Field experiments were conducted during summer 2016 and winter 2016-17 at Agricultural College and Research Institute, Madurai to study the allelopathic effect of different intercrops and tree leaf extracts in managing weeds and increasing productivity of cotton. The cotton + sorghum intercropping system registered lower weed density at 20, 40 and at 60 days after seeding (DAS) during both the seasons. Among the weed management practices, lower weed density was recorded with pre-emergence application of pendimethalin at 1.0 kg/ha at 20 DAS and with hand weeding twice at 20 and 40 DAS at 40 and 60 DAS during studied periods. The highest cotton equivalent yield (389, 419       kg/ha), land equivalent ratio (1.52, 1.54), monetary equivalent ratio (1.18, 1.17) and system productivity (2.13, 2.39 t/ha) were recorded in cotton + sunflower intercropping system with hand weeding twice at 20 and 40 DAS during both the years. Among the combined applications of intercropping system and tree leaf extracts, cotton + sunflower (1:1) + pre-emergence application of Mangifera indica leaf extract at 30% + hand weeding at 40 DAS registered the maximum cotton equivalent yield (349, 374 kg/ha), land equivalent ratio (1.31, 1.34), monetary equivalent ratio (1.0, 1.02) and system productivity (1.81, 2.07 t/ha) during summer 2016 and winter 2016-17, respectively.