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Three types of weeds are found in rice ﬁelds in Andhra Pradesh i) Grasses : Monocots, two ranked leaves
ii) Sedges : Similar to grasses but have 3 ranked and triangular solid stems. They frequently have modiﬁed rhizomes adopted for storage and for propagation. Sedges belong to the family cyperaceae, a large family of monocotyledonous plants distinguished chieﬂy by having active solid stems and 3 ranked stem leaves.
|Echinochloa colonum,Echinochloa crussgelli, cynodon sps panicum sps
||Cyperus rotundus, Cyperus iria, Fimbristylis miliaceae
||Eclipta alba, Commelina bengalensis, Ammonia baccifera
| Control of weeds
• Flooded condition of rice ﬁeld reduces weed intensity.
• Transplanting of rice seedlings in weed free ﬁelds.
• Hand weeding is done whenever necessary with an interval of 20-25 days to remove the perennnial and large weeds.
• Mechanical weeding is done with the help of cono weeder or roto weeder.This is useful in the removal of small weeds like 2-3 leaved weeds.
Chemical control of weeds
• Pyrazosulfuron ethyl 10 % -250g / ha, mixed with 30 kg of sand or 500 lit of water and applied 3 - 5 days after transplanting. Or
• Pretilachlor 50 EC - 1.5 lit / ha, mixed with 30 kg of sand or 500 lit of water and applied 3 - 5 days after transplanting.Or
• Butachlor 5 % - 30 kg / ha, mixed with 30 kg of sand or 500 lit of water and applied 3 - 5 days after transplanting.
• Bensulfuron methyl + Pretilachlor (6.69) - 10 Kg / ha, mixed with 30 kg of sand or 500 lit of water and applied 3 - 5 days after transplanting.
Biological Weed Control
• Natural or biological weed control agents are those of biological origin, which suppress or kill the weeds without signiﬁcantly affecting the desirable plants. They include insects, animals, ﬁsh (like Chinese carp), snails, birds (like duck), microbes (fungi, bacteria, viruses, nematodes, etc.), their toxic products, and plants (parasite plants, competing plants) or their products.
• Animals, like pigs feed on the tubers of purple nutsedge (C. rotundus) in the off-season. In control of Ludwigia parviﬂora in rice ﬁelds, steel blue beetle (Haltica cyaamea) and larvae of Bactra verutana were found to bore into shoots of Cyperus rotundus.
• Plant pathogen, Colletotrichum gloeosporioides sp. Aeschynomene was found effective for control of Aeschynomene virginica and Colletotrichum gloeosporioides sp. Jussiaceae for the control of Ludwigia decurrens.
• Other Pathogens that have been shown potential as biological control agents for controlling weeds in rice, include Drechslera monoceras for the control of Echinochloa crusgalli, Epicoccosorus nematosporus for the control of Echinochloa kuroguwa. Biocontrol of E. kuroguwai has become possible by means of a plant pathogen, Epicoccosorus nematosporus, and of Scirpus planculmis by a pathogen Alternaria sp.