Efficacy of Post‐Emergence Herbicides for Weed Control in Spring–Summer Blackgram ( Vigna mungo L. Hepper) and Their Residual Effects on Direct Seeded Rice ( Oryza sativa L.)

There is a need for effective post‐emergence (POST) herbicides to manage diverse weeds, particularly monocot weeds, in blackgram ( Vigna mungo L. Hepper) for its successful integration in cereal‐based systems of the Indo‐Gangetic Plains. However, the poor efficacy of the currently recommended POST imazethapyr against Echinochloa colona , a predominant monocot weed in these systems, limits wider adoption of blackgram. This study aimed to identify effective POST herbicides for use in blackgram, and to assess their residual effects on soil microbial populations and succeeding direct‐seeded rice ( Oryza sativa L.) productivity. Accordingly, the field experiment was conducted for 2 years (2020 and 2021) in a randomized block design with four replications, comprising seven treatments: weedy check, imazethapyr 75 g a.i. ha −1 , clodinafop‐propargyl + acifluorfen sodium (ready‐mix) 187.5 g a.i. ha −1 , propaquizafop + imazethapyr (ready‐mix) 125 g a.i. ha −1 , quizalofop‐p‐ethyl + imazethapyr (tank mix) 50 + 75 g a.i. ha −1 , imazamox + imazethapyr (ready‐mix) 60 g a.i. ha −1 , and hand weeding. A total of 11 weed species were recorded, with grasses, including E. colona, constituting nearly 80% of the total weed population, while the only sedge species, Cyperus rotundus , accounted for 7.8%, indicating predominance of monocot weeds. Propaquizafop + imazethapyr and quizalofop‐p‐ethyl + imazethapyr significantly reduced monocot weed density by 40.6%–44.1% and 27.5%–32.5% compared with the recommended imazethapyr at 25 and 65 days after sowing. Compared to the weedy check, propaquizafop + imazethapyr and quizalofop‐p‐ethyl + imazethapyr effectively suppressed total weed density (i.e., weed control efficiency, 62.8%–64.7%) and dry matter (i.e., weed control index, 72.1%–74.4%). They also produced 30.9%–37.1% higher yield over currently recommended sole imazethapyr. None of the tested herbicides exerted any detrimental effects on soil microbes or yield of the succeeding rice crop. Therefore, propaquizafop + imazethapyr or quizalofop‐p‐ethyl + imazethapyr as POST herbicide can effectively control weeds, especially monocots and may be recommended for spring–summer blackgram cultivation in rice‐based systems.