Vegetative diversification with weeds can enhance natural enemy populations and suppress pest-related damage in various crops. Weedy and weed-free cotton (Gossypium hirsutum L.) plots were used to study the effects of weediness on selected herbivorous arthropod groups, including the boll weevil (Anthonomus grandis grandis Boheman), and natural enemies, boll weevil-induced injury to cotton squares, and cotton plant growth and yield in the Lower Rio Grande Valley of Texas, during 2000 and 2001. The presence of weeds was associated with greater populations of 9 of the 11 prey arthropod groups, and 9 of the 13 natural enemy arthropod groups counted in this study. These trends were mostly evident late in the season when weed biomass was greatest. Weed-free cotton harbored more cotton aphids (Aphis gossypii Glover), early in the season and silverleaf whiteflies (Bemisia argentifolii Bellows and Perring) later in the season than weedy cotton on some of the sampling dates. Diversity (Shannon’s index) within the selected arthropod groups counted in this study was significantly greater in dvac samples from the weed foliage than from weed-free cotton plants during both years, and diversity on weedy cotton plants was greater than on weed-free cotton plants during 2000. Boll weevil oviposition injury to squares was unaffected by weeds, but the higher weed-associated predator populations mainly occurred after most squares had become less vulnerable bolls. Weed competition resulted in lower lint yields of 89% and 32% in the 2 yr.