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Weed control in dry direct-seeded rice using tank mixtures of herbicides in South Asia
Crop Protection 72 (2015) 90e96
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Weed control in dry direct-seeded rice using tank mixtures of herbicides in South Asia G. Mahajan a, *, B.S. Chauhan b a b
Punjab Agricultural University, Ludhiana 141004, India Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Toowoomba 4350, Queensland, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 January 2015 Received in revised form 3 March 2015 Accepted 3 March 2015 Available online
Dry direct-seeded rice (DSR) faces with complex weed problems particularly when farmers missed preemergence herbicide applications. Thus, an effective and strategic weed control in DSR is often required with available options of post-emergence herbicides. In such situations, tank mixtures of herbicides may provide broad spectrum weed control in DSR. Field experiments were conducted in the wet seasons of 2013 and 2014 to study weed control in response to tank mixtures of herbicides currently applied in DSR in South Asia. Results revealed that the tank mixtures of the currently available herbicides (azimsulfuron plus bispyribac or fenoxaprop, bispyribac plus fenoxaprop, and azimsulfuron plus bispyribac plus fenoxaprop; all applied as post-emergence) rarely resulted in antagonistic effects. Highest weed control efficiency (~98%) was recorded with the tank mixture of azimsulfuron plus bispyribac plus fenoxaprop during both the years. This treatment also produced highest grain yield (7.2 t ha1 in 2013 and 7.9 t ha1in 2014), which was similar to the grain yield in the plots treated with the tank mix of azimsulfuron plus fenoxaprop, pendimethalin (applied as pre-emergence) followed by (fb) bispyribac, pendimethalin fb fenoxaprop, as well as pendimethalin fb azimsulfuron. Plots treated with the postemergence application of single herbicide (i.e., azimsulfuron, bispyribac, or fenoxaprop) had lower grain yield (3.0e5.2 t ha1 in 2013 to 3.5e6.1 t ha1in 2014) than all the sequential herbicide treatments and tank mixtures (azimsulfuron plus fenoxaprop and azimsulfuron plus bispyribac), owing to a broad spectrum weed control. The study suggested that if farmers missed the pre-emergence application of herbicides (e.g., pendimethalin) due to erratic rains or due to other reasons, good weed control and high yield can still be obtained with tank mix applications of azimsulfuron plus fenoxaprop or azimsulfuron plus bispyribac plus fenoxaprop in DSR. © 2015 Elsevier Ltd. All rights reserved.
Keywords: DSR North-west India Weed control Weed density Weed biomass Yield
1. Introduction Rice (Oryza sativa L.), being a staple food of more than half of the population of South Asia, is an important crop of India. In most parts of South Asia, rice is grown by transplanting of 25e30 days old seedlings into the puddled fields. Rice consumes a lot of water (~150 cm); out of which about 20e25 cm of water is used only for puddling purpose in transplanted rice (Mahajan et al., 2011). Water is a valuable and scarce natural resource in many regions of the world. Rice farmers in many areas in Asia are likely to have water scarcity for cultivating flooded rice in the future (Tuong and Bouman, 2003). Population projections for India revealed that per
* Corresponding author. E-mail address: [email protected] (G. Mahajan). http://dx.doi.org/10.1016/j.cropro.2015.03.002 0261-2194/© 2015 Elsevier Ltd. All rights reserved.
capita availability of water is expected to decrease from 1600 to 1000 m3 capita1 year1 by 2050 (Narula and Lall, 2010). It is also expected that agriculture's share of freshwater use will be reduced by 8e10% by 2025 because of increasing competition from the urban and industrial sectors (Gleick, 2000; Chauhan et al., 2012). Thus, water for cultivating rice will become increasingly difficult to obtain. This situation is worst in the north-west India, which is known as the food basket of India. A recent satellite survey revealed that the ground water table in north-west India is declining on an average at the rate of 0.33 m year1, and there is a net loss of 109 km3 of groundwater in northern India, double the capacity of India's largest surface reservoir (Rodell et al., 2009). Cultivation of rice in this region is blamed to be the major culprit for water scarcity because rice in this region is mainly cultivated through tubewell irrigation (i.e., underground mining of water). Puddled transplanted rice is cumbersome as well as energy and
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labour intensive. In the north-west India, due to ordinances (not to transplant paddy before 1st June) passed by some states, the window period (10e30th June) for rice planting has become narrow and there is a scarcity of labour because of huge demand, particularly at the time of transplanting. Delayed transplanting of rice in July not only causes reductions in rice yield (Mahajan et al., 2009) but also become an obstacle for the timely sowing of the subsequent wheat (Triticum aestivum L.) crop. This led to high wage rates at the time of rice transplanting because of limited labour availability. It has been observed that labour wages for rice transplanting during the past five years increased five times. Therefore, farmers in north-west India now have shown more interest in drydirect-seeded rice (DSR) as it helps in the timely planting of both rice and wheat. DSR increases profitability, requires less labour, water, and energy, and is more conducive to mechanisation. Despite several advantages of DSR, it is subjected to much higher weed pressure than the conventional puddled transplanted rice systems (Chauhan, 2012), in which weeds are suppressed by standing water and transplanted rice seedlings, which have a “headstart” over germinating weed seedlings (Moody, 1983). Aerobic soil conditions and alternate wetting and drying in DSR are conducive to the germination and growth of weeds, causing grain yield losses of up to 80% (Mahajan et al., 2009). Thus, an efficient and timely weed control is crucial for the success of DSR. In order to control weeds, farmers use both pre- and post-emergence herbicides (Mahajan et al., 2013; Mahajan and Timsina, 2011). Control of weeds through the application of pre-emergence herbicides (for instance, pendimethalin) is quite tricky. The time window for the application of pre-emergence herbicides is very narrow (usually 0e3 days of seeding) and it requires adequate moisture during the application time (Mahajan et al, 2013). Sometimes, farmers missed the optimum application time of preemergence herbicides due to onset of erratic rains at that time or due to other reasons. Weed flora in DSR is very complex and a single use of a pre- or post-emergence herbicide does not provide effective weed control in DSR (Mahajan et al., 2009). The use of herbicide combinations, whether the herbicides are applied simultaneously (tank-mixed) or sequentially, generally improves weed control compared with a single herbicide application (Mahajan and Timsina, 2011). Earlier, Mahajan and Chauhan (2013) revealed that sequential applications of pre- and post-emergence herbicides provided better weed control than the sole application of pre- or post-emergence herbicides in DSR. Among the post-emergence herbicides, bispyribac-sodium (bispyribac hereafter), azimsulfuron, and fenoxaprop-p-ethyl (fenoxaprop, hereafter) are widely used by the farmers in DSR. However, each herbicide provides selective weed control, for instance, bispyribac is effective mainly against Cyperus iria L. and azimsulfuron is effective mainly against Cyperus rotundus L. (Mahajan and Chauhan, 2013). Earlier, fenoxaprop without safener was used in DSR for the control of Leptochloa chinensis (L.) Nees and Dactyloctenium aegyptium (L.) Willd., but it also caused toxicity to the rice crop (Gopal et al., 2010). A new formulation of fenoxaprop (with isoxadifen, a safener), a relatively new herbicide in India, inhibits the synthesis of a majority of fatty acids in the meristem tissues of weeds by acting on ACCase within 1e2 weeks of application without any toxicity to the rice crop, depending on the environmental conditions. Isoxadifen reduces the foliar uptake of fenoxaprop in rice and accelerates its transformation into nonphytotoxic metabolites. According to Blouin et al. (2010), fenoxaprop provides excellent control of major grasses such as L. chinensis, D. aegyptium, Digitaria sanguinalis (L.) Scop., and Echinochloa colona (L.) Link. that are predominant in DSR fields. Because fenoxaprop does not have an activity on broadleaf weeds or sedges, it is likely that other herbicide(s) with an activity on broadleaf or
91
sedge weeds will be needed in a weed control program containing fenoxaprop in DSR. It would be beneficial in DSR to apply fenoxaprop plus another herbicide with broadleaf or sedge activity in a mixture, saving both time and cost. However, often broadleaf or sedge herbicides in a mixture with herbicides with grass activity, such as fenoxaprop, may antagonise or reduce the activity of the herbicide on grass weeds. Thus, the identification of compatibility of potential tank-mix herbicides with fenoxaprop is important in DSR. Such information will help DSR farmers to achieve broad spectrum of weed control. Research surveys at the farmers' fields revealed that control of complex weed flora with a single post-emergence herbicide application is really a difficult task for the DSR farmers (Mahajan et al., 2013, 2009). Undoubtedly, the development and availability of effective post-emergence herbicides have encouraged farmers to try this new method of crop establishment (DSR) in Asia. As a result, the area under DSR in the north-western part of the Indo-Gangetic Plains is increasing (Mahajan et al., 2013). However, the emergence of new and complex weed flora in DSR restricts the area expansion and sustainability of this crop establishment method. Literature suggests that the repeated use of the same herbicides encourages the problem of herbicide resistance in weeds (Kim, 1996). For a broad spectrum of weed control in DSR, applications of herbicides with different modes of action (chemistry) is needed. Applications of different herbicides as a tank mixture may prove helpful in delaying the problem of herbicide resistance as well as a shift in weed flora, which is invariably associated with the use of a single herbicide (Wrubel and Gressel, 1994). Diggle et al. (2003) in a specific modelling study revealed that; where the assumption of independent resistance are met, resistance to the mixture can only arise via the spontaneous evolution of resistance mechanisms to both (or all) mixture components. The likelihood of this mechanism decreases with each additional herbicide in the mixture (Wrubel and Gressel, 1994). Therefore, the combined application of different herbicides with different modes of action is required for broad spectrum weed control in DSR and for delaying the development of herbicide resistance. To the best of our knowledge, a very few studies in this line have been conducted in DSR grown in this region. Thus, it is essential to identify economic and effective herbicide combinations for managing complex weed flora in DSR. This study was conducted for generating detailed information for managing a mixed population of grass, sedge, and broadleaf weeds in DSR effectively and economically with tank mix applications of newly available postemergence herbicides. 2. Materials and methods 2.1. Experimental site A field study was conducted for two years (wet seasons of 2013 and 2014) at the research farm of Punjab Agricultural University, Ludhiana (30.93 N, 75.86 E), India. The climate is semiarid, with an average annual rainfall of 400e700 mm (75e80% of which is received from July to September), a minimum temperature of 0e4 C in January, and a maximum temperature of 41e45 C in June. The soil type at the experimental site was Fatehpur Series sandy loam (Entisol, Typic Ustipsament) with 0.3% organic matter with a pH of 7.2. Groundwater depth at the site was below 25 m, and the water was non-saline. 2.2. Experimental design and treatments The treatments in each year were arranged in a randomised complete block design with three replications. Twelve weed control
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treatments were included to evaluate different herbicide options for weed control in DSR (Table 1). Herbicides included in the study were pendimethalin (Stomp, BASF India Ltd.), bispyribac-sodium (Nominee gold, PI Industries), azimsulfuron (Segment, Dupont India Ltd.), and fenoxaprop (Rice star, Bayer, India).
are reported with interpretation based on transformed data. Relationships between grain yield and weed biomass were assessed using linear regression analysis (Sigma Plot 10.0). Since, every penny has a value for farmers; no statistical analysis was done for additional net return in response to herbicide use.
2.3. Experimental details and measurements
3. Results and discussion
In each year, rice (cv. PR-115, a cultivar with duration of 120 d) was seeded in the last week of June and harvested in October. Fields were prepared by cultivating twice with a disc harrow, followed by levelling with a wooden board. Seeds were sown with a single-row drill at a seeding rate of 25 kg ha1 at 20-cm row spacing. The size of the plots was 5.5 m by 2.0 m. The field was surface irrigated immediately after sowing, so that it may have enough moisture at the time of pendimethalin (pre-emergence herbicide) application. Nitrogen (150 kg ha1) was applied in four equal splits at 15, 30, 45, and 60 d after sowing (DAS). Recommended rates of chlorpyriphos (500 g ai ha1, Chlorguard, Gharda Chemical Ltd.) and propiconazole (62.5 g ai ha1, Tilt, Syngenta India Ltd.) were used to control insects and diseases. Pre-emergence (PRE) herbicides were applied at 3 DAS and post-emergence (POST) herbicides were applied at 25 DAS. Herbicides were applied with the use of a knapsack sprayer fitted with a flat-fan nozzle and water as a carrier at 500 L ha1 for pre-emergence spray and at 375 L ha1 for post-emergence spray. Species-wise density and total biomass of weeds were measured at maturity. Weed density was recorded in two quadrats (0.5 m by 0.4 m) placed randomly in each plot. Weeds were cut at ground level, washed with tap water, sun-dried, oven-dried at 70 C for 48 h, and then weighed. Grain yield was measured form an area of 7.2 m2 in the centre of each plot and expressed in t ha1 at14% moisture. Weed control efficiency (WCE, %) was calculated using the formula
3.1. Weed density and biomass
WCE ¼ ðweed biomass in non treated plot weed biomass in treated plotÞ= ðweed biomass in non treated plotÞ 100
2.4. Statistical analyses Data generated from the experiments were analysed using GenStat V.10 and mean comparisons were performed based on the least significant difference (LSD) test at 0.05 probability. Weed density data were transformed using square-root transformation [√(xþ1)] before analyses. The non-transformed weed density data
Table 1 Herbicide treatments used in the study. Herbicide treatments
Dose (g a.i. ha1)
Application time (days after sowing)
Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuronplusbispyribac Bispyribacplusfenoxaprop Azimsulfuronplusfenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop
e 750 25 20 67.5 15plus 18.7 18.7 plus50.6 15plus50.6 750 fb 25 750 fb 67.5 750 fb 20 15plus 18.7plus 50.6
e 3 20 20 20 20 20 3 fb 3 fb 3 fb 3 fb 20
Abbreviations: fb ¼ followed by.
20 20 20 20
The experimental plots contained C. iria, C. rotundus, D. aegyptium, D. sanguinalis, L. chinensis, Echinochloa colona, Eleusine indica, Digera arvensis, Ludwigia octovalvis, Panicum brevifolium, Euphorbia spp., Eragrostis pilosa, etc. However, species-wise results are presented for the first six weeds only, as they were dominant in the samples. 3.1.1. C. iria and C. rotundus The data for C. iria and C. rotundus were combined as our emphasis was more on Cyperus spp. rather than on individual species. The tank mix application of azimsulfuron plus bispyribac plus fenoxaprop significantly reduced the density of sedges (C. iria and C. rotundus) compared with the non-treated control (Table 2). Sedge densities in the plots treated with pendimethalin, bispyribac, and fenoxaprop individually were 32, 5, and 29 plants m2 in 2013 and 21, 11, and 23 plants m2 in 2014 compared with 36 and 28 plants m2 in the non-treated plots in 2013 and 2014, respectively. No sedge plants were observed in the plots treated with the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop, azimsulfuron alone, and pendimethalin fb bispyribac or azimsulfuron. The application of pendimethalin and fenoxaprop sole, and pendimethalin fb fenoxprop provided similar density of sedges as in the non-treated plots. Sedge density with tank mix application of azimsulfuron plus bispyribac, bispyribac plus fenoxaprop, and azimsulfuron plus fenoxaprop was similar to that with the application of bispyribac (5 plants m2 in 2013 and 11 plants m2 in 2014). Pendimethalin and fenoxaprop were ineffective against sedges. However, the application of bispyribac and azimsulfuron controlled sedges effectively when applied alone or tank mixed. The superiority of azimsulfuron compared to bispyribac against sedges was due to the combined occurrence of C. rotundus and C. iria in the field. Mahajan and Chauhan (2013) revealed that azimsulfuron was more effective against C. rotundus as compared to bispyribac. In the present studies, the application of azimsulfuron provided complete control of sedges (C. rotundus and C. iria). The results also suggested a poor control of the two sedges by fenoxaprop. Tank mix application of azimsulfuron plus bispyribac did not provide 100% control of sedges as with sole application of azimsulfuron in 2014. This might be due to some degree of antagonistic effect that provided relatively lower control of C. rotundus as compared to azimsulfuron. It is quite possible that antagonistic effect of these herbicides varied with the weather condition, as tank mix application of azimsulfuron plus bispyribac and sole application of azimsulfuron provided similar control of sedges during the first year of study. 3.1.2. D. aegyptium The lowest density of D. aegyptium (Table 2) was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (1.3 plants m2 in 2013 and 0 plants m2 in 2014). D. aegyptium density observed following the application of pendimethalin was 13 and 8 plants m2 compared with 33 and 28 plants m2 in the non-treated control in 2013 and 2014, respectively. In both years, the application of bispyribac, azimsufuron, and tank mixture of azimsulfuron plus bispyribac resulted in similar
(143) (51) (70) (61) (57) (67) (30) (32) (14) (33) (19) (3) Abbreviations: fb ¼ followed by.
2014
11.9 7.21 8.40 7.88 7.60 8.21 5.39 5.70 3.83 5.71 4.42 1.67 1.77 (174) (74) (79) (60) (65) (73) (34) (37) (29) (53) (23) (5) 13.1 8.65 8.86 7.74 8.09 8.60 5.70 6.09 5.51 7.29 4.72 2.33 2.07
2013 2014
5.82 (33) 2.33 (5) 1.41 (1) 1.82 (3) 3.40 (11) 1.41 (1) 2.61 (8) 2.53 (7) 1 (0) 2.61 (8) 30 (8) 1.67 (3) 1.53 3.98 (15) 1.71 (2) 3.60 (12) 3.60 (12) 1.27 (1) 3.60 (12) 1.28 (10) 1.13 (0) 1.62 (2) 1 (0) 1.27 (1) 1 (0) 0.39
6.35 3.20 2.49 1.41 4.10 2.53 3.11 3.32 2.49 3.13 3.40 2.08 1.72
(40) (9) (5) (1) (16) (7) (9) (11) (5) (12) (11) (4)
2013 2013
4.02 (15) 1.71 (2) 3.69 (13) 3.60 (12) 1.14 (0) 3.69 (13) 1.13 (0) 1.13 (0) 1.52 (1) 1 (0) 1.14 (0) 1 (0) 0.43
2014
4.10 (16) 3.0 (8) 1.82 (3) 1.82 (3) 2.08 (4) 1.82 (3) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 0.83 4.41 (19) 2.74 (7) 2.08 (4) 2.08 (4) 2.08 (4) 1.82 (3) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1.01
2013 2014
4.66 (23) 2.53 (7) 4.71 (22) 4.88 (24) 3.60 (12) 5.01 (25) 2.04 (5) 2.94 (8) 1 (0) 1.41 (1) 2.53 (7) 1 (0) 1.89 5.26 (29) 3.32 (11) 5.12 (27) 4.53 (23) 3.20 (9) 4.57 (21) 3.06 (11) 2.93 (8) 2.24 (4) 2.49 (5) 2.53 (7) 1 (0) 1.98
2013 2014
5.25 (28) 2.73 (8) 4.68 (22) 4.53 (20) 2.82 (7) 4.78 (23) 3.20 (9) 3.58 (12) 3.60 (12) 1.82 (3) 2.08 (4) 1 (0) 1.54 (33) (13) (25) (20) (6) (27) (9) (13) (19) (5) (5) (1.33) 5.73 3.64 5.03 4.49 2.54 5.24 3.12 3.64 4.42 2.49 2.28 1.41 1.69
2013 2014
3.1.3. D. sanguinalis D. sanguinalis density in the non-treated control was 29 and 23 plants m2 in 2013 and 2014, respectively (Table 2). In both years, the lowest density of D. sanguinalis was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (~0 plants m2) and it was similar to the density in all the sequential herbicide treatments tested [i.e., pendimethalin fb bispyribac, pendimethalin fb azimsulfuron, and pendimethalin fb fenoxaprop]. The application of bispyribac, azimsulfuron, and tank mix of azimsulfron plus bispyribac provided density of D. sanguinalis similar to that in non-treated control. The application of fenoxaprop reduced the density of D. sanguinalis (9 and 12 plants m2 respectively in 2013 and 2014) as compared to then on-treated control (29 and 23 plants m2 in 2013 and 2014). The D. sanguinalis density in the pendimethalin-treated plots was 11 and 7 plants m2 in 2013 and 2014, respectively. Our results revealed that the sequential application of pendimethalin fb fenoxaprop reduced the density of D. sanguinalis by 83 and 96% during 2013 and 2014, respectively. However, a complete control (~100%) was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop due to vigorous growth of crop that did not allow later flush of D. sanguinalis. In a recent study, bispyribac provided poor control (30e40%) of D. ciliaris (Chauhan and Abugho, 2012). Similarly in another study, Mahajan and Chauhan (2013) revealed that azimsufuron was not effective in controlling D. sanguinalis.
5.36 (28) 4.71 (21) 3.40 (11) 1 (0) 4.78 (23) 2.33 (5) 2.74 (7) 2.28 (5) 1 (0) 4.66 (21) 1 (0) 1 (0) 1.17
2013
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D. aegyptium density as observed in the non-treated control. The application of fenoxaprop (6 plants m2 in 2013 and 7 plants m2 in 2014), tank mix of bispyribac plus fenoxaprop (9 plants m2 each in 2013 and 2014), and azimsulfuron plus fenoxaprop (13plants m2 in 2013 and 12 plants m2 in 2014) resulted in similar D. aegyptium density; however, these densities were lower than those in the non-treated control. D. aegyptium density following the tank mix application of azimsulfuron plus fenoxaprop and bispyribac plus fenoxaprop was higher than that following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop, mainly because of the appearance of late emerging seedlings of D. aegyptium. The rice crop following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop was almost weed-free and did not allow the later flush of weed seedlings to grow due to vigorous growth of the crop. Mahajan and Chauhan (2013) in an earlier study revealed that the single application of azimsulfuron and bispyribac did not control D. aegyptium.The sequential application of pendimethalin fb azimsulfuron proved superior in controlling D. aegyptium. Because, this treatment was quite effective against C. rotundus, thus helped the crop in attaining vigorous growth at the initial stage of the crop that in turn provided smothering effect on D. aegyptium.
6.07 (36) 5.69 (32) 2.49 (5) 1 (0) 5.46 (29) 1.41 (1.33) 2.24 (4) 2.0 (5) 1 (0) 5.60 (31) 1 (0) 1 (0) 1.22 Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuron plus bispyribac Bispyribac plus fenoxaprop Azimsulfuron plus fenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop LSD (0.05)
2014
Other weeds Leptochloa chinensis Echinochloa colona Digitaria sanguinalis Dactyloctenium aegyptium Cyperus spp.
Weed count (no.m2) Herbicide treatments
Table 2 Effect of treatments on weed density (number m2) at maturity. Square-root transformed [ ¼ √(xþ1)] values were used for analyses and original weed density values are shown in parentheses.
Total weed count
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3.1.4. E. colona The density of E. colona in the non-treated control was 19 and 16 plants m2 during 2013 and 2014, respectively (Table 2). All the tested herbicide treatments reduced the density of E. colona as compared to the non-treated control. The lowest density of E. colona (0 plant m2) was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop and it was similar to all the other sequential and tank mix herbicide treatments. The application of azimsulfuron, bispyribac, and fenoxaprop provided similar density of E. colona and proved effective in reducing its density compared with the non-treated control. Our findings showed that almost all the tested herbicides were effective for the control of E. colona; however, the control was better when herbicides were applied as a tank mix or
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in sequential applications (pre-emergence fb post-emergence). This study also revealed that relatively pendimethalin and fenoxaprop-prop were less effective against E. colona as compared to bispyribac and azimsulfuron. 3.1.5. L. chinensis The density of L. chinensis in the non-treated control was 15 plants m2 during both the years (Table 2). Bispyribac, azimsulfuron, and the tank mixture of azimsulfuron plus bispyribac had L. chinensis density similar to the non-treated control. All the other herbicide combinations proved effective in controlling this weed. An earlier study revealed that bispyribac and azimsulfuron were ineffective against L. chinensis (Mahajan and Chauhan, 2013). 3.1.6. Other weeds The density of other weeds in the non-treated control plot was 40 and 33 plants m2 in 2013 and 2014, respectively (Table 2). All herbicide treatments reduced the density of other weeds significantly as compared to the non-treated control. Density of other weeds following the application of fenoxaprop was 16 and 11 plants m2 in 2013 and 2014, respectively, and it was higher than in the azimsulfuron-treated plots (1 and 3 plant m2 in 2013 and 2014, respectively).
with the sequential applications of pendimethalin fb fenoxaprop (64.3e67.2 g m2) and pendimethalin fb bispyribac (62.5e74.4 g m2). Total weed biomass in the tank mix applications of azimsulfuron plus fenoxaprop (76.7 g m2 in 2013 and 98 g m2 in 2014) and bispyribac plus fenoxaprop (151.8 g m2 in 2013 and 164.3 g m2 in 2014) was similar during 2013 and 2014. The tank mixture of azimsulfuron plus fenoxaprop showed superiority for weed control as compared to the single application of bispyribac and azimsulfuron. These results suggest that tank mixing of azimsulfuron plus fenoxaprop might have greater synergistic effect for broad spectrum weed control as total weed biomass was lower than that in the plots treated with single applications of herbicides. The effect was more pronounced when this combination was again mixed with bispyribac and provided excellent broad spectrum weed control. Blouin et al. (2010) found that mixtures of ALSinhibitor herbicides with fenoxaprop, if applied in optimum doses, enabled greater weed control in rice. Similarly in another study, Leon et al. (2002) revealed that Ricestar (fenoxaprop-P-ethyl plus safener) tank-mixed with Arrosolo (propanil plus molinate) applied at mid post-emergence (35 days after sowing) controlled E. colona, Leptochloa panicoides (Presl) Hitchc., and broadleaf Brachiaria platyphylla (Griseb.) Nash by 88e95%. 3.2. Grain yield response
3.1.7. Total weed density Total weed density in the non-treated control plot was 174 and 133 plants m2 in 2013 and 2014, respectively (Table 2). All herbicide treatments reduced the total weed density significantly as compared to the non-treated control. The lowest total weed density was observed after the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (5 plants m2 in 2013 and 3 plants m2in 2014). Total weed density following the single application of pendimethalin was 74 and 51 plants m2 in 2013 and 2014, respectively, and it was similar to that for the tank mix of azimsulfuron plus bispyribac (73 plants m2 in 2013 and 67 plants m2 in 2014). Total weed density following the tank mix application of herbicides was lower than pendimethalin alone. Total weed density following the single application of azimsulfuron, bispyribac, and fenoxaprop was similar to the density in the pendimethalin-treated plots. Among the sequential herbicide treatments, total weed density in the plots treated with pendimethalin fb bispyribac and pendimethalin fb azimsulfuron was similar in both years; however, lower than non-treated control. 3.1.8. Total weed biomass Total weed biomass in the non-treated control was 421.7 and 410.3 g m2 in 2013 and 2014, respectively (Table 3). All herbicide treatments significantly reduced weed biomass compared to the non-treated control in both years, except pendimethalin in 2013 (Table 4). Weed control efficiency with single herbicide applications ranged from 19 to 53% in 2013 and 27e59% in 2014; with tank mixture of two herbicides ranged from 35 to 82% in 2013 and 54e76% in 2014; with sequential spray varied from 73 to 85% in 2013 and 27e59% in 2014. Weed biomass following a single application of bispyribac, fenoxaprop, and azimsulfuron was similar. Compared with the non-treated control, the sole application of these three herbicides, respectively, reduced weed biomass by 53.4, 52.9, and 53.2% in 2013, and 55.2, 54.4, and 58.9% in 2014. In both years, these treatments also reduced total weed biomass greater than that after pendimethalin application. The lowest weed biomass (8.5 and 5.6 g m2 in 2013 and 2014, respectively) and highest weed control efficiency (~98%) was observed in the plots treated with tank mix application of azimsulfuron plus bispyribac plus fenoxaprop. Biomass in these plots, however, was similar to the biomass produced in the plots treated
Rice grain yield following all herbicide treatments ranged from 2.96 e 7.23 t ha1and 3.46 e 7.86 t ha1, while the non-treated plots yielded 1.92 and 2.67 t ha1 in 2013 and 2014, respectively (Table 3). The highest grain yield was recorded in the plots treated with the tank mix of azimsulfuron plus bispyribac plus fenoxaprop (7.23 t ha1 in 2013 and 7.86 t ha1in 2014) and it was similar to the yield observed in the plots treated with the tank mix of azimsulfuron plus fenoxaprop, pendimethalin fb bispyribac, pendimethalin fb fenoxaprop, and pendimethain fb azimsulfuron. In both years, grain yield in the plots treated with azimsulfuron (4.49 t ha1in 2013 and 5.38 t ha1 in 2014), bispyribac (4.67 t ha1 in 2013 and 5.31 t ha1 in 2014), and fenoxaprop (5.21 t ha1 in 2013 and 6.10 t ha1 in 2014) was similar, but greater than the grain yield recorded in the pendimethalin-treated plots. Plots treated with the single herbicide (azimsulfuron, bispyribac, or fenoxaprop) had lower grain yield compared to all the sequential spray treatments and tank mixed applications of azimsulfuron plus fenoxaprop and azimsulfuron plus bispyribac plus fenoxaprop. Grain yield in the plots treated with azimsulfuron plus bispyribac, bispyribac alone, and azimsulfuron alone were similar. Among herbicide treatments, the lowest grain yield was observed in the plots treated with pendimethalin, owing to a high weed pressure experienced by the crop. As expected, the correlation of weed biomass and grain yield was negative in the present study. Weed biomass accounted for 96% and 93% variation in grain yield during 2013 and 2014, respectively (Fig. 1). It was observed that weeds, namely E. colona, L. chinensis, D. sanguinalis, and D. aegyptium appeared in the field in several flushes. Although total weed density decreased from 174 to 74 plants m2 and 143 to 51 plants m2 after the pendimethalin application as compared to the non-treated control in 2013 and 2014, respectively, weed biomass was merely reduced by19%in 2013 and 27% in 2014 after this herbicide treatment. These results indicate that weeds posed high competition to the crop for water, nutrient, and light, causing poor crop growth and resulted in lower grain yield in the pendimethalin-treated plots compared to other herbicide treatments. Grain yield in the single herbicide-treated plots was similar because of similar weed pressure, in terms of weed biomass faced by the crop. Weed density data revealed that azimsulfuron and
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Table 3 Effect of herbicide treatments on paddy grain yield (t ha1) and weed biomass (g m2) at maturity. Herbicide treatments
Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuron plus bispyribac Bispyribac plus fenoxaprop Azimsulfuron plus fenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop LSD (0.05)
Total weed dry matter (g m2)
Weed control efficiency (%)
Grain yield (t ha1)
2013
2014
2013
2014
2013
2014
421.7 341.3 196.3 198.3 197.3 272.7 151.8 76.7 74.4 64.3 115.2 8.5
410.3 300.3 183.5 187.0 168.3 190.0 164.3 98.0 62.5 67.2 110.0 5.67
e 19.1 53.4 53.0 53.2 35.3 64.0 81.8 82.3 84.7 72.7 98
e 26.8 55.3 54.4 59.0 53.7 60.0 76.1 84.8 83.6 73.2 98.6
1.92 2.96 4.67 4.49 5.21 4.58 5.36 6.56 6.79 6.85 6.57 7.23
2.67 3.46 5.31 5.38 6.10 4.88 6.49 7.32 7.24 7.46 7.24 7.86
100.4
79.6
e
e
0.7
0.8
Abbreviations: fb ¼ followed by.
bispyribac were quite effective in controlling sedges. A single application of fenoxaprop failed to control sedges; however, it caused a drastic reduction in the density of L. chinensis, D. aegyptium, and D. sanguinalis. Therefore, overall total weed density and biomass remained similar with the application of a single herbicide, resulting in similar grain yield. Among the tank mix herbicide treatments, azimsulfuron plus bispyribac provided lower yield due to poor control of L. chinensis, D. aegyptium, and D. sanguinalis. Average of the two-year mean data showed that total weed biomass reduced by 32, 62, and 97% when fenoxaprop was tank mixed with bispyribac, azimsulfuron, and both azimsulfuron plus bispyribac, respectively, as compared to the tank mix application of azimsulfuron plus bispyribac. It means L. chinensis, D. aegyptium, and D. sanguinalis offered great competition to the crop and their control with fenoxaprop helped in increasing the yield. All sequential herbicide treatments resulted in similar yield because of similar weed biomass observed in each plot. The highest grain yield following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop was due to the lowest weed biomass observed in the crop. The synergistic effect of these herbicides in tank mixing provided excellent weed control. It was observed that the rice crop faced weed competition before the spray of the tank
mixture of azimsulfuron plus bispyribac plus fenoxaprop. However, after the spray of this tank mixture, crop grew vigorously and did not allow the later flushes of weeds to grow, resulting in the highest yield. Therefore, the present study showed that the azimsulfuron plus bispyribac plus fenoxaprop treatment resulted in an additive response for weed control. Christopher et al. (2005) also reported that fenoxaprop plus bentazon or propanil plus molinate resulted in an additive response for E. colona control. This study revealed that when ACCase inhibitor herbicides are used at substantially lower than labelled rates in combination with ALS inhibitors, the activity of the combination is superior to the components when used alone. Furthermore, there are no antagonistic effects, in fact, the effect is synergistic. This synergistic effect will broaden the options for economic weed control for DSR farmers by allowing for a wider application window (greater flexibility in timing of application) and broader spectrum of weed control, such as control of hardy grass weeds (L. chinensis, D. aegyptium, and D. sanguinalis); not normally controlled by bispyribac and azimsulfuron. 3.3. Economics Additional costs due to herbicide treatments varied from 24.6 to 60.4 USD ha1; lowest with pendimethalin and highest with the
Table 4 Additional cost and net profit ($) occurred in response to herbicide use. Herbicide treatments
Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuron plus bispyribac Bispyribac plus fenoxaprop Azimsulfuron plus fenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop
Additional cost of herbicide (USD ha1)
24.6 27.1 28.5 25 41.7 39.0 40.2 53.1 49.6 53.1 60.4
Additional income with herbicide use (USD ha1)
Additional net profit with herbicide use (USD ha1)
2013
2014
2013
2014
242.7 641.7 599.7 767.7 620. 802.7 1082.7 1136.3 1150.3 1061.7 1239
184.3 616 632.3 800.3 515.7 891.3 1085 1066.3 1117.7 1066.3 1211
218.1 614.6 571.1 742.7 579.0 763.6 1042.5 1083.2 1100.7 1008.5 1178.5
159.7 588.9 603.8 775.3 473.9 852.3 1044.8 1013.2 1068.1 1013.2 1150.5
Abbreviations: fb ¼ followed by. Price of paddy 233.3 USD t1; Cost of herbicides (Pendimethalin- 9.83 USD litre1; Azimsulfuron 71.3 USD 100 g1; Bispyribac 108.3 USD litre1; fenoxaprop e 25 USD litre1); 1 USD (US dollar) ¼ 60 Indian Rupees.
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plots treated with the tank mixture of azimsulfuron plus bispyribac plus fenoxaprop recorded highest yield because of lowest weed biomass in these plots. Our study thus demonstrated that the sequential applications of pre- and post-emergence herbicides are needed for maintaining good weed control and yield in DSR. Somehow, if farmers missed the application of pre-emergence herbicides (e.g., pendimethalin) due to erratic rains or other reasons, effective weed control and high yield can still be obtained with the tank mix application of azimsulfuron plus fenoxaprop or azimsulfuron plus bispyribac plus fenoxaprop. Tank mix application of azimsulfuron plus bispyribac plus fenoxaprop provided complete control of sedges especially C. iria and C. rotundus, grass and broadleaf weeds with weed control efficiency ~98%.Among the herbicide treatments, the profitability was highest after the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop. Thus, a synergistic composition of azimsulfuron plus bispyribac plus fenoxaprop, when applied to DSR, allows a reduction in the amount of herbicide needed, greater flexibility in timing of the application besides offering broad spectrum weed control.
References
Fig. 1. Relationship between weed biomass (g m2) and grain yield (t ha1) during 2013 (a) and 2014 (b).
tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (Table 4). With the single herbicide application, the cost varied from 24.6 to 28.5 USD ha1 and it was highest for azimsulfuron. The herbicide cost with the tank mix application of two herbicides ranged from 39.0 to 41.7 USD ha1. In sequential herbicide treatments, herbicide cost varied from 49.6 to 53.1 USD ha1. Additional net profit (1179 and 1151 USD ha1 in 2013 and 2014, respectively) was highest with the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop. The application of pendimethalin provided additional net profit, amounting to 218 and 160 USD ha1 in 2013 and 2014, respectively. With the application of single herbicide, additional profit due to herbicide use varied from 571 e 743 and 589- 775 USD ha1 in 2013 and 2014, respectively; highest with fenoxaprop. Among the tank mixed herbicide treatments, additional profit of greater than 1000 USD ha1 was observed with azimsulfuron plus fenoxaprop (1043 USD ha1 in 2013 and 1045 USD ha1 in 2014) and azimsulfuron plus bispyribac plus fenoxaprop (1179 USD ha1 in 2013 and 1151USD ha1 in 2014). Additional net profit with the tank mix application of azimsulfuron plus bispyribac was lower than the single application of herbicides in both years. With the sequential herbicide treatments, additional profit due to herbicide use varied from 1009 to 1101 USD ha1 and 1013e1068 USD ha1 in 2013 and 2014, respectively. 4. Conclusions A single application of herbicide (pre- or post-emergence) did not control the complex weed flora in DSR. Weed biomass and grain yield significantly improved when fenoxaprop was tank mixed with azimsulfuron. The sequential application of pendimethalin fb azimsulfuron, bispyribac, or fenoxaprop provided better weed control than the single application of any of these herbicides. The
Blouin, D.C., Webster, E.P., Bond, J.P., 2010. On a method of analysis for synergistic and antagonistic joint-action effects with fenoxaprop mixtures in rice (Oryza sativa). Weed Technol. 24, 583e589. Chauhan, B.S., 2012. Weed ecology and weed management strategies for dryseeded rice in Asia. Weed Technol. 26, 1e13. Chauhan, B.S., Abugho, S.B., 2012. Effect of growth stage on the efficacy of postemergence herbicides on four weed species of direct-seeded rice. Sci. World J. 7. Article ID 123071. Chauhan, B.S., Mahajan, G., Sardana, V., Timsina, J., Jat, M.L., 2012. Productivity and sustainability of the riceewheat cropping system in the Indo- Gangetic Plains of the Indian subcontinent: problems, opportunities, and strategies. Adv. Agron. 117, 315e369. Christopher, L.T., Blouin, D.C., Webster, E.P., 2005. Fenoxaprop interactions for barnyardgrass (Echinochloa crus-galli) control in rice. Weed Technol. 19,293e297. Diggle, A., Neve, P.B., Smith, F.P., 2003. Herbicides used in combination can reduce the probability of herbicide resistance in finite weed populations. Weed Res. 43, 371e382. Gleick, P.H., 2000. The World's Water 2000e2001. Biennial Report on Freshwater Resources. Island Press, Washington, DC. Gopal, R., Jat, R.K., Malik, R.K., Kumar, V., Alam, M.M., Jat, M.L., Mazid, M.A., Saharawat, Y.S., McDonald, A., Gupta, R., 2010. Direct Dry Seeded Rice Production Technology and Weed Management in Rice Based Systems. Technical Bulletin. International Maize and Wheat Improvement Center, New Delhi, India, p. 28. Kim, K.U., 1996. Ecological forces influencing weed competition and herbicide resistance. In: Naylor, R. (Ed.), Herbicides in Asian Rice: Transitions in Weed Management. Stamford University, California and IRRI, Philippines, pp. 129e142. Leon, C.T., Webster, E.P., Zhang, W., Pellerin, K.J., 2002. Grass control with Ricestar plus broadleaf herbicide tank-mixtures. Proc. Louis. Plant Prot. Assoc. 12, 69. Mahajan, G., Chauhan, B.S., 2013. Herbicide options for weed control in dry-seeded aromatic rice in India. Weed Technol. 27, 682e689. Mahajan, G., Timsina, J., 2011. Effect of nitrogen rates and weed control methods on weeds abundance and yield of direct-seeded rice. Arch. Agron. Soil Sci. 57, 239e250. Mahajan, G., Chauhan, B.S., Johnson, D.E., 2009. Weed management in aerobic rice in northwestern Indo-Gangetic Plains. J. Crop Improv. 4, 366e382. Mahajan, G., Timsina, J., Singh, K., 2011. Performance and water use efficiency of rice relative to establishment methods in northwestern Indo-Gangetic Plains. J. Crop Improv. 25, 597e617. Mahajan, G., Chauhan, B.S., Gill, M.S., 2013. Dry-seeded rice culture in Punjab state of India: lesson learned from farmers. Field Crops Res. 144, 89e99. Moody, K., 1983. The status of weed control in Asia. FAO Plant Prot. Bull. 30, 119e123. Narula, K.K., Lall, U., 2010. Challenge in securing India's water future. J. Crop Improv. 24, 85e91. Rodell, M., Velicigna, I., Famiglietti, J.S., 2009. Satellite-based estimates of groundwater depletion in India. Nat. Lond. 460, 999e1002. Tuong, T.P., Bouman, B.A.M., 2003. Rice production in water scarce environments. In: Kijne, J.W., Barker, R., Molden, D. (Eds.), Water Productivity in Agriculture: Limits and Opportunities for Improvement, vol. 53e67. IRRI, Philippines (CABI Publishing). Wrubel, R.P., Gressel, J., 1994. Are herbicide mixtures useful for delaying the rapid evolution of resistance? A case study. Weed Technol. 8, 635e648.
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Weed control in dry direct-seeded rice using tank mixtures of herbicides in South Asia G. Mahajan a, *, B.S. Chauhan b a b
Punjab Agricultural University, Ludhiana 141004, India Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Toowoomba 4350, Queensland, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 January 2015 Received in revised form 3 March 2015 Accepted 3 March 2015 Available online
Dry direct-seeded rice (DSR) faces with complex weed problems particularly when farmers missed preemergence herbicide applications. Thus, an effective and strategic weed control in DSR is often required with available options of post-emergence herbicides. In such situations, tank mixtures of herbicides may provide broad spectrum weed control in DSR. Field experiments were conducted in the wet seasons of 2013 and 2014 to study weed control in response to tank mixtures of herbicides currently applied in DSR in South Asia. Results revealed that the tank mixtures of the currently available herbicides (azimsulfuron plus bispyribac or fenoxaprop, bispyribac plus fenoxaprop, and azimsulfuron plus bispyribac plus fenoxaprop; all applied as post-emergence) rarely resulted in antagonistic effects. Highest weed control efficiency (~98%) was recorded with the tank mixture of azimsulfuron plus bispyribac plus fenoxaprop during both the years. This treatment also produced highest grain yield (7.2 t ha1 in 2013 and 7.9 t ha1in 2014), which was similar to the grain yield in the plots treated with the tank mix of azimsulfuron plus fenoxaprop, pendimethalin (applied as pre-emergence) followed by (fb) bispyribac, pendimethalin fb fenoxaprop, as well as pendimethalin fb azimsulfuron. Plots treated with the postemergence application of single herbicide (i.e., azimsulfuron, bispyribac, or fenoxaprop) had lower grain yield (3.0e5.2 t ha1 in 2013 to 3.5e6.1 t ha1in 2014) than all the sequential herbicide treatments and tank mixtures (azimsulfuron plus fenoxaprop and azimsulfuron plus bispyribac), owing to a broad spectrum weed control. The study suggested that if farmers missed the pre-emergence application of herbicides (e.g., pendimethalin) due to erratic rains or due to other reasons, good weed control and high yield can still be obtained with tank mix applications of azimsulfuron plus fenoxaprop or azimsulfuron plus bispyribac plus fenoxaprop in DSR. © 2015 Elsevier Ltd. All rights reserved.
Keywords: DSR North-west India Weed control Weed density Weed biomass Yield
1. Introduction Rice (Oryza sativa L.), being a staple food of more than half of the population of South Asia, is an important crop of India. In most parts of South Asia, rice is grown by transplanting of 25e30 days old seedlings into the puddled fields. Rice consumes a lot of water (~150 cm); out of which about 20e25 cm of water is used only for puddling purpose in transplanted rice (Mahajan et al., 2011). Water is a valuable and scarce natural resource in many regions of the world. Rice farmers in many areas in Asia are likely to have water scarcity for cultivating flooded rice in the future (Tuong and Bouman, 2003). Population projections for India revealed that per
* Corresponding author. E-mail address: [email protected] (G. Mahajan). http://dx.doi.org/10.1016/j.cropro.2015.03.002 0261-2194/© 2015 Elsevier Ltd. All rights reserved.
capita availability of water is expected to decrease from 1600 to 1000 m3 capita1 year1 by 2050 (Narula and Lall, 2010). It is also expected that agriculture's share of freshwater use will be reduced by 8e10% by 2025 because of increasing competition from the urban and industrial sectors (Gleick, 2000; Chauhan et al., 2012). Thus, water for cultivating rice will become increasingly difficult to obtain. This situation is worst in the north-west India, which is known as the food basket of India. A recent satellite survey revealed that the ground water table in north-west India is declining on an average at the rate of 0.33 m year1, and there is a net loss of 109 km3 of groundwater in northern India, double the capacity of India's largest surface reservoir (Rodell et al., 2009). Cultivation of rice in this region is blamed to be the major culprit for water scarcity because rice in this region is mainly cultivated through tubewell irrigation (i.e., underground mining of water). Puddled transplanted rice is cumbersome as well as energy and
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labour intensive. In the north-west India, due to ordinances (not to transplant paddy before 1st June) passed by some states, the window period (10e30th June) for rice planting has become narrow and there is a scarcity of labour because of huge demand, particularly at the time of transplanting. Delayed transplanting of rice in July not only causes reductions in rice yield (Mahajan et al., 2009) but also become an obstacle for the timely sowing of the subsequent wheat (Triticum aestivum L.) crop. This led to high wage rates at the time of rice transplanting because of limited labour availability. It has been observed that labour wages for rice transplanting during the past five years increased five times. Therefore, farmers in north-west India now have shown more interest in drydirect-seeded rice (DSR) as it helps in the timely planting of both rice and wheat. DSR increases profitability, requires less labour, water, and energy, and is more conducive to mechanisation. Despite several advantages of DSR, it is subjected to much higher weed pressure than the conventional puddled transplanted rice systems (Chauhan, 2012), in which weeds are suppressed by standing water and transplanted rice seedlings, which have a “headstart” over germinating weed seedlings (Moody, 1983). Aerobic soil conditions and alternate wetting and drying in DSR are conducive to the germination and growth of weeds, causing grain yield losses of up to 80% (Mahajan et al., 2009). Thus, an efficient and timely weed control is crucial for the success of DSR. In order to control weeds, farmers use both pre- and post-emergence herbicides (Mahajan et al., 2013; Mahajan and Timsina, 2011). Control of weeds through the application of pre-emergence herbicides (for instance, pendimethalin) is quite tricky. The time window for the application of pre-emergence herbicides is very narrow (usually 0e3 days of seeding) and it requires adequate moisture during the application time (Mahajan et al, 2013). Sometimes, farmers missed the optimum application time of preemergence herbicides due to onset of erratic rains at that time or due to other reasons. Weed flora in DSR is very complex and a single use of a pre- or post-emergence herbicide does not provide effective weed control in DSR (Mahajan et al., 2009). The use of herbicide combinations, whether the herbicides are applied simultaneously (tank-mixed) or sequentially, generally improves weed control compared with a single herbicide application (Mahajan and Timsina, 2011). Earlier, Mahajan and Chauhan (2013) revealed that sequential applications of pre- and post-emergence herbicides provided better weed control than the sole application of pre- or post-emergence herbicides in DSR. Among the post-emergence herbicides, bispyribac-sodium (bispyribac hereafter), azimsulfuron, and fenoxaprop-p-ethyl (fenoxaprop, hereafter) are widely used by the farmers in DSR. However, each herbicide provides selective weed control, for instance, bispyribac is effective mainly against Cyperus iria L. and azimsulfuron is effective mainly against Cyperus rotundus L. (Mahajan and Chauhan, 2013). Earlier, fenoxaprop without safener was used in DSR for the control of Leptochloa chinensis (L.) Nees and Dactyloctenium aegyptium (L.) Willd., but it also caused toxicity to the rice crop (Gopal et al., 2010). A new formulation of fenoxaprop (with isoxadifen, a safener), a relatively new herbicide in India, inhibits the synthesis of a majority of fatty acids in the meristem tissues of weeds by acting on ACCase within 1e2 weeks of application without any toxicity to the rice crop, depending on the environmental conditions. Isoxadifen reduces the foliar uptake of fenoxaprop in rice and accelerates its transformation into nonphytotoxic metabolites. According to Blouin et al. (2010), fenoxaprop provides excellent control of major grasses such as L. chinensis, D. aegyptium, Digitaria sanguinalis (L.) Scop., and Echinochloa colona (L.) Link. that are predominant in DSR fields. Because fenoxaprop does not have an activity on broadleaf weeds or sedges, it is likely that other herbicide(s) with an activity on broadleaf or
91
sedge weeds will be needed in a weed control program containing fenoxaprop in DSR. It would be beneficial in DSR to apply fenoxaprop plus another herbicide with broadleaf or sedge activity in a mixture, saving both time and cost. However, often broadleaf or sedge herbicides in a mixture with herbicides with grass activity, such as fenoxaprop, may antagonise or reduce the activity of the herbicide on grass weeds. Thus, the identification of compatibility of potential tank-mix herbicides with fenoxaprop is important in DSR. Such information will help DSR farmers to achieve broad spectrum of weed control. Research surveys at the farmers' fields revealed that control of complex weed flora with a single post-emergence herbicide application is really a difficult task for the DSR farmers (Mahajan et al., 2013, 2009). Undoubtedly, the development and availability of effective post-emergence herbicides have encouraged farmers to try this new method of crop establishment (DSR) in Asia. As a result, the area under DSR in the north-western part of the Indo-Gangetic Plains is increasing (Mahajan et al., 2013). However, the emergence of new and complex weed flora in DSR restricts the area expansion and sustainability of this crop establishment method. Literature suggests that the repeated use of the same herbicides encourages the problem of herbicide resistance in weeds (Kim, 1996). For a broad spectrum of weed control in DSR, applications of herbicides with different modes of action (chemistry) is needed. Applications of different herbicides as a tank mixture may prove helpful in delaying the problem of herbicide resistance as well as a shift in weed flora, which is invariably associated with the use of a single herbicide (Wrubel and Gressel, 1994). Diggle et al. (2003) in a specific modelling study revealed that; where the assumption of independent resistance are met, resistance to the mixture can only arise via the spontaneous evolution of resistance mechanisms to both (or all) mixture components. The likelihood of this mechanism decreases with each additional herbicide in the mixture (Wrubel and Gressel, 1994). Therefore, the combined application of different herbicides with different modes of action is required for broad spectrum weed control in DSR and for delaying the development of herbicide resistance. To the best of our knowledge, a very few studies in this line have been conducted in DSR grown in this region. Thus, it is essential to identify economic and effective herbicide combinations for managing complex weed flora in DSR. This study was conducted for generating detailed information for managing a mixed population of grass, sedge, and broadleaf weeds in DSR effectively and economically with tank mix applications of newly available postemergence herbicides. 2. Materials and methods 2.1. Experimental site A field study was conducted for two years (wet seasons of 2013 and 2014) at the research farm of Punjab Agricultural University, Ludhiana (30.93 N, 75.86 E), India. The climate is semiarid, with an average annual rainfall of 400e700 mm (75e80% of which is received from July to September), a minimum temperature of 0e4 C in January, and a maximum temperature of 41e45 C in June. The soil type at the experimental site was Fatehpur Series sandy loam (Entisol, Typic Ustipsament) with 0.3% organic matter with a pH of 7.2. Groundwater depth at the site was below 25 m, and the water was non-saline. 2.2. Experimental design and treatments The treatments in each year were arranged in a randomised complete block design with three replications. Twelve weed control
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treatments were included to evaluate different herbicide options for weed control in DSR (Table 1). Herbicides included in the study were pendimethalin (Stomp, BASF India Ltd.), bispyribac-sodium (Nominee gold, PI Industries), azimsulfuron (Segment, Dupont India Ltd.), and fenoxaprop (Rice star, Bayer, India).
are reported with interpretation based on transformed data. Relationships between grain yield and weed biomass were assessed using linear regression analysis (Sigma Plot 10.0). Since, every penny has a value for farmers; no statistical analysis was done for additional net return in response to herbicide use.
2.3. Experimental details and measurements
3. Results and discussion
In each year, rice (cv. PR-115, a cultivar with duration of 120 d) was seeded in the last week of June and harvested in October. Fields were prepared by cultivating twice with a disc harrow, followed by levelling with a wooden board. Seeds were sown with a single-row drill at a seeding rate of 25 kg ha1 at 20-cm row spacing. The size of the plots was 5.5 m by 2.0 m. The field was surface irrigated immediately after sowing, so that it may have enough moisture at the time of pendimethalin (pre-emergence herbicide) application. Nitrogen (150 kg ha1) was applied in four equal splits at 15, 30, 45, and 60 d after sowing (DAS). Recommended rates of chlorpyriphos (500 g ai ha1, Chlorguard, Gharda Chemical Ltd.) and propiconazole (62.5 g ai ha1, Tilt, Syngenta India Ltd.) were used to control insects and diseases. Pre-emergence (PRE) herbicides were applied at 3 DAS and post-emergence (POST) herbicides were applied at 25 DAS. Herbicides were applied with the use of a knapsack sprayer fitted with a flat-fan nozzle and water as a carrier at 500 L ha1 for pre-emergence spray and at 375 L ha1 for post-emergence spray. Species-wise density and total biomass of weeds were measured at maturity. Weed density was recorded in two quadrats (0.5 m by 0.4 m) placed randomly in each plot. Weeds were cut at ground level, washed with tap water, sun-dried, oven-dried at 70 C for 48 h, and then weighed. Grain yield was measured form an area of 7.2 m2 in the centre of each plot and expressed in t ha1 at14% moisture. Weed control efficiency (WCE, %) was calculated using the formula
3.1. Weed density and biomass
WCE ¼ ðweed biomass in non treated plot weed biomass in treated plotÞ= ðweed biomass in non treated plotÞ 100
2.4. Statistical analyses Data generated from the experiments were analysed using GenStat V.10 and mean comparisons were performed based on the least significant difference (LSD) test at 0.05 probability. Weed density data were transformed using square-root transformation [√(xþ1)] before analyses. The non-transformed weed density data
Table 1 Herbicide treatments used in the study. Herbicide treatments
Dose (g a.i. ha1)
Application time (days after sowing)
Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuronplusbispyribac Bispyribacplusfenoxaprop Azimsulfuronplusfenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop
e 750 25 20 67.5 15plus 18.7 18.7 plus50.6 15plus50.6 750 fb 25 750 fb 67.5 750 fb 20 15plus 18.7plus 50.6
e 3 20 20 20 20 20 3 fb 3 fb 3 fb 3 fb 20
Abbreviations: fb ¼ followed by.
20 20 20 20
The experimental plots contained C. iria, C. rotundus, D. aegyptium, D. sanguinalis, L. chinensis, Echinochloa colona, Eleusine indica, Digera arvensis, Ludwigia octovalvis, Panicum brevifolium, Euphorbia spp., Eragrostis pilosa, etc. However, species-wise results are presented for the first six weeds only, as they were dominant in the samples. 3.1.1. C. iria and C. rotundus The data for C. iria and C. rotundus were combined as our emphasis was more on Cyperus spp. rather than on individual species. The tank mix application of azimsulfuron plus bispyribac plus fenoxaprop significantly reduced the density of sedges (C. iria and C. rotundus) compared with the non-treated control (Table 2). Sedge densities in the plots treated with pendimethalin, bispyribac, and fenoxaprop individually were 32, 5, and 29 plants m2 in 2013 and 21, 11, and 23 plants m2 in 2014 compared with 36 and 28 plants m2 in the non-treated plots in 2013 and 2014, respectively. No sedge plants were observed in the plots treated with the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop, azimsulfuron alone, and pendimethalin fb bispyribac or azimsulfuron. The application of pendimethalin and fenoxaprop sole, and pendimethalin fb fenoxprop provided similar density of sedges as in the non-treated plots. Sedge density with tank mix application of azimsulfuron plus bispyribac, bispyribac plus fenoxaprop, and azimsulfuron plus fenoxaprop was similar to that with the application of bispyribac (5 plants m2 in 2013 and 11 plants m2 in 2014). Pendimethalin and fenoxaprop were ineffective against sedges. However, the application of bispyribac and azimsulfuron controlled sedges effectively when applied alone or tank mixed. The superiority of azimsulfuron compared to bispyribac against sedges was due to the combined occurrence of C. rotundus and C. iria in the field. Mahajan and Chauhan (2013) revealed that azimsulfuron was more effective against C. rotundus as compared to bispyribac. In the present studies, the application of azimsulfuron provided complete control of sedges (C. rotundus and C. iria). The results also suggested a poor control of the two sedges by fenoxaprop. Tank mix application of azimsulfuron plus bispyribac did not provide 100% control of sedges as with sole application of azimsulfuron in 2014. This might be due to some degree of antagonistic effect that provided relatively lower control of C. rotundus as compared to azimsulfuron. It is quite possible that antagonistic effect of these herbicides varied with the weather condition, as tank mix application of azimsulfuron plus bispyribac and sole application of azimsulfuron provided similar control of sedges during the first year of study. 3.1.2. D. aegyptium The lowest density of D. aegyptium (Table 2) was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (1.3 plants m2 in 2013 and 0 plants m2 in 2014). D. aegyptium density observed following the application of pendimethalin was 13 and 8 plants m2 compared with 33 and 28 plants m2 in the non-treated control in 2013 and 2014, respectively. In both years, the application of bispyribac, azimsufuron, and tank mixture of azimsulfuron plus bispyribac resulted in similar
(143) (51) (70) (61) (57) (67) (30) (32) (14) (33) (19) (3) Abbreviations: fb ¼ followed by.
2014
11.9 7.21 8.40 7.88 7.60 8.21 5.39 5.70 3.83 5.71 4.42 1.67 1.77 (174) (74) (79) (60) (65) (73) (34) (37) (29) (53) (23) (5) 13.1 8.65 8.86 7.74 8.09 8.60 5.70 6.09 5.51 7.29 4.72 2.33 2.07
2013 2014
5.82 (33) 2.33 (5) 1.41 (1) 1.82 (3) 3.40 (11) 1.41 (1) 2.61 (8) 2.53 (7) 1 (0) 2.61 (8) 30 (8) 1.67 (3) 1.53 3.98 (15) 1.71 (2) 3.60 (12) 3.60 (12) 1.27 (1) 3.60 (12) 1.28 (10) 1.13 (0) 1.62 (2) 1 (0) 1.27 (1) 1 (0) 0.39
6.35 3.20 2.49 1.41 4.10 2.53 3.11 3.32 2.49 3.13 3.40 2.08 1.72
(40) (9) (5) (1) (16) (7) (9) (11) (5) (12) (11) (4)
2013 2013
4.02 (15) 1.71 (2) 3.69 (13) 3.60 (12) 1.14 (0) 3.69 (13) 1.13 (0) 1.13 (0) 1.52 (1) 1 (0) 1.14 (0) 1 (0) 0.43
2014
4.10 (16) 3.0 (8) 1.82 (3) 1.82 (3) 2.08 (4) 1.82 (3) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 0.83 4.41 (19) 2.74 (7) 2.08 (4) 2.08 (4) 2.08 (4) 1.82 (3) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1.01
2013 2014
4.66 (23) 2.53 (7) 4.71 (22) 4.88 (24) 3.60 (12) 5.01 (25) 2.04 (5) 2.94 (8) 1 (0) 1.41 (1) 2.53 (7) 1 (0) 1.89 5.26 (29) 3.32 (11) 5.12 (27) 4.53 (23) 3.20 (9) 4.57 (21) 3.06 (11) 2.93 (8) 2.24 (4) 2.49 (5) 2.53 (7) 1 (0) 1.98
2013 2014
5.25 (28) 2.73 (8) 4.68 (22) 4.53 (20) 2.82 (7) 4.78 (23) 3.20 (9) 3.58 (12) 3.60 (12) 1.82 (3) 2.08 (4) 1 (0) 1.54 (33) (13) (25) (20) (6) (27) (9) (13) (19) (5) (5) (1.33) 5.73 3.64 5.03 4.49 2.54 5.24 3.12 3.64 4.42 2.49 2.28 1.41 1.69
2013 2014
3.1.3. D. sanguinalis D. sanguinalis density in the non-treated control was 29 and 23 plants m2 in 2013 and 2014, respectively (Table 2). In both years, the lowest density of D. sanguinalis was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (~0 plants m2) and it was similar to the density in all the sequential herbicide treatments tested [i.e., pendimethalin fb bispyribac, pendimethalin fb azimsulfuron, and pendimethalin fb fenoxaprop]. The application of bispyribac, azimsulfuron, and tank mix of azimsulfron plus bispyribac provided density of D. sanguinalis similar to that in non-treated control. The application of fenoxaprop reduced the density of D. sanguinalis (9 and 12 plants m2 respectively in 2013 and 2014) as compared to then on-treated control (29 and 23 plants m2 in 2013 and 2014). The D. sanguinalis density in the pendimethalin-treated plots was 11 and 7 plants m2 in 2013 and 2014, respectively. Our results revealed that the sequential application of pendimethalin fb fenoxaprop reduced the density of D. sanguinalis by 83 and 96% during 2013 and 2014, respectively. However, a complete control (~100%) was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop due to vigorous growth of crop that did not allow later flush of D. sanguinalis. In a recent study, bispyribac provided poor control (30e40%) of D. ciliaris (Chauhan and Abugho, 2012). Similarly in another study, Mahajan and Chauhan (2013) revealed that azimsufuron was not effective in controlling D. sanguinalis.
5.36 (28) 4.71 (21) 3.40 (11) 1 (0) 4.78 (23) 2.33 (5) 2.74 (7) 2.28 (5) 1 (0) 4.66 (21) 1 (0) 1 (0) 1.17
2013
93
D. aegyptium density as observed in the non-treated control. The application of fenoxaprop (6 plants m2 in 2013 and 7 plants m2 in 2014), tank mix of bispyribac plus fenoxaprop (9 plants m2 each in 2013 and 2014), and azimsulfuron plus fenoxaprop (13plants m2 in 2013 and 12 plants m2 in 2014) resulted in similar D. aegyptium density; however, these densities were lower than those in the non-treated control. D. aegyptium density following the tank mix application of azimsulfuron plus fenoxaprop and bispyribac plus fenoxaprop was higher than that following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop, mainly because of the appearance of late emerging seedlings of D. aegyptium. The rice crop following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop was almost weed-free and did not allow the later flush of weed seedlings to grow due to vigorous growth of the crop. Mahajan and Chauhan (2013) in an earlier study revealed that the single application of azimsulfuron and bispyribac did not control D. aegyptium.The sequential application of pendimethalin fb azimsulfuron proved superior in controlling D. aegyptium. Because, this treatment was quite effective against C. rotundus, thus helped the crop in attaining vigorous growth at the initial stage of the crop that in turn provided smothering effect on D. aegyptium.
6.07 (36) 5.69 (32) 2.49 (5) 1 (0) 5.46 (29) 1.41 (1.33) 2.24 (4) 2.0 (5) 1 (0) 5.60 (31) 1 (0) 1 (0) 1.22 Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuron plus bispyribac Bispyribac plus fenoxaprop Azimsulfuron plus fenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop LSD (0.05)
2014
Other weeds Leptochloa chinensis Echinochloa colona Digitaria sanguinalis Dactyloctenium aegyptium Cyperus spp.
Weed count (no.m2) Herbicide treatments
Table 2 Effect of treatments on weed density (number m2) at maturity. Square-root transformed [ ¼ √(xþ1)] values were used for analyses and original weed density values are shown in parentheses.
Total weed count
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3.1.4. E. colona The density of E. colona in the non-treated control was 19 and 16 plants m2 during 2013 and 2014, respectively (Table 2). All the tested herbicide treatments reduced the density of E. colona as compared to the non-treated control. The lowest density of E. colona (0 plant m2) was observed following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop and it was similar to all the other sequential and tank mix herbicide treatments. The application of azimsulfuron, bispyribac, and fenoxaprop provided similar density of E. colona and proved effective in reducing its density compared with the non-treated control. Our findings showed that almost all the tested herbicides were effective for the control of E. colona; however, the control was better when herbicides were applied as a tank mix or
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in sequential applications (pre-emergence fb post-emergence). This study also revealed that relatively pendimethalin and fenoxaprop-prop were less effective against E. colona as compared to bispyribac and azimsulfuron. 3.1.5. L. chinensis The density of L. chinensis in the non-treated control was 15 plants m2 during both the years (Table 2). Bispyribac, azimsulfuron, and the tank mixture of azimsulfuron plus bispyribac had L. chinensis density similar to the non-treated control. All the other herbicide combinations proved effective in controlling this weed. An earlier study revealed that bispyribac and azimsulfuron were ineffective against L. chinensis (Mahajan and Chauhan, 2013). 3.1.6. Other weeds The density of other weeds in the non-treated control plot was 40 and 33 plants m2 in 2013 and 2014, respectively (Table 2). All herbicide treatments reduced the density of other weeds significantly as compared to the non-treated control. Density of other weeds following the application of fenoxaprop was 16 and 11 plants m2 in 2013 and 2014, respectively, and it was higher than in the azimsulfuron-treated plots (1 and 3 plant m2 in 2013 and 2014, respectively).
with the sequential applications of pendimethalin fb fenoxaprop (64.3e67.2 g m2) and pendimethalin fb bispyribac (62.5e74.4 g m2). Total weed biomass in the tank mix applications of azimsulfuron plus fenoxaprop (76.7 g m2 in 2013 and 98 g m2 in 2014) and bispyribac plus fenoxaprop (151.8 g m2 in 2013 and 164.3 g m2 in 2014) was similar during 2013 and 2014. The tank mixture of azimsulfuron plus fenoxaprop showed superiority for weed control as compared to the single application of bispyribac and azimsulfuron. These results suggest that tank mixing of azimsulfuron plus fenoxaprop might have greater synergistic effect for broad spectrum weed control as total weed biomass was lower than that in the plots treated with single applications of herbicides. The effect was more pronounced when this combination was again mixed with bispyribac and provided excellent broad spectrum weed control. Blouin et al. (2010) found that mixtures of ALSinhibitor herbicides with fenoxaprop, if applied in optimum doses, enabled greater weed control in rice. Similarly in another study, Leon et al. (2002) revealed that Ricestar (fenoxaprop-P-ethyl plus safener) tank-mixed with Arrosolo (propanil plus molinate) applied at mid post-emergence (35 days after sowing) controlled E. colona, Leptochloa panicoides (Presl) Hitchc., and broadleaf Brachiaria platyphylla (Griseb.) Nash by 88e95%. 3.2. Grain yield response
3.1.7. Total weed density Total weed density in the non-treated control plot was 174 and 133 plants m2 in 2013 and 2014, respectively (Table 2). All herbicide treatments reduced the total weed density significantly as compared to the non-treated control. The lowest total weed density was observed after the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (5 plants m2 in 2013 and 3 plants m2in 2014). Total weed density following the single application of pendimethalin was 74 and 51 plants m2 in 2013 and 2014, respectively, and it was similar to that for the tank mix of azimsulfuron plus bispyribac (73 plants m2 in 2013 and 67 plants m2 in 2014). Total weed density following the tank mix application of herbicides was lower than pendimethalin alone. Total weed density following the single application of azimsulfuron, bispyribac, and fenoxaprop was similar to the density in the pendimethalin-treated plots. Among the sequential herbicide treatments, total weed density in the plots treated with pendimethalin fb bispyribac and pendimethalin fb azimsulfuron was similar in both years; however, lower than non-treated control. 3.1.8. Total weed biomass Total weed biomass in the non-treated control was 421.7 and 410.3 g m2 in 2013 and 2014, respectively (Table 3). All herbicide treatments significantly reduced weed biomass compared to the non-treated control in both years, except pendimethalin in 2013 (Table 4). Weed control efficiency with single herbicide applications ranged from 19 to 53% in 2013 and 27e59% in 2014; with tank mixture of two herbicides ranged from 35 to 82% in 2013 and 54e76% in 2014; with sequential spray varied from 73 to 85% in 2013 and 27e59% in 2014. Weed biomass following a single application of bispyribac, fenoxaprop, and azimsulfuron was similar. Compared with the non-treated control, the sole application of these three herbicides, respectively, reduced weed biomass by 53.4, 52.9, and 53.2% in 2013, and 55.2, 54.4, and 58.9% in 2014. In both years, these treatments also reduced total weed biomass greater than that after pendimethalin application. The lowest weed biomass (8.5 and 5.6 g m2 in 2013 and 2014, respectively) and highest weed control efficiency (~98%) was observed in the plots treated with tank mix application of azimsulfuron plus bispyribac plus fenoxaprop. Biomass in these plots, however, was similar to the biomass produced in the plots treated
Rice grain yield following all herbicide treatments ranged from 2.96 e 7.23 t ha1and 3.46 e 7.86 t ha1, while the non-treated plots yielded 1.92 and 2.67 t ha1 in 2013 and 2014, respectively (Table 3). The highest grain yield was recorded in the plots treated with the tank mix of azimsulfuron plus bispyribac plus fenoxaprop (7.23 t ha1 in 2013 and 7.86 t ha1in 2014) and it was similar to the yield observed in the plots treated with the tank mix of azimsulfuron plus fenoxaprop, pendimethalin fb bispyribac, pendimethalin fb fenoxaprop, and pendimethain fb azimsulfuron. In both years, grain yield in the plots treated with azimsulfuron (4.49 t ha1in 2013 and 5.38 t ha1 in 2014), bispyribac (4.67 t ha1 in 2013 and 5.31 t ha1 in 2014), and fenoxaprop (5.21 t ha1 in 2013 and 6.10 t ha1 in 2014) was similar, but greater than the grain yield recorded in the pendimethalin-treated plots. Plots treated with the single herbicide (azimsulfuron, bispyribac, or fenoxaprop) had lower grain yield compared to all the sequential spray treatments and tank mixed applications of azimsulfuron plus fenoxaprop and azimsulfuron plus bispyribac plus fenoxaprop. Grain yield in the plots treated with azimsulfuron plus bispyribac, bispyribac alone, and azimsulfuron alone were similar. Among herbicide treatments, the lowest grain yield was observed in the plots treated with pendimethalin, owing to a high weed pressure experienced by the crop. As expected, the correlation of weed biomass and grain yield was negative in the present study. Weed biomass accounted for 96% and 93% variation in grain yield during 2013 and 2014, respectively (Fig. 1). It was observed that weeds, namely E. colona, L. chinensis, D. sanguinalis, and D. aegyptium appeared in the field in several flushes. Although total weed density decreased from 174 to 74 plants m2 and 143 to 51 plants m2 after the pendimethalin application as compared to the non-treated control in 2013 and 2014, respectively, weed biomass was merely reduced by19%in 2013 and 27% in 2014 after this herbicide treatment. These results indicate that weeds posed high competition to the crop for water, nutrient, and light, causing poor crop growth and resulted in lower grain yield in the pendimethalin-treated plots compared to other herbicide treatments. Grain yield in the single herbicide-treated plots was similar because of similar weed pressure, in terms of weed biomass faced by the crop. Weed density data revealed that azimsulfuron and
G. Mahajan, B.S. Chauhan / Crop Protection 72 (2015) 90e96
95
Table 3 Effect of herbicide treatments on paddy grain yield (t ha1) and weed biomass (g m2) at maturity. Herbicide treatments
Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuron plus bispyribac Bispyribac plus fenoxaprop Azimsulfuron plus fenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop LSD (0.05)
Total weed dry matter (g m2)
Weed control efficiency (%)
Grain yield (t ha1)
2013
2014
2013
2014
2013
2014
421.7 341.3 196.3 198.3 197.3 272.7 151.8 76.7 74.4 64.3 115.2 8.5
410.3 300.3 183.5 187.0 168.3 190.0 164.3 98.0 62.5 67.2 110.0 5.67
e 19.1 53.4 53.0 53.2 35.3 64.0 81.8 82.3 84.7 72.7 98
e 26.8 55.3 54.4 59.0 53.7 60.0 76.1 84.8 83.6 73.2 98.6
1.92 2.96 4.67 4.49 5.21 4.58 5.36 6.56 6.79 6.85 6.57 7.23
2.67 3.46 5.31 5.38 6.10 4.88 6.49 7.32 7.24 7.46 7.24 7.86
100.4
79.6
e
e
0.7
0.8
Abbreviations: fb ¼ followed by.
bispyribac were quite effective in controlling sedges. A single application of fenoxaprop failed to control sedges; however, it caused a drastic reduction in the density of L. chinensis, D. aegyptium, and D. sanguinalis. Therefore, overall total weed density and biomass remained similar with the application of a single herbicide, resulting in similar grain yield. Among the tank mix herbicide treatments, azimsulfuron plus bispyribac provided lower yield due to poor control of L. chinensis, D. aegyptium, and D. sanguinalis. Average of the two-year mean data showed that total weed biomass reduced by 32, 62, and 97% when fenoxaprop was tank mixed with bispyribac, azimsulfuron, and both azimsulfuron plus bispyribac, respectively, as compared to the tank mix application of azimsulfuron plus bispyribac. It means L. chinensis, D. aegyptium, and D. sanguinalis offered great competition to the crop and their control with fenoxaprop helped in increasing the yield. All sequential herbicide treatments resulted in similar yield because of similar weed biomass observed in each plot. The highest grain yield following the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop was due to the lowest weed biomass observed in the crop. The synergistic effect of these herbicides in tank mixing provided excellent weed control. It was observed that the rice crop faced weed competition before the spray of the tank
mixture of azimsulfuron plus bispyribac plus fenoxaprop. However, after the spray of this tank mixture, crop grew vigorously and did not allow the later flushes of weeds to grow, resulting in the highest yield. Therefore, the present study showed that the azimsulfuron plus bispyribac plus fenoxaprop treatment resulted in an additive response for weed control. Christopher et al. (2005) also reported that fenoxaprop plus bentazon or propanil plus molinate resulted in an additive response for E. colona control. This study revealed that when ACCase inhibitor herbicides are used at substantially lower than labelled rates in combination with ALS inhibitors, the activity of the combination is superior to the components when used alone. Furthermore, there are no antagonistic effects, in fact, the effect is synergistic. This synergistic effect will broaden the options for economic weed control for DSR farmers by allowing for a wider application window (greater flexibility in timing of application) and broader spectrum of weed control, such as control of hardy grass weeds (L. chinensis, D. aegyptium, and D. sanguinalis); not normally controlled by bispyribac and azimsulfuron. 3.3. Economics Additional costs due to herbicide treatments varied from 24.6 to 60.4 USD ha1; lowest with pendimethalin and highest with the
Table 4 Additional cost and net profit ($) occurred in response to herbicide use. Herbicide treatments
Non-treated control Pendimethalin Bispyribac Azimsulfuron Fenoxaprop Azimsulfuron plus bispyribac Bispyribac plus fenoxaprop Azimsulfuron plus fenoxaprop Pendimethalin fb bispyribac Pendimethalin fb fenoxaprop Pendimethalin fb azimsulfuron Azimsulfuron plus bispyribac plus fenoxaprop
Additional cost of herbicide (USD ha1)
24.6 27.1 28.5 25 41.7 39.0 40.2 53.1 49.6 53.1 60.4
Additional income with herbicide use (USD ha1)
Additional net profit with herbicide use (USD ha1)
2013
2014
2013
2014
242.7 641.7 599.7 767.7 620. 802.7 1082.7 1136.3 1150.3 1061.7 1239
184.3 616 632.3 800.3 515.7 891.3 1085 1066.3 1117.7 1066.3 1211
218.1 614.6 571.1 742.7 579.0 763.6 1042.5 1083.2 1100.7 1008.5 1178.5
159.7 588.9 603.8 775.3 473.9 852.3 1044.8 1013.2 1068.1 1013.2 1150.5
Abbreviations: fb ¼ followed by. Price of paddy 233.3 USD t1; Cost of herbicides (Pendimethalin- 9.83 USD litre1; Azimsulfuron 71.3 USD 100 g1; Bispyribac 108.3 USD litre1; fenoxaprop e 25 USD litre1); 1 USD (US dollar) ¼ 60 Indian Rupees.
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plots treated with the tank mixture of azimsulfuron plus bispyribac plus fenoxaprop recorded highest yield because of lowest weed biomass in these plots. Our study thus demonstrated that the sequential applications of pre- and post-emergence herbicides are needed for maintaining good weed control and yield in DSR. Somehow, if farmers missed the application of pre-emergence herbicides (e.g., pendimethalin) due to erratic rains or other reasons, effective weed control and high yield can still be obtained with the tank mix application of azimsulfuron plus fenoxaprop or azimsulfuron plus bispyribac plus fenoxaprop. Tank mix application of azimsulfuron plus bispyribac plus fenoxaprop provided complete control of sedges especially C. iria and C. rotundus, grass and broadleaf weeds with weed control efficiency ~98%.Among the herbicide treatments, the profitability was highest after the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop. Thus, a synergistic composition of azimsulfuron plus bispyribac plus fenoxaprop, when applied to DSR, allows a reduction in the amount of herbicide needed, greater flexibility in timing of the application besides offering broad spectrum weed control.
References
Fig. 1. Relationship between weed biomass (g m2) and grain yield (t ha1) during 2013 (a) and 2014 (b).
tank mix application of azimsulfuron plus bispyribac plus fenoxaprop (Table 4). With the single herbicide application, the cost varied from 24.6 to 28.5 USD ha1 and it was highest for azimsulfuron. The herbicide cost with the tank mix application of two herbicides ranged from 39.0 to 41.7 USD ha1. In sequential herbicide treatments, herbicide cost varied from 49.6 to 53.1 USD ha1. Additional net profit (1179 and 1151 USD ha1 in 2013 and 2014, respectively) was highest with the tank mix application of azimsulfuron plus bispyribac plus fenoxaprop. The application of pendimethalin provided additional net profit, amounting to 218 and 160 USD ha1 in 2013 and 2014, respectively. With the application of single herbicide, additional profit due to herbicide use varied from 571 e 743 and 589- 775 USD ha1 in 2013 and 2014, respectively; highest with fenoxaprop. Among the tank mixed herbicide treatments, additional profit of greater than 1000 USD ha1 was observed with azimsulfuron plus fenoxaprop (1043 USD ha1 in 2013 and 1045 USD ha1 in 2014) and azimsulfuron plus bispyribac plus fenoxaprop (1179 USD ha1 in 2013 and 1151USD ha1 in 2014). Additional net profit with the tank mix application of azimsulfuron plus bispyribac was lower than the single application of herbicides in both years. With the sequential herbicide treatments, additional profit due to herbicide use varied from 1009 to 1101 USD ha1 and 1013e1068 USD ha1 in 2013 and 2014, respectively. 4. Conclusions A single application of herbicide (pre- or post-emergence) did not control the complex weed flora in DSR. Weed biomass and grain yield significantly improved when fenoxaprop was tank mixed with azimsulfuron. The sequential application of pendimethalin fb azimsulfuron, bispyribac, or fenoxaprop provided better weed control than the single application of any of these herbicides. The
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