Conservation tillage cotton production systems are rarely utilized in South Texas although they have several production advantages over conventional tillage systems. The objective of this study was to evaluate the effect of weed and insect populations on cotton yield and production economics of cotton grown in conventional (CT), reduced tillage (RT), and pre-plant no-tillage (PPNT) systems. A split-plot, randomized complete block experimental design was used on the three tillage systems. Main plots were tillage system and the split plots were rotational schemes within the tillage system. Weed and insect levels, and plant growth and yield parameters were measured throughout the growing season. Lint yield of the PPNT system was not statistically different from CT in the Lower Rio Grande Valley, Weslaco, TX in 1993. However lint yield of RT was significantly reduced from the other two tillage systems. The PPNT system resulted in net returns which were 17% greater ($193.51 -vs- $161.30 per acre) than CT. Acceptable weed control was obtained in all tillage systems; however, a pre-plant burndown herbicide and a post-emergence grass control herbicide were used in RT and PPNT systems which resulted in greater herbicide costs for these systems. Tillage costs were much less in the RT and PPNT systems ($37 and $45/acre lower) than in the CT system. Whitefly populations and boll weevil damage were not different for the three tillage systems, although bollworm/tobacco budworm cotton boll damage was slightly greater in the CT system. Eleven applications of insecticides kept all insect populations and damage in check all season.