Efficacy of herbicides in controlling Parthenium hysterophorus L. in spring maize (Zea mays L.)

Parthenium hysterophorus L. is a noxious annual weed rapidly spreading in cropped areas of the irrigated Punjab and other parts of Pakistan. It has become a major threat to grazing lands and crops in Punjab province. The main objective of this study was to explore the efficacy of different herbicides with various concentrations viz. pendimethalin, S-metolachlor + atrazine, bromoxynil + 2-methyl-4-chloorphenoxyacetic acid, and atrazine at their recommended (407, 711, 445 and 469 g a.i./ha, respectively), 50% lower and 50% higher doses against Parthenium hysterophorus L. Weeds were allowed to grow in a field for three years (2010-2013) where this spring maize experiment was conducted during the years 2013 and 2014. All herbicide treatments at their recommended and higher doses significantly reduced Parthenium dry weight. Minimum density (2.3 and 2.0/m) and dry biomass (39.74 and 43.47 g/m) of parthenium weed was observed with S-metolachlor + atrazine at 711.36 g/ha treatment during 2013 and 2014, respectively. A herbicide efficiency index of 88% was observed with S-metolachlor + atrazine at 711.36 g a.i./ ha in 2013 and 2014, respectively. Among the herbicides, atrazine, bromoxynil and metolachlor gave significantly the lowest dry weight of Parthenium. Maximum 1000-grain weight (259 and 260.67 g), grain yield (4.86 and 4.87 t/ha), stalk yield (5.60 and 5.42 t/ha) and biological yield (14.80 and 13.80 t/ha) were recorded during both years of experiments when S-metolachlor + atrazine at 711.36 g/ha was applied. These results suggested that over- and underdose of S-metolachlor + atrazine significantly lower the maize growth and yield attributes by allowing more Parthenium density at a lower dose, while causing a toxic effect on the maize plants at a higher dose of herbicides. So, the application of S-metolachlor + atrazine (post-emergence) at the recommended rate minimised the weed-crop competition at all the critical crop growth stages, and ultimately yielded the better crop harvest during both years of study.