were 1 or 2 grazing periods per year, varying from 1- to 2-days in length. Leafy spurge stem densities were counted annually, and grass cover and plant biomass were also examined. Data from each pasture (cattle or sheep) were analyzed separately using analyses of variance. Leafy spurge was selectively grazed by sheep, and stem densities were reduced by sheep grazing (P < 0.01). Cattle did not utilize leafy spurge and stem densities were not affected. Picloram reduced leafy spurge stem densities throughout the study in both the sheep (P < 0.001) and cattle (P < 0.001) pastures. Picloram also reduced leafy spurge biomass in the sheep pasture (P < 0.05), which allowed an increase in Kentucky bluegrass biomass. Grazing X picloram interactions affecting either leafy spurge stem densities or leafy spurge biomass were not detected. An integrated leafy spurge management system may require a longer time frame, additional control measures, and (or) more intensive grazing management.