Productivity of wheat (Triticum aestivum) as affected by continuous use of new low dose herbicides for management of littleseed canarygrass (Phalaris minor)

A field experiment was conducted at villages Uchana and Sagga near Karnal, Haryana during rabi of 1998-99 through 2006-07 to study the effect of continuous and rotational use of fenoxaprop, sulfosulfuron and clodinafop on control of Phalar is minor and productivity of wheat. Application of all the 3 herbicides resulted in 35-50% in- crease in wheat yield over weedy plots during first year of application. With continued application of these herbi- cides, the increase in yield remained 23-27% in sulfosulfuron- sprayed plots, 12-23% in fenoxaprop-sprayed plots and 17-35% in clodinafop- sprayed plots in 2005-06 and 2006-07. A similar decline was observed in plots that re- ceived rotational treatment of herbicides. Herbicide sprays resulted in a decline in density of P. minor till 2003-04 after which it increased till 2006-07. In 2006-07 the density of P. minor in some of the herbicide sprayed plots was equivalent to that in the weedy plots. Bioassay test showed increased insensitivity of P. minor to the herbicides. Mortality declined from 85-100% in 2001-02 to 10 % with fenoxaprop and 30-40% with sulfosulfuron in 2006-07. With clodinafop, the decline was relatively lesser. It was upto75% only. GR values of surviving populations 50 showed 10-fold increase than the initial value in sulfosulfuron, 8-fold increase in fenoxaprop and 3-4-fold increase in clodinafop indicating the evolution of cross resistance to these herbicides in this weed.