Field experiments were conducted during 1987 and 1988 at Jackson and Grand Junction, Tennessee to determine if interference of common cocklebur (Xanthium strumarium L.), johnsongrass (Sorghum halepense L.), palmer amaranth (Amaranthus palmeri) at 1 plant/l m row, or morningglory (Ipomoea hederacea spp.) at 1 plant/0.5 m row differed between no-tillage and conventional tillage. At the 900 to 1200 kg/ha lint yield level, losses from common cocklebur, Palmer amaranth, morningglory and johnsongrass were 35, 39, 33, and 32%, respectively, in conventional cotton compared to 23, 28, 29, and 12% for no-tillage. Densities of morningglories twice that of the other weeds were required to give similar yield loss. With all four weeds, yield losses were higher with conventional tillage, yet there were no differences between tillage systems in the absence of weeds. Palmer amaranth and johnsongrass caused yield loss in adjacent rows, indicating an area of influence greater than common cocklebur or morningglory. This may be a result of the taller growth habit of these species compared to common cocklebur and morningglory indicating that interference studies with Palmer amaranth and johnsongrass should include the effects of these species on adjacent rows. There was a trend for lower grade in the presence of weeds, especially with johnsongrass and morningglory. Tillage did not influence grade.