Abstract:
A field experiment was conducted usingl0 rice varieties {At306, AERON9-3, 89352, AERON10-26, At10-
1240, 1R09N247, Zhonghua, Bw1L-3403, AtL0-1327 and Suwandal_) in Rice Research and Development
institute, Batalagoda during Yala 20L5 and Maha 201-5/2016 seasons in order to evaluate weed
competitiveness in rice selected varieties. Plot size was 18 m2. Wet- Direct seeding with the rate of
l00kg/ha was practiced as the crop establishment method which is the most adopted method by Srl
Lankan paddy farmers. Weed counts at 06 weeks after establishment, weed dry weights at 06 weeks after
establishment, Plant height at weekly intervals, Leaf length at weekly intervals, percentage canopy closure
using beaded string method at weekly interval till varieties reach 100%o ground cover and final grain yield
were rneasured. Yield reduction percentage for each rice variety was calculated by standard formulae.
Weed competitiveness was calculated according to formulae of S. S. Harding and A. B. falloh, 201-3. Data
were analyzed using SAS software employing GLM procedure. Bw11-3403 and At10-1327 were very
highly weed competitive [VHC]. AER0N9-3, AERONl0-26, At10-1240 and Zhonghua were highly weed
competitive [HC). Bg352 were competitive [C). IR09N247 and Suwandal were moderately weed
::rpetitive [MCJ. These lines showed a faster conopy closure over the time compared to other tested
lines which is a favourable character for weed suppression. This weed competitiveness character can be
used in future breeding programs. Weed competitive rice cultivars can effectively incorporated into
intergrated weed management package and it will enable minimizing chemical herbicide usage.
