Weeds are major obstacles in the successful cultivation of cotton. Many weeds have fast growth; hence they offer severe competition with crops especially in the initial stage. Manual weeding is time-consuming, expensive and tedious. A judicious combination of chemical and cultural methods of weed control seems necessary for effective control of weeds and for the best possible utilization of costly inputs which would ultimately result in higher yields. Therefore, a field experiment was planned and conducted at Agronomy Instructional Farm, Chimanbhai Patel College of Agriculture, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar, Gujarat (India) during kharif 2022 to study the “Effect of weed control treatments on weeds and physiology of Bt cotton grown under North Gujarat agroclimatic conditions of India” on loamy sand soil. The experiment was conducted in a randomized block design with three replications and ten treatments. The Bt cotton variety GTHH 49 was sown manually at a row-to-row distance of 120 cm and 45 cm between plant to plant. Different weed control treatments significantly affected the dry weight of total weeds across the crop growth stages. After weed free plot, the minimum dry weight of total weeds at 25 and 50 DAS was observed under pendimethalin 1000 g/ha as PE + pyrithiobac sodium + quizalofop ethyl 100 (60 + 40) g/ha as PoE at 25 DAS (T 5 ). After weed free plot, the dry weight of total weeds at 75 DAS was found minimum under pyrithiobac sodium + quizalofop ethyl 100 (60 + 40) g/ha as PoE at 25 DAS + IC fb HW at 50 DAS (T 8 ), which had significantly reduced the dry weight of total weeds compared to all other treatments except weed free plot. The maximum dry weight of total weeds at 25, 50, and 75 DAS was observed under a weedy check plot and was significantly higher than all other weed control treatments. Physiological parameters of the crop viz., leaf area index, leaf area duration, chlorophyll content index, and PS Ⅱ quantum were reported maximum under weed-free plot followed by pyrithiobac sodium + quizalofop ethyl 100 (60 + 40) g/haas PoE at 25 DAS + IC fb HW at 50 DAS. The seed cotton yield was reported significantly higher under weed free plot over all other weed control treatments except T 8 which was adjudged at par with weed- free plot. Based on the results of the experiment, it is concluded that T 8 controlled weeds effectively in Bt cotton and gave higher seed cotton yield and net return under North Gujarat conditions.
Parmar et al. (Mon,) studied this question.