Interaction of Stage of Application and Herbicides on Some Phalaris minor Populations

Pot studies were carried out at Agronomy Research Farm of CCSHAU, Hisar during the rabi seasons of 2005–06, 2006–07 and 2007–08 using isoproturon resistant, susceptible and pristine populations of Phalaris minor. Ten herbicides (isoproturon, chlorotoluron, sulfosulfuron, clodinafop-propargyl, fenoxaprop-P-ethyl, quizalofop-ethyl, premix of mesosulfuron-methyl+iodosulfuron-methyl-sodium, sulfosulfuron+metsulfuron-methyl, pinoxaden and tank mix of pinoxaden+carfentrazone-ethyl) were applied at two growth stages (4 leaf and tillering) of five P. minor populations [J-35 (Jind), F-42 (Fatehabad), K-15 (Karnal), H-2 (Hisar) from Haryana and B-6 (Bihar)] using three application rates by a knapsack sprayer fitted with flat fan multi nozzle boom delivering 500 l water/ha. The pots were arranged in a CRD design with three replicated earthen pots for each herbicide treatment and populations. Plant height, weed mortality and fresh/dry weight were recorded to evaluate herbicides effect on P. minor populations. When combined data were analyzed, no significant interaction of weed stage, populations and herbicides was observed for per cent mortality and dry weight, whereas highly significant effect of weed stage, populations and herbicides was recorded. There was significant interaction of populations and herbicides for mortality data. Significant interaction for stage, dose and herbicides was recorded when data for each population at two growth stages were subjected to ANOVA, which shows large variations among populations to different herbicides. P. minor populations, J-35 and K-15 had significantly lower mortality and higher dry weight, data averaged over herbicides, compared to B-6 and H-2, whereas F-42 was intermediate in mortality and accumulated higher dry weight compared to B-6 and H-2. Among the herbicides, lowest mortality was recorded with clodinafop and isoproturon followed by fenoxaprop and quizalofop, whereas highest mortality was recorded with pinoxaden tank mixed with carfentrazone and its alone application followed by chlorotoluron and mesosulfuron+iodosulfuron. Sulfosulfuron alone and premix with metsulfuron had lower mortality compared to pinoxaden±carfentrazone and chlorotoluron. Similar results were recorded for dry weight also. Delayed application from 4 leaf to tillering stage lowered the mortality of sulfosulfuron±metsulfuron, mesosulfuron+iodosulfuron, isoproturon and chlorotoluron. The GR50 (growth reduction by 50%) of herbicides increased with stage of herbicide application; increase was more in isoproturon and clodinafop compared to other herbicides. Populations, K-15 and J-35 had resistance factor (Rf) of 10.85 and 4.91 for isoproturon and 1.70 and 1.25 for clodinafop, respectively, when applied at tillering stage compared to H-2 population. Some variations were also observed in GR50 with other herbicides, but not reflected in dry weight. The study indicated ensuing problems with clodinafop, fenoxaprop and even sulfosulfuron, but there was no loss of efficacy with pinoxaden±carfentrazone or chlorotoluron.