Boll rot of cotton is incited by a number of fungi and bacteria. Mepiquat-chloride plant regulator (Pix) was effective for controlling boll rot in annual experiments conducted at the University of Tennessee Milan Experiment Station at Milan during 1975-90. Pix treatments to reduce plant size were more effective and more consistent for boll rot control than bottom defoliation and fungicide applications. Excellent yield increases have been obtained in years in which boll rot was a serious problem. Increases up to 276 lb./A. of lint were obtained in 1977, with maximum increases of 160, 246, and 210 lb. in 1979, 1987, and 1988, respectively. Optimum time for application was determined to be early bloom. Pix applications have given control under varying levels of nitrogen fertilization. Growth regulator treatment has been effective under no-till and conventional-tillage situations. Incidence and severity of boll rot have been slightly lower under no-tillage than under conventional tillage. The 0.5-pt./A. rate of Pix has given boll rot control equal to the 1-pt./A. rate. Regrowth after Pix application at a reduced rate has been minimal. Plant coverage has not been a problem; one spray nozzle over the row with a high clearance sprayer has been as effective as three. Split applications have not improved performance over single applications when the total rate used was the same.