South Asia produces slightly above 225 million tons of rice (30.7% of global
production) on 60 million hectares (37.6% of the global area). India and Bangladesh
are the major rice-growing countries. India contributes around a quarter of global
production from 43 million hectares (the largest rice cultivating area). In South Asia,
manually transplanting rice seedlings into flooded soil (TPR) is the common method
of rice establishment. But direct-seeded rice (DSR) is gaining importance due to
shortage and increased cost of resources. In Sri Lanka 93% of rice is cultivated as
wet-seeded rice. However, the weeds are major constraints in DSR causing higher
(14 to 100%) than in TPR (7 to 80%). Major rice weeds in South Asia include:
Echinochloa crus-galli (L.) P. Beauv., Echinochloa colona (L.) Link., Cyperus
rotundus L., Cyperus iria Linn., Cyperus difformis L., red rice (Oryza sativa L.),
Leptochloa chinensis (L.) Nees, Ischaemum rugosum Salisb., Paspalum distichum
L., Dactyloctenium aegyptium (L.) Willd., Cynodon dactylon (L.) Pers., Echinochloa
crus-galli (L.) P. Beauv., Eleusine indica (L.) Pers., and Fimbristylis miliacea (L.)
Vahl. Weeds flora was reported to vary with location, method of rice establishment,
cultural practices used and associated environment. The small-holders’ traditional
weed control method is hand weeding by hand-held hoe and hand pulling. Hand
weeding is still a major method of weed control. However, the herbicide use is
increasing due to non-availability and increased cost of labour in several of the
South Asian countries. Mechanical weeders are being used by farmers as they
reduce labor use and cost of weeding (72 to 74%). Tillage, mulching, crop rotation,
allelopathic competitive crop cultivars, intercropping, balanced nutrient and water
management and preventive measures have proven to be effective as a component
of integrated weed management in rice of South Asian countries. Herbicide resistance
among weeds in rice was not reported in India, Bangladesh, Nepal and Pakistan.
Herbicide resistant biotypes of E. crus-galli, I. rugosum and C. iria were reported
in Sri Lanka. In South Asia, herbicide tolerant rice is yet to be made available to
farming community. Weed management research must be focused on identifying
location specific effective, environment friendly, economically viable integrated
weed management strategies
