The effects of hogpotato interference on cotton and of the crop on the weed were measured under field conditions in four environments. Full-season interference from 105 ± 21 hogpotato plants/m2 reduced cotton plant height by 14 to 44%. Conversely, weed dry weight was reduced 54% through full-season interference from cotton. Lint yield reductions in cotton ranged from 31 to 98% following full-season weed interference. Interference during the first 7 weeks of crop growth reduced lint yield by approximately 40%; however, interference after 7 weeks of weed-free maintenance did not affect lint yield. Interference reduced boll size in 3 of 4 yr, lint percent in 2 of 4, and boll number in the only year it was measured. Cotton fiber length, uniformity index, and micronaire were reduced by full-season interference in 1 of 2 yr; however, fiber strength was not affected in either year. Significant use of soil water by hogpotato occurred at 120 cm and deeper in the soil while cotton used water primarily in the upper 75 cm.