Herbicidal weed control in boro rice

An experiment was carried out during December 2008 to June 2009
at the Agronomy Farm of Bangladesh Agricultural University,
Mymensingh to study the effectiveness and economic importance of
herbicides, in boro rice varieties: Surjamoni and BRRI dhan29. Ten
weed control treatments were weedy check; Aimchlor 5G @ 25 kg
ha-1; 20 kg ha-1; 30 kg ha-1; Topstar 400SC @ 190 ml ha-1; 152 ml
ha-1; 228 ml ha-1; Superheat 500EC @ 1.0 l ha-1; 0.80 l ha-1 and 1.20
l ha-1. Among the herbicides Superheat 500EC @ 1.20 l ha-1 was the
most efficient with the lowest weed population, weed dry weight and
highest weed control efficiency with the variety BRRI dhan29. Yield
and yield contributing characters such as plant height, grains/panicle,
1000-grain weight, grain and straw yields were significantly
influenced by the interaction between variety and weed control
treatments. Among the herbicides, Topstar 400SC @ 152 ml ha-1
produced the highest grain yield (5.0 t ha-1) which was 57.73%
higher than control (3.17 t ha-1) in case of tall variety, Surjamoni.
Maximum gross margin with Superheat 500EC @ 1.20 l ha-1
suggested that this herbicidal treatment can be used as an
alternative when labor is a limiting factor in boro season rice
cultivation. Visual observation indicated that all three herbicides were
not so toxic to rice plants. There were 3 different weed species
infested the field among which Echinochloa crusgalli followed by
Paspalum distichum was the most dominated weeds in terms of
weed density and importance value.