Changing scenario of weed flora in agroecosystems of Punjab.
Changes in wheat genotypes, from tall, low yielding genotypes to short, high yielding genotypes were shown to affect weeds, such that the DW of Phalaris minor, Melilotus indica and Chenopodium album were increased from 1.4, 3.7 and 6.6 g to 3.5, 6.7 and 11.0 g, resp. Different sowing dates (Oct., Nov. and Dec.) were shown to affect wheat yields (2050, 3830 and 3070 kg/ha, resp.) and weed DW (450, 960 and 450 kg/ha, resp., for P. minor; 510, 260 and 280 kg, resp., for M. indica and 1240, 280 and 440 kg, resp., for C. album). Irrigation also affected crop yields and weed DW; 1, 3 and 6 irrigations resulted in wheat yields of 2910, 3970 and 4190 kg/ha, resp., and C. album DW of 1690, 1920 and 1070 kg, resp. Crop plant density and its effect on weed DW is discussed. The use of tillage and crop rotation for weed control is mentioned. Herbicide use for weed control, and problems of tolerant weed species (notably Ischaemum rugosum, Caesulia sp., Sphenoclea sp. and Ammannia sp. to butachlor, and Medicago denticulata, Melilotus indica, Silene conoidea, Lepidium sativum [cress] and Lathyrus sp. to isoproturon) are discussed.