Effect of sulphonyl urea herbicides on weed control in wheat (Triticum aestivum).
The efficiency of weed control by sulfonylurea herbicides compared to hand-weeding 35 days after sowing in wheat cv. HD2285 was studied in field trials on sandy loam at New Delhi during 1990-91 and 1991-92. The following herbicide treatments were applied with the surfactant Teepol: 2, 4 or 8 g/ha metsulfuron-methyl; 5.0, 7.5 or 10.0 g/ha terbutron [terbutryn]-methyl; 5 + 500 g/ha metsulfuron-methyl + isoproturon; 2 + 500 g/ha terbutron-methyl + isoproturon; 600 g/ha 2,4-D; 1000 g/ha isoproturon; and 1000 g/ha isoproturon + 2,4-D (suspension without Teepol). The 4 g/ha metsulfuron-methyl and 5 g/ha terbutron-methyl treatments were also applied without Teepol. Metsulfuron-methyl killed all creeping thistle (Cirsium arvense) plants, whereas terbutron-methyl was ineffective against this weed. Both of these herbicides inhibited the growth of the grass weeds present (Avena fatua and Phalaris minor) for a month and gave good control of broadleaved weeds (mainly Chenopodium album, Melilotus indica and Anagallis arvensis). Their combination with isoproturon was not advantageous. Isoproturon was most effective against the grass weeds and gave satisfactory control of broadleaved weeds. 2,4-D gave good control of broadleaved weeds and arrested the growth of Cirsium arvense, but encouraged the growth of the grass weeds. The herbicides were ineffective against dear's foot (Convolvulus arvensis). Hand-weeding was better than herbicide treatment for weed control. However, similar significant increases in grain yield were observed for herbicide and manual control compared to the control (no weed control) crop. Isoproturon suspension was inferior to its wettable powder formulation. Addition of surfactants increased weed killing activity of herbicides and wheat grain yield.