LEAFY SPURGE AND GRASS RESPONSE TO PICLORAM AND INTENSIVE GRAZING

More information about the effects of combining intensive livestock gr azing of noxious weeds and associated desirable plants with other cont rol measures is needed to develop effective rangeland weed management strategies. We studied the response of leafy spurge (Euphorbia esula L .) and Kentucky bluegrass (Pea pratensis L.) to intensive short-durati on 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 app lied 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 eac h block. The smaller and larger pastures were grazed by sheep and catt le, 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 f rom each pasture (cattle or sheep) were analyzed separately using anal yses of variance. Leafy spurge was selectively grazed by sheep, and st em densities were reduced by sheep grazing (P<0.01). Cattle did not ut ilize leafy spurge and stem densities were not affected. Picloram redu ced 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 increas e in Kentucky bluegrass biomass. Grazing x picloram interactions affec ting either leafy spurge stem densities or leafy spurge biomass were n ot detected. An integrated leafy spurge management system may require a longer time frame, additional control measures, and (or) more intens ive grazing management.