Effect Of Sequential Application Of Pre And Post-Emergence Herbicides On Dynamics Of Weeds Associated With DSR System Andrice-Growth And Sustained Yield

Abstract

The sustained rice yield plays an important role in the country’s GDP. The diverse weed flora is a potential biotic threat to the sustained yield in the DSR system. The crop faces severe competition the resources from its beginning (germination of crop seedlings) to the panicle initiation with the diverse weeds flora as it grows quickly in moist conditions, resulting in severe yield losses up to 65 per cent. Thus, an effective and economical weed control strategy in DSR is often required to overcome the losses. In such situations, sequential application of herbicides may provide broad-spectrum weed control in DSR. A field experiment was conducted on silty loam soils to assess the herbicidal effects on weed dynamics and growth & yield productivity of direct-seeded rainy (Kharif) rice at Agronomy Research Farm of Narendra Deva University of Agriculture and Technology, Kumarganj, Ayodhya (U.P.) during the years, 2016 and 2017. The field trial was carried out in Randomized complete block design (RCBD) with three replications and twelve treatments. The treatments consisted of nine pre & post-emergent herbicide combinations along with three distinct controls, i.e. a) Hand weeding (at 20 & 40 DAS), b) Weed Free (weeding at every 15 days interval from seedling to the PI stage), and c) Weedy Check. The results of the field study revealed that the weed-free plots recorded the highest weed control efficiency, and they registered the least weeds density and dry weight of weeds associated with direct seeded rice fields. However, the application of herbicides, namely, pendimethalin (1000 g a.i. ha-1) as pre-emergent and Bispyribac-Na (1000 g a.i. ha-1) as post-emergent coupled with a hand weeding at 40 DAS provided the statistically comparable results to weed-free and is effectively controlled the diverse weed flora by 81.9-84.5 per cent in DSR system. And both the treatments gave significantly better growth (plant height, number of tillers, dry matter, LAI) and yields (grain and straw) of rice as compared to the weedy-check. Among the diverse weeds associated with the DSR fields, sedges were dominant as compared to broad leaves and grasses. The study also recorded the rice-grain yield reduction by 40.9 per cent due to the presence of diverse weed flora in weedy check plot as to weed-free plot.