Mob Grazing to Control Pasture Weeds in South Dakota.

            Mob grazing is a grazing system that uses ultra high stocking densities of 100,000 pounds per acre or more for short durations of a few hours to one day in small paddocks.  Mob grazing has been suggested to increase vegetation usage and minimize selective grazing behavior compared with lower stocking density grazing systems.  Decreased selectivity increases grazing pressure on less desirable forages, such as spiny thistles and tough, woody brush.  The objective of this project was to determine effects of mob grazing cattle on the selected invasive weeds: musk thistle (Carduus nutans), absinth wormwood (Artemisia absinthium), and buckbrush (Symphoricarpos occidentalis).  Cooperating producers in Hayti, Selby, and Chamberlain, South Dakota named their most problematic pasture weeds, listed above.  The Hayti site consisted of mob grazed, rotationally grazed, and spray/rotationally grazed treatments; Selby of rotationally grazed and mob grazed treatments; and Chamberlain of ungrazed and mob grazed treatments.  The specific problematic weed at each site was permanently tagged along transects.  Measurements of weeds and surrounding vegetation were taken before and after grazing.  Initial results quantified a decrease in weed volume and height in mob grazed pastures; a decrease in surrounding vegetation height, but not weed volume in rotational pastures; and an increase in vegetation height and weed volume for the ungrazed pasture. These data indicate that mob grazing does decrease herbivore grazing selectivity, and may be a feasible method of weed control in South Dakota grazinglands.