The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was the main early-season pest of cotton found in large field plot studies conducted from 1981-1984 in Sunflower County, Mississippi. This pest alone, or in combination with lesser numbers of the cotton fleahopper, Pseudatomoscelis seriatus (Reuter), caused significant yield reduction of seed cotton in untreated checks as compared to cotton treated in early-season with various insecticides. The highest plant bug populations were found during 1984, and in this year they reduced the rate of squaring and delayed peak squaring by 1 to 2 weeks in check plots, or plots treated with chlordimeform, as compared to other insecticide treatments in which better plant bug control was achieved. This resulted in a delay in crop maturity of 1 to 2 weeks in the check and chlordimeform treatments. Data collected from 64 cotton fields in Panola County, Mississippi, in 1978-1980 is also presented that shows a delay in crop maturity caused by plant bugs on a county-wide basis in 1979. These results demonstrate that the tarnished plant bug can be a key early-season pest of cotton in the mid-south when uncontrolled populations delay maturity and reduce total yield.