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chemical weed control in direct seeded rice

Two field experiments were conducted at Ngala in the Lake Chad Basin during the 1981 and 1982 wet seasons to investigate chemical weed control in direct-seeded, irrigated rice (Oryza sativa L.). Pre-plant-incorporated, pre- and post-emergence herbicides and their mixtures were tested in replicated, completely randomized block trials. Rice variety IR 28 was drilled each season at 125 kg/ha and fertilized with N (150 kg/ha) and P2O5 (40 kg/ha). In both seasons, the post-emergence herbicides propanil + oxadiazon at 3·0 + 1·0 kg a.i./ha, propanil+fluorodifen at 1·4 + 1·8 kg a.i./ha, propanil + bentazone at 3·6 + 1·5 kg a.i./ha and propanil at 3·6 kg a.i./ha as well as thiobencarb applied pre-emergence at 5·0 kg a.i./ha controlled the weeds effectively and gave similar grain yields to that from hand-weeding twice, and significantly higher grain yield than the unweeded control treatments. Grain yields similar to those from the ‘two hand-weeding control’ were achieved also by use of the herbicide dymrone at 3·0 kg a.i./ha, either soil-incorporated pre-sowing or sprayed before weed emergence. The herbicides gave satisfactory control of the weeds, which were predominantly the broad-leaved weed Luffa echinata Roxb., together with the grasses Sorghum aethiopicum (Hack.) Rupr. ex Stapf., Echinochloa colona (L.) Link, Eleusine indica (L) Gaertn, Digitaria sanguinalis (L.) Scop., Oryza longistaminata (Chev. & Roehr.), and sedges Cyperus rotundus L. and Cyperus esculentus L. The studies indicate that effective weed control by these herbicides and herbicide mixtures are dependable alternatives to hand weeding for direct-seeded, irrigated rice cultivation in the Chad Basin area.

Present address: School of Agriculture, Tafawa-Balewa College, Ahmadu Bello University, PMB 0248, Bauchi, Nigeria.

Across the locations, all weed control treatments provided significantly higher return over variable cost (ROVC) and B:C ratio compared to weedy check. Sequential application of herbicides proved superior to sole application of herbicides either PRE or POST at both the sites. The sequential application of pendimethalin PRE fb bispyribac-sodium + azimsulfuron POST was superior over other herbicide treatments and non-treated weed-free treatment in terms of B:C ratio at both the sites ( Table 7 , Table 8 ). At both sites application of bispyribac-sodium after pendimethalin PRE provided significantly higher ROVC and B:C compared to its application after oxadiargyl PRE. Azimsulfuron as POST application performed well compared to bispyribac-sodium in terms of B:C ratio and ROVC owing to higher infestation of broadleaved weeds at Madhuban. Bispyribac-sodium was inferior to azimsulfuron in controlling broadleaved weeds and resulted in lower yield at this location.

Efficacy of herbicide treatments at 20 DAS and 45 DAS, CSISA research platform, Taraori, Karnal, India (2010).

Azimsulfuron was commercialized in India in 2012. It was a new herbicide for Indian market then and only few studies had been conducted on azimsulfuron. Since the area under DSR sharply increased in Haryana, India, in 2010, it necessitated the testing of new herbicide molecules for herbicide efficacy and crop safety especially for scented rice which has huge export potential and Haryana is the major exporter of scented (basmati) rice.

3.1.3. Yield and yield parameters

At each location, a burndown application of glyphosate (1.0 kg ai ha −1 ) was made on the experimental area in mid-May 2010 and was followed by a light tillage with one pass of disc harrow and one pass of spring loaded tyne cultivator followed by planking before seeding. Fungicide-treated ([email protected] 0.5 g ai kg −1 rice seed) seeds of ‘CSR 30’ cultivar (superfine, scented; basmati cultivar) were planted in the second week of June, 2010, at both the locations. Seeds were drill-seeded at a rate of 20 kg ha −1 with a multi-crop seed-cum-fertilizer planter (Dasmesh ® ) at 2–3 cm soil depth. Light irrigation was provided immediately after seeding. All PRE herbicides except oxadiargyl (sand mix application), were sprayed on the third day of irrigation. Oxadiargyl was mixed with sand (8 kg ha −1 ) and broadcast in standing water (2–3 cm) after irrigation on the day of seeding (general farmer practice). All POST herbicides, except sequential PRE application of oxadiargyl, were applied at three-to four-leaf stage of rice [20–22 days after seeding (DAS)]. The sequential oxadiargyl was applied at the two-to three-leaf stage of rice (15 DAS). The herbicides were applied using a battery operated back-pack knapsack sprayer fitted with a flat-fan nozzle and calibrated to deliver 500 L ha −1 for PRE spray and 375 L ha −1 for POST spray. The area of each plot was 24 m 2 (6 × 4 m). The crop was managed following the standard recommended practices for the region. Fertilizers, 25 kg N, 30 kg P2O5, and 25 kg ZnSO4 ha −1 , were applied as a basal dose. N and ZnSO4 were broadcasted uniformly and P2O5 was applied using a multi-crop seed-cum-fertilizer planter while planting. Remaining amount of N (50 kg ha −1 ) was applied in two splits at 40 and 60 DAS. Two sequential foliar sprays of 1% FeSO4 were applied at 40 and 47 DAS, though only the Madhuban location showed iron deficiency at this stage. After the first irrigation at the time of seeding, the second light irrigation was applied 5 DAS. Subsequent irrigations were provided at a weekly interval except tillering and panicle emergence stage. Irrigations were applied at 3–4 days interval at tillering stage and during panicle emergence.

The density of grasses, broadleaf weeds and sedges was lower with PRE herbicide treatments compared to weedy check. The density of grass weeds was 12–16, 21–31, and 20 plants m −2 following PRE application of pendimethalin, oxadiargyl and butachlor, respectively, compared to 51 plants m −2 in the weedy check at 20 DAS ( Table 6 ). The density of broadleaf weeds was reduced by 66–88% with PRE herbicide treatments compared to weedy check. The reduction in weed biomass was in the range of 50–73% with PRE herbicides compared to weedy check. The reduction in density of grasses, broadleaved weeds, and sedges was similar in all the treatments with sequential POST applications of the herbicides and significantly lower densities were observed compared with single PRE application of oxadiargyl and weedy check treatment. The weed biomass was reduced by 67–86% with the sequential application of pendimethlin PRE fb either azimsulfuron or bispyribac-sodium or both together as tankmix application compared to weed biomass reduction of 62–73% with oxadiargyl PRE fb azimsulfuron or bispyribac-sodium at 45 DAS ( Table 6 ).

Performance of rice (‘CSR 30′) in response to herbicide treatments, CSISA research platform, Madhuban, Karnal, India (2010).

Farmers’ participatory field trials were conducted at Madhuban, and Taraori, the two participatory experimental sites/locations of the Cereal Systems Initiative for South Asia (CSISA), a collaborative project of IRRI and CIMMYT in Karnal district of Haryana, India, during Kharif (wet season) 2010 and 2011. This research aimed to evaluate preemergence (PRE) and postemergence (POST) herbicides for providing feasible and economically viable weed management options to farmers for predominant scented rice varieties. Treatments with pendimethalin PRE fb bispyribac-sodium + azimsulfuron POST had lower weed biomass at 45 days after sowing (DAS). At Madhuban, highest grain yield of scented basmati rice (3.43 t ha −1 ) was recorded with the sequential application of pendimethalin PRE fb bispyribac-sodium + azimsulfuron POST. However, at Taraori, yields were similar with pendimethalin or oxadiargyl PRE fb bispyribac-sodium and/or azimsulfuron POST. Applying oxadiargyl by mixing with sand onto flooded field was less effective than spray applications in non-flooded field. The benefit-cost ratio of rice crop was higher with herbicide treatments at both sites as compared with the non-treated weed-free check except single PRE and POST applications and sequential application of oxadiargyl PRE fb oxadiargyl PRE. In a separate experiment conducted at Nagla and Taraori sites, scented rice cultivars’ (‘CSR 30′ and ‘Pusa 1121′) tolerance to three rates of azimsulfuron (15, 25, and 35 g ai ha −1 ) was evaluated over two years (2010 and 2011). CSR 30 (superfine, scented) was more sensitive to higher rates (35 g ai ha −1 ) of azimsulfuron as compared to Pusa 1121 (fine, scented). Crop injuries were 8 and 28% in case of CSR 30; 5 and 15% in Pusa 1121 when applied with azimsulfuron 25 and 35 g ai ha −1 , respectively. Azimsulfuron applied at 35 g ai ha −1 reduced yield in both cultivars but in CSR 30 yield reduction was twofold (11.5%) as that of Pusa 1121 (5.2%).

Mode of action: Selective contact herbicide, with a short duration of activity.

Active chemical: Bensulfuron 100g/kg

Application rate: 2.0 kg ai / ha (+ 0.5 kg ai / ha)

Trade names: Herbadox, Prowl, Stomp.

Generic name: Machete Other trade names: Machete, Butataf, Butanex, Farmachlor,

Trade names: Whip

Application rate: 0.75 to 2.0 kg ai / ha