Chemical control of parthenium weed (Parthenium hysterophorus L.) in two contrasting cultivars of rice under direct-seeded conditions.
Parthenium weed is an emerging problem in direct-seeded rice due to the suitable microclimatic conditions for its establishment in this system. This two-years field study evaluated the potential of pendimethalin (pre-emergence) and bispyribac-sodium plus bensulfuron-methyl (post-emergence) herbicides to control parthenium weed when applied alone or in combination in two rice cultivars, Basmati-2000 (long duration and tall stature) and Shaheen Basmati (short duration and short stature) under direct-seeded conditions. The cultivar Basmati-2000 had a lower parthenium weed density (27 and 14%) and dry biomass (27 and 25%) but had a greater plant height (8 and 13%), produced more kernels per panicle (8 and 12%) and had a greater grain yield (7 and 9%) when compared to Shaheen Basmati in 2016 and 2017, respectively. The application of pendimethalin followed by bispyribac-sodium plus bensulfuron-methyl provided the highest reductions of 90 and 88% in parthenium weed biomass as compared to the weedy treatment in 2016 and 2017, respectively. In this treatment, rice plants were taller (8 and 10%), having greater panicle lengths (17 and 16%), branches per panicle (11 and 21%), kernels per panicle (9 and 6%), 1000-kernel weight (7 and 9%) and grain yield (33 and 37%) as compared to the weedy treatment in 2016 and 2017, respectively. The highest grain yield and net benefits were recorded in the weed-free treatment. In both years, the sole application of pendimethalin or bispyribac-sodium plus bensulfuron-methyl reduced parthenium weed biomass by 66-69% and 80-82%, respectively as compared to the weedy treatment. Overall, the herbicide treatments followed this order in terms of weed control efficiency, grain yield and economic benefits: pendimethalin followed by bispyribac-sodium plus bensulfuron-methyl > bispyribac-sodium plus bensulfuron-methyl > pendimethalin. In conclusion, rice cultivar Basmati-2000 was more suppressive to parthenium weed due to its tall stature. It also produced higher yields and economic returns than the cultivar Shaheen Basmati. The sequential application of pendimethalin and bispyribac-sodium plus bensulfuron-methyl provided an excellent way to control (ca. 90%) parthenium weed and enhanced the productivity and profitability of both rice cultivars under direct-seeded conditions.