Efficacy of pre-emergence herbicides in controlling Rhynchosia capitata, an emerging summer weed in Pakistan

The weed Rhynchosia capitata is an emerging threat to summer crops in Asia. Among the different management options, chemical control is the most attractive approach due to its higher efficiency. This study evaluated the efficacy of pre-emergence herbicides for the control of R. capitata in mungbean fields in Pakistan. Different pre-emergence herbicides (pendimethalin + prometryn at 525 g, 725 g and 875 g a.i. ha-1; s-metolachlor at 1440 g a.i. ha-1; and pendimethalin at 825 g a.i. ha-1) were evaluated in a 2-yr study program. All the herbicide treatments significantly reduced R. capitata dry weight, macro (NPK) and micronutrient (Cu, Mg, Na, Ca, Fe, Mn and Zn) contents and their subsequent uptake. These significant differences in concentration and uptake of macro and micronutrients by R. capitata were mainly due to its rapid growth rate and more dry matter accumulation during the short available growth period. Among all the treatments, application of pendimethalin + prometryn at 875 g a.i. ha-1 resulted in the most effective control of R. capitata as the highest suppression of the dry biomass (74% and 78% during 2011 and 2012, respectively) was recorded in it. Maximum grain yield of mungbean was also recorded with pendimethalin + prometryn at 875 g a.i. ha-1 and the lowest mungbean yield was recorded in weedy check due to high stress imposed by uncontrolled weeds. The maximum benefit-cost ratio (2.40) was observed in pendimethalin + prometryn at 875 g a.i. ha-1 treatment. This treatment might be a profitable approach for achieving maximum yield of mungbean in areas having high weed infestation.