MSc

Leptochloa chinensis (L.) Nees. (Chinese sprangletop or Red sprangletop) is one of the most important invasive weeds in direct seeded rice fields. It is a C4 grass species, native to tropical Asia. Although an annual species, it can be perennial under suitable conditions. It is a slender tufted grass growing to a height of 1.2m with smooth linear leaves and terminal loose panicles. In a survey of weeds in rice agroecosystems of Kerala, Chinese sprangletop was first identified as a weed predominant in the alkaline soils of Chittoor taluk. Though this weed was listed as an indicator plant for alkaline conditions (Vidya et al., 2004), it is now seen spreading rapidly in acidic soils also. In Kerala, under the National Invasive Weed Surveillance Programme (2008-11), this weed was reported in rice fields of Palakkad, Kole areas of Thrissur and in Kuttanad region too. This weed has the ability of high seed production and can grow in both flooded and upland conditions. It is reported that the continuous use of bispyribac sodium, a herbicide used for the control of broad spectrum of weeds, has resulted in a shift to the dominance by Chinese sprangletop in wet land rice fields.
With this background, the experiment ‘Herbicidal management of Chinese sprangletop [Leptochloa chinensis(L.) Nees.] in direct seeded rice’ was conducted in a farmer’s field in the kole lands at Pullu in Thrissur district during the period November 2012 - March 2013. Randomized block design was adopted with three replication and twelve treatments and with a plot size of 20 m2. The variety used was Jyothi (PTB 39) which is of 115 days duration. The treatments included application of both pre emergence and post emergence herbicides. The pre emergence herbicides selected were oxyfluorfen sprayed at 3 days after sowing (DAS) and butachlor and pretilachlor both sprayed at 6 DAS. Pyrazosulfuron-ethyl, an early post emergence herbicide, was sprayed at 8 DAS. The herbicides cyhalofop butyl, fenoxaprop-p-ethyl, metamifop, penoxsulam, bispyribac sodium and azimsulfuron, are post emergence in action and were sprayed at 20 DAS. Hand weeded (handweeding at 20 and 40 DAS) and unweeded controls were also included for comparison with the herbicide treatments.



Observations on the weed spectrum, species wise weed count, weed dry matter production, and nutrient uptake by weeds as well as on the rice crop, with special reference to Leptochloa chinensis were taken at 30 DAS, 60 DAS and at harvest using a quadrat of 0.5m x 0.5m size. Major weed species found in experimental plot were grasses which comprised of Leptochloa chinensis, Echinochloa colona, and Echinochloa crusgalli. Ludwigia perennis, Lindernia crustacea, and Alternanthera sp. were the broad leaved weeds and Fimbristylis miliacea, Cyperus iria and Cyperus difformis were the sedges present. Visual phytotoxicity scoring of both weeds as well as crop was done at seven and fifteen days after spraying. As expected, all herbicides showed phytotoxic effect on weeds with scoring ranging from 2 to 4 indicating moderate control to very good control. Fenoxaprop-p-ethyl resulted in the phytotoxic symptoms on weeds in the form of purple blotches on leaves. The dry matter production of Leptochloa chinensis was seen increasing from 30 DAS to harvest in most of the treatments. Comparing the different herbicidal treatments, fenoxaprop-p-ethyl was most effective in controlling grass weeds including Leptochloa at all stages of observation, followed by cyhalofop butyl which was the next best herbicide as evident from the lower weed occurrence and production of dry matter as well as higher weed control efficiency. The highest grain yield of 6.46 t/ha was recorded in hand weeded control plot followed by fenoxaprop-p-ethyl (5.88 t/ha), and lowest yield was obtained in unweeded control. Highest B:C ratio of 2.1 was recorded by fenoxaprop-p-ethyl. Grain yields produced on application of all the other herbicides were significantly lower than that in handweeding and fenoxaprop-p-ethyl.
Thus the study brings out the superiority of fenoxaprop-p-ethyl in controlling Leptochloa chinensis. Cyhalofop butyl was also seen to be an effective herbicide for this purpose. However, these herbicides were ineffective in controlling broad leaf weeds and sedges. The treatment bispyribac sodium controlled broad leaf weeds like Ludwigia parviflora and sedges like Cyperus spp. and Fimbristylis miliacea. Although bispyribac sodium was ineffective in controlling Leptochloa, it still produced reasonable grain and straw yields. The
results indicate that for the specific control of Leptochloa chinensis, the best herbicide would be fenoxaprop-p-ethyl 60 g a.i./ha or cyhalofop butyl 80 g a.i./ha, both applied at 20 DAS and in areas where Leptochloa is not a severe problem, bispyribac sodium 30 g a.i./ha at 20 DAS can be recommended for controlling grasses, sedges and broad leaf weeds.