A study was conducted to determine the effects of five densities each of rough pigweed (Amaranthus retroflexus L.), green foxtail (Setaria viridis (L.) Beauv.), and combinations of the two upon sugar beet yields, top weights, percent sucrose, and total vegetation weights. Green foxtail was less competitive per plant than rough pigweed. Foxtail densities of less than one plant per beet did not reduce beet yields significantly. Rough pigweed alone or combined with green foxtail reduced the beet root yields significantly at all densities in this study. Root yields were reduced 80 percent by two pigweeds and two foxtails per sugar beet. Beet top weights were consistently higher than those of the roots and were reduced approximately in proportion to those of the roots by the various weed densities. The diameter and length of the sugar beets were significantly reduced by competition, the diameter being more affected than the length. The percent sucrose of sugar beets was not affected by weed competition.