A research trail was conducted to determine the effect of defoliants on defoliation and yield of cotton. Cotton (Gossypium hirsutum L.) cultivar ‘Suraj’ was planted during kharif 2016 and defoliants were sprayed at 60 boll opening percentage (BOP). A degree day above than 100°C was required after defoliants application for completion of defoliation process and opening of boll. The atmospheric minimum and maximum temperatures of and °C, respectively, were found conducive for inducement of defoliation process. | Effectiveness of harvest Aid defoliants and environmental conditions in high density cotton