Abstract:
Weeds, affecting both quality and quantity of the production are recognized as the major biotic constraint
in rice in Sri Lanka. The production losses incurred due to weeds have been estimated as 20%-40%
(valued 200-400 million USD/annum) that depend on the climate, crop management and efficacy of
adapted weed management practice. Thus, weed management would contribute a lot in closing the yield
gap of rice cultivation. This study was conducted to demonstrate farmers how yield is maximized through
proper weed management in Kalinga-ela and Ambanganga of Polonnaruwa District in 2015 Yala Season.
Herbicides namely Pretilachlor 300g/l+ Pyribenzoxim 20g/l EC, Bispyribac sodium 40g/l + Metamifop
100g/l SE, Pretilachlor 300g/l EC, Pretilachlor 170g/l + Propanil 330g/l EC were evaluated against no-herbicide control in demonstration plots. Parachute method without herbicide, Row seeding with weeders
and Farmers' Practice (Random Seed Broadcasting with herbicides) were evaluated in another set of
demonstration experiments. When obtaining samples in order to have replicates, 03 samples were taken
randomly in each plot so that data were analyzed as a RCBD. Initial weed flora was observed and recorded
in the experimental site. Weed counts at 06 weeks after treatment, weed dry weight at 06 weeks after
treatment and final grain yield were recorded. Weed control efficacy or weed control efficiency was
calculated for each treatment using the standard equation. Pretilachlor 300g/l+ Pyribenzoxim 20g/l EC,
Bispyribac sodium 40g/l + Metamifop 100g/l SE, Pretilachlor 300g/l EC, Pretilachlor 170g/l + Propanil
330g/l EC showed a significantly lower weed dry weight and a significantly higher grain yield than the
control. Parachute method followed by no-herbicide performed well in equally with Random Seed
Broadcasting Method followed by herbicide. It is clear that Parachute method is an alternative for
herbicides.
