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Efficacy and phytotoxicity of different rates of oxadiargyl and pendimethalin in dry-seeded rice (Oryza sativa L.) in Bangladesh
Crop Protection 72 (2015) 169e174
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Crop Protection journal homepage: www.elsevier.com/locate/cropro
Efficacy and phytotoxicity of different rates of oxadiargyl and pendimethalin in dry-seeded rice (Oryza sativa L.) in Bangladesh Sharif Ahmed a, *, Bhagirath Singh Chauhan b a b
~ os, Philippines International Rice Research Institute, Los Ban 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 27 January 2015 Received in revised form 22 March 2015 Accepted 23 March 2015 Available online 27 March 2015
A field study was established to evaluate oxadiargyl and pendimethalin during the wet seasons in Bangladesh in 2012 and 2013. The study evaluated the following treatments: oxadiargyl applied at 80, 120, and 160 g ai ha1; pendimethalin at 800, 1200, and 1600 g ai ha1; partial weedy; and weed-free. Rice plant density was greatly affected by weed control treatment. Lower density and lower uniformity of the rice plant stand occurred as a result of increased rates of herbicides. Increased rates of pendimethalin were more toxic than increased rates of oxadiargyl. Both herbicides effectively controlled Digitaria ciliaris, Echinochloa colona, and Phyllanthus niruri; however, they were unable to control Murdannia nudiflora. Oxadiargyl controlled Cyperus rotundus across rates by 31e55%, but pendimethalin was completely ineffective on it, and higher rates of both herbicides had no effect in controlling this weed. Both herbicides at higher rates reduced total weed biomass significantly. Among herbicide treatments, the highest yield (3.7e4.0 t ha1) was recorded in plots treated with oxadiargyl at 160 g ai ha1 and the lowest yield (2.4e2.8 t ha1) was in plots treated with pendimethalin at 1600 g ai ha1. Results from our study suggest that a higher rate of oxadiargyl can increase yield by suppressing weeds in dry-seeded rice systems. Similar to the results of oxadiargyl, pendimethalin at higher rates also greatly suppressed weeds; however, yield decreased due to phytotoxicity to rice seedlings. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Herbicide rate Plant density Plant injury Weeds density Weed biomass Rice yield
1. Introduction Dry-seeded rice (DSR) is an alternative labor- and water-saving rice production system. Because of farm labor and irrigation water shortage, farmers in some Asian countries are becoming interested in dry-seeded rice systems (Ahmed and Chauhan, 2014; Kato and Katsura, 2014; Mahajan et al., 2013). This system of rice establishment is conducive to mechanization and there is no need for puddling (land preparation in standing water) and transplanting which are needed for conventional transplanted rice systems. In addition to saving labor and water, dry-seeded rice improves the soil physical and chemical properties, which facilitate the growth and yield of non-rice crops grown in rotation with rice (Gathala et al., 2011; Singh et al., 2014). Despite the multiple benefits of dry-seeded rice, weed management is a major challenge to the success of these systems (Chauhan and Johnson, 2011a; Rao et al., 2007). Weeds are
* Corresponding author. E-mail address: [email protected] (S. Ahmed). http://dx.doi.org/10.1016/j.cropro.2015.03.021 0261-2194/© 2015 Elsevier Ltd. All rights reserved.
comparatively greater in number in this system than in traditional transplanted rice, because of the simultaneous emergence of rice and weeds and the absence of standing water at this stage (Chauhan, 2012; Rao et al., 2007). Inherently, weeds are more competitive in nutrients and they grow faster than the crop (Blackshaw et al., 2003). If weeds are not controlled in dry-seeded systems, yield loss can be greater than 90% (Chauhan and Johnson, 2011b). Yield loss in dry-seeded systems depends on weed infestation level and varies from country to country; for example, yield loss is up to 93% in Nepal (Ranjit, 2007), more than 80% in Pakistan (Khaliq et al., 2012), more than 70% in the Philippines (Chauhan and ~ a, 2012; Phoung et al., 2005), and up to 78% in Bangladesh Open (Ahmed et al., 2014). Therefore, weed management is an important prerequisite in dry-seeded systems. In Bangladesh, weeding by hand is the common practice of controlling weeds; however, this method is becoming impractical because of labor shortage and high labor cost (Ahmed et al., 2011). In addition, hand weeding is difficult at early growth stages, because of the similar morphology of some weeds with rice, such as Echinochloa spp., and Leptochloa chinensis (Ahmed and Chauhan,
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2014; Rahman et al., 2012). Chemical weed control is now available and applications of pre-emergence herbicides offer weed control from the beginning of the crop, facilitating a head start and competitive advantage to the crop (Rahman et al., 2012). Therefore, the use of pre-emergence herbicides is a good option to achieve effective weed control and higher yield in DSR systems (Mahajan and Chauhan, 2013). Herbicides with pre-emergence activity, such as oxadiazon, oxadiargyl, pendimethalin, butachlor, thiobencarb, and oxyfluorfen are available around the world and are commonly used in dry-seeded rice (Chauhan et al., 2012). A recent study in dry-seeded rice found that oxadiargyl and pendimethalin are the most effective pre-emergence herbicides among the available herbicides in Bangladesh (Ahmed and Chauhan, 2014). Oxadiargyl inhibits protoporphyrinogen oxidase, the enzyme that converts protoporphyrinogen IX into protoporphyrin IX, causing rapid membrane peroxidation and cellular death (Dickmann et al., 1997; Lee and Duke, 1994). It works through contact with emerging or recently emerged shoots, but there is slight absorption by the root (Nethra and Jagannath, 2011). Oxadiargyl is commonly used to control annual grasses, sedges, and broadleaf weeds in a range of crops, such as Oryza sativa, Saccharum spontaneum, Helianthus annuus, transplanted vegetables, and perennial crops (Dickmann et al., 1997; EFSA, 2013). Pendimethalin inhibits microtubulin synthesis, which is necessary in the formation of cell walls and in chromosome movement during mitosis (Parka and Soper, 1977). These herbicides are absorbed to a smaller extent by plant root systems and, to a greater extent, by young shoot organs, such as the hypocotyl or coleoptiles (Ashton and Crafts, 1981; Malefyt and Duke, 1984). Pendimethalin is used in the selective control of grass and broadleaf weeds in Zea mays, Glycine max, Allium spp, and Gossypium birsutum (Bhowmick and Ghosh, 2002; Sinha et al., 1996; Tsiropoulos and Miliadis, 1998). Oxadiargyl and pendimethalin are effective pre-emergence herbicides, which are used to control common weeds in dryseeded rice systems. However, the efficacy and phytotoxicity of herbicides with soil activity depend on environmental conditions, application timing, and spray techniques (Jacques and Harvey, 1979; Levene and Owen, 1995). In addition to this, an appropriate herbicide rate is very important in achieving adequate weed control and reducing crop phytotoxicity (Harding et al., 2012). Herbicide rates depend on several factors, including weed seed bank size, presence or absence of residue and soil properties (Blackshaw et al., 2006; Chauhan and Abugho, 2012; Zhang et al., 2000). Previous studies in several crops under different environmental conditions found substantial variations in weed control with different herbicide rates (Zhang et al., 2000). A previous study reported that a high rate of oxadiargyl applied at 150 g ai ha1 caused seedling mortality in rice in anaerobic conditions but not in aerobic conditions (Gitsopoulos and FroudWilliams, 2004). Smith (2004) reported that the application of pendimethalin at rates of 990e1980 g ai ha1 controlled weeds in Basella alba, but the crop was stunted with dark-green color, swollen stem, and sunken mottled leaves. On the contrary, lower pendimethalin rates of 330e660 g ai ha1 were less effective against weeds, and the growth and biomass production of the crop were not affected. In Bangladesh, herbicides used as a pre-emergence in dryseeded systems are based on the recommendations for transplanted rice. In this system, pre-emergence herbicides are applied under moist soil conditions but in transplanted rice systems, they are applied under standing water conditions (Rashid et al., 2012). In addition, Bangladeshi farmers are not concerned about the proper dose of herbicides. Although oxadiargyl and pendimethalin are widely used in dry-seeded rice, information on the effect of different rates of these two herbicides on weeds and rice is limited.
Therefore, this study was established to evaluate the comparative performance of oxadiargyl and pendimethalin at different rates on weed control and crop response in dry-seeded rice systems. 2. Materials and methods A field study was conducted to evaluate the efficacy and phytotoxicity of oxadiargyl and pendimethalin in a dry-seeded system at the Regional Agricultural Research Station in Bangladesh Agricultural Research Institute, Jessore, in the wet (aman) seasons, of 2012 and 2013. The area belongs to agroecological zone number 11, known as the High Ganges River Floodplain. The climate of the area is subtropical, with an average annual rainfall of 1590 mm, minimum temperatures of 6e9 C in January, and maximum temperatures of 36e44 C in AprileMay. The minimum and maximum temperatures and amount of rainfall recorded at the experimental site during the experimental periods are presented in Fig. 1. The soil to a depth of 0e15 cm was clay loam (sand of 31%, silt of 32%, and clay of 37%), with a bulk density of 1.58 g cm3, pH of 7.8, and carbon content of 1%. The study was arranged in a randomised completed block design with three replications. The plot size was 4.5 m 3 m. Eight weed control treatments were included in each season: oxadiargyl applied at 80, 120, and 160 g ai ha1; pendimethalin applied at 800, 1200, and 1600 g ai ha1; partial weedy; and weed-free. Herbicides were applied 2 days after sowing (DAS) using a knapsack sprayer attached with three flat-fan nozzles on a boom, the sprayer delivering 450 L solution ha1. At spraying, the soil was saturated and the next irrigation was applied four days after the spray. Weed-free plots were hand weeded four times at 15, 30, 45, and 70 DAS. In the partial weedy plots, one hand weeding was performed at 40 DAS and weeds were allowed to grow before and after hand weeding. BRRI dhan49 rice was sown at a seeding rate of 40 kg ha1 and a row spacing of 20 cm, using a power tiller operated seed-drill fitted with a fluted-type seed metering device. The crop was sown on June 17 in both years. Fertilizers such as NePeKeSeZn were applied at the rates of 120e15e48e12e2.2 kg ha1 in the form of urea, triple superphosphate (TSP), potassium chloride (KCl),
Fig. 1. Maximum and minimum temperatures and total rainfall (mm) recorded at the experimental site in the aman seasons of 2012 and 2013.
S. Ahmed, B.S. Chauhan / Crop Protection 72 (2015) 169e174
calcium sulphate (gypsum), and zinc sulphate, respectively. Full doses of TSP, MoP, gypsum, and zinc sulphate were applied immediately before sowing. Urea was applied in four equal splits at 14 DAS, at active tillering (30 DAS), at maximum tillering (45 DAS), and at panicle initiation (65 DAS). Immediately after sowing, the field was surface irrigated. After this, irrigation was based on tensiometer readings using a threshold value of 15 kPa at 15-cm soil depth. At each irrigation, a 5 cm flood was established. At 50 DAS, the fungicide tebuconazole plus trifloxystrobin 300 g ai ha1 (Nativo 75 WP, Bayer CropScience Limited, Bangladesh) was applied to control blast, and fipronil 3G 300 g ai ha1 (Regent 3 GR, BASF Bangladesh Limited) was applied at 70 DAS to control stem borers. To evaluate herbicide phytotoxicity in rice, rice plants were counted at 14 DAS from four randomly selected 1-m row lengths in each plot and the reduction (%) in plant stands was calculated by comparing with the non-treated check. The non-uniformity of plant establishment due to herbicide toxicity was determined as the coefficient of variation of means of the 12 rows (4 rows 3 replicates) for each treatment combination. To evaluate the performance of herbicides on individual weed species, weed density and weed biomass were measured at 40 DAS by randomly placing two quadrats, measuring 40 cm by 40 cm, in each plot. Weeds were separated by species, counted, and their biomass was measured after oven drying the samples at 70 C for 72 h. To evaluate the effect of weeds on rice, weed and rice biomass were measured from two 40 cm by 40 cm quadrats at 50% flowering. At harvest, rice panicles were counted from four randomly placed 1-m row lengths in each plot. Rice grain yield was determined from a harvested area of 4.0 m 2.2 m. Grain yield was converted to t ha1 at 14% moisture content. Data were analyzed using analysis of variance (ANOVA) to evaluate differences between treatments, and means were separated using the least significant difference (LSD) at 5% (Crop Stat 7.2; International Rice Research Institute, Philippines). In a combined analysis of data, the interaction between years and treatments was significant; therefore, the data were presented separately for each year. Weed density and biomass data were transformed using square root transformation [√(x þ 0.5)] before analysis. Transformation, did not improve homogeneity. Therefore, the original values were used for analysis and presentation. 3. Results and discussion 3.1. Rice plant density, stands reduction (%), and uniformity Rice plant density was strongly influenced (p < 0.05) by weed control treatments in both years (Table 1). Compared with the non-
Table 1 Effect of weed control treatments on rice plant density (number m2), plant stands reduction (%), and coefficient of variation (%) at 14 d after sowing in the aman seasons of 2012 and 2013. Treatment
Plant density (no. m2)
Plant stands reduction (%)
Coefficient of variation (%)
Herbicide rate (g ai ha1)
2012
2013
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy Weed-free LSD0.05
202 193 184 187 159 128 207 208 8
174 171 156 160 138 115 173 176 11
3 7 12 10 23 39 0 0 9
0 2 11 9 21 34 0 0 7
8.9 10.0 12.3 11.3 14.3 18.1 8.1 6.1 4.8
10.0 10.5 15.7 13.9 16.5 20.4 7.7 8.5 6.5
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treated checks (weed-free and partial weedy), lower plant densities in both years were recorded when rice was treated with pendimethalin at different rates. Rice treated with pendimethalin applied at 800 g ai ha1 had 9e10% lower plant stands, compared with the non-treated (weed-free) check. However, these reductions were 21e23% and 34e39% for the rice treated with pendimethalin at 1200 and 1600 g ai ha1, respectively. In previous studies, Ahmed et al. (2013) and Ahmed and Chauhan (2014) reported the phytotoxicity of pendimethalin in dry-seeded systems. Rice treated with oxadiargyl applied at 80 and 120 g ai ha1 had similar plant density with that of non-treated rice; however, oxadiargyl applied at 160 g ai ha1 reduced plant density significantly. These results were inconsistent with the previous study of Gitsopoulos and Froud-Williams (2004), who reported that oxadiargyl applied at 150 g ai ha1 did not cause mortality in aerobic conditions, but caused crop injury in anaerobic conditions. This study suggests that in dry-seeded systems, pendimethalin can cause phytotoxicity to rice plants when applied at 800 g ai ha1; however, rates higher than this can be more toxic. Because of the phytotoxicity of higher rates of pendimethalin, the uniformity of the crop stand was also affected. Rice plant density had a higher variability when treated with high rates of each herbicide (Table 1). It was observed that higher rates of herbicides did not impair the emergence of rice plants, but toxicity occurred immediately after emergence (visual observations). Common toxicity symptoms for both herbicides included stunting, slower growth, and necrosis on the main culm and leaves of rice. 3.2. Weed density and biomass The common weed species found at the experimental site were Ageratum conyzoides, Cleome rutidosperma, Celosia argentea, Cyperus rotundus, Dactyloctenium aegyptium, Digitaria ciliaris, Echinochloa colona, Eleusine indica, Galinsoga ciliate, Murdannia nudiflora and Phyllanthus niruri. Results were presented only for the top five dominant species because of non-uniform distribution of other weed species. At 40 DAS, the density (Table 2) and biomass (Table 3) of individual weed species, except M. nudiflora were affected by weed control treatments. Oxadiargyl at 80 g ai ha1 reduced C. rotundus density and biomass; however, there was no additional benefit of using higher rates. Compared with the partial weedy rice, oxadiargyl across rates reduced C. rotundus density by 31e55% and biomass by 41e55%. Pendimethalin failed to provide any control of C. rotundus, even at the highest rate. Pendimethalin controlled D. ciliaris better than oxadiargyl. Compared with the partial weedy rice, oxadiargyl was unable to control D. ciliaris density and biomass when applied at 80 g ai ha1; however, the higher rates, 120 and 160 g ai ha1, were able to provide significant control. E. colona was the most dominant weed species in both seasons, and its density was strongly influenced by weed control treatments. Different rates of pendimethalin and oxadiargyl controlled this weed density by more than 80%; however, pendimethalin was more effective than oxadiargyl. E. colona density was reduced by 90e91%, 94e97%, and 99e100% with pendimethalin rates of 800, 1200, and 1600 g ai ha1, respectively, compared with the partial weedy plots. Similarly, oxadiargyl at 80 and 120 g ai ha1 reduced the density of E. colona by 70e76% and 81e83%, respectively. There was no additional benefit to further increase in herbicide dose to 160 g ai ha1. Reduction in biomass followed a trend similar to that for density (Table 3). The density and biomass of P. niruri was reduced by herbicide treatments, and oxadiargyl performed better than pendimethalin (Tables 2 and 3). Compared with the partial weedy plots, across rates, oxadiargyl reduced P. niruri density by 90e100%. On the other hand, pendimethalin reduced P. niruri density by 62e69% when
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Table 2 Effect of weed control treatments on density (number m2) of different weed species at 40 d after sowing in the aman seasons of 2012 and 2013. Treatment
Weed density (no. m2) Cyperus rotundus
Digitaria ciliaris
Echinochloa colona
Murdannia nudiflora
Phyllanthus niruri
Total
Herbicide rate (g ai ha1)
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy LSD 0.05
54 57 51 110 100 123 113 38
128 132 122 189 190 178 192 33
37 19 12 18 7 6 48 12
32 17 15 15 9 0 40 9
45 39 33 17 5 0 194 23
56 38 34 18 11 2 189 12
28 23 26 33 29 34 33 NS
36 37 32 37 43 42 42 NS
5 0 0 22 8 0 58 6
5 0 0 17 8 4 53 7
169 138 122 200 149 163 446 53
257 224 203 276 261 226 516 65
Table 3 Effect of weed control treatments on biomass (g m2) of different weed species at 40 d after sowing in the aman seasons of 2012 and 2013. Treatment
Weed biomass (g m2) Cyperus rotundus
Digitaria ciliaris
Echinochloa colona
Murdannia nudiflora
Phyllanthus niruri
Total
Herbicide rate (g ai ha1)
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy LSD0.05
10 10 8 21 20 20 18 7
18 17 15 27 25 26 32 4
5 3 1 3 1 1 8 4
4 2 2 3 1 0 6 3
14 9 9 3 2 0 44 5
11 7 7 7 4 1 38 4
2 3 2 3 3 4 3 NS
3 4 3 5 5 4 6 NS
1 0 0 4 1 0 9 3
1 0 0 4 1 0 10 1
32 25 20 34 27 25 82 8
37 30 27 46 36 31 92 9
applied at 800 g ai ha1, but it provided 84e100% control at the rates of 1200 and 1600 g ai ha1. Herbicide treatments reduced the density and biomass of total weeds. Compared with the partial weedy treatment, oxadiargyl at different rates reduced weed density by 50e73% (Table 2) and biomass by 60e76% (Table 3). Similar to the results of oxadiargyl, pendimethalin reduced weed density and biomass by 47e66% and 51e70%, respectively. Increased rates of oxadiargyl and pendimethalin did not reduce total weed density; however, they reduced biomass significantly in both years. In dry-seeded rice systems, pre-emergence herbicides are considered the best weed management tool because they provide a head-start to the crop as compared to weeds as the crop emerges in a weed-free environment (Ahmed and Chauhan, 2014; Mahajan et al., 2014; Mahajan and Timsina, 2011; Singh et al., 2006). Pendimethalin and oxadiargyl are widely used in these systems to control grass, broadleaf, and sedge weeds (Gitsopoulos and FroudWilliams, 2004). In this study, oxadiargyl and pendimethalin applied at rates higher than the recommended were more effective against grass weeds, and these results are supported by a previous study (Kirkland et al., 2000). In the previous study, grass weed control was lower when herbicide rates were reduced.
treatment, weed biomass decreased by 27e31% and 12e16%, and rice biomass increased by 6e7% and 2e5% when herbicide dose increased from 80 to 120 or 160 g ai ha1, respectively. Similarly, weed biomass decreased by 33e43% and 21e30% and rice biomass decreased by 11e17% and 37e41% when pendimethalin rates increased from 800 to 1200 or 1600 g ai ha1, respectively.
3.3. Rice and weed biomass at 50% crop flowering
3.4. Rice panicle number
Rice and weed biomass were influenced by herbicide treatment at 50% crop flowering (Table 4). There was a trend of increasing rice biomass with decreasing weed biomass, except for the pendimethalin 1200 and 1600 g ai ha1 treatments. At this stage, the highest weed biomass of 168e182 g m2 and least rice biomass of 296e333 g m2 were found in the partial weedy plots. The lowest weed biomass of 70e81 g m2 was recorded in the pendimethalin 1600 g ai ha1 treatment, which was 58% lower in 2012 and 56% lower in 2013 than the partial weedy treatment. In the oxadiargyl
Rice panicle number was always higher in the season-long weed-free rice and lower in the partial weedy plots (Table 5). All herbicide treatments had a significantly lower panicle number than the weed-free treatment. Between the herbicides, in oxadiargyl treatments, panicle number increased significantly with increase in herbicide rate from 80 to 120 g ai ha1; however, no further increment was observed at 160 g ai ha1. In the pendimethalin treatments, these results were reversed and panicle number decreased with increase in rate. Compared with pendimethalin at
Table 4 Effect of weed control treatments on rice biomass (g m2) and weed biomass (g m2) at 50% crop flowering in the aman seasons of 2012 and 2013. Treatment
Rice biomass (g m2)
Weed biomass (g m2)
Herbicide rate (g ai ha1)
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy Weed-free LSD0.05
575 600 612 558 528 469 333 806 49
542 556 583 523 505 420 296 776 92
123 102 91 125 96 70 168 e 19
137 120 100 143 103 81 182 e 16
S. Ahmed, B.S. Chauhan / Crop Protection 72 (2015) 169e174 Table 5 Effect of weed control treatments on rice panicles (number m2) and rice grain yield (g m2) at harvest in the aman seasons of 2012 and 2013. Treatment
Rice panicles (no. m2)
Rice grain yield (t ha1)
Herbicide rate (g ai ha1)
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy Weed-free LSD0.05
296 328 339 305 292 241 202 381 22
276 308 319 282 270 230 187 352 28
3.4 3.8 4.0 3.5 3.2 2.8 2.1 5.0 0.4
3.1 3.6 3.7 3.2 3.0 2.4 1.8 4.8 0.4
800 g ai ha1, pendimethalin applied at 1200 g ai ha1 did not reduce panicle number but pendimethalin at 1600 g ai ha1 reduced the panicles (18e21%) significantly. 3.5. Rice grain yield Similar to rice panicle number, rice grain yield was also greatly affected by weed control treatment (Table 5). In the herbicidetreated plots, yield was 24e53% higher than in the partial weedy treatment, but 20e48% lower than in the season-long weed-free treatment. In oxadiargyl treatments, yield increased by 14e21% when herbicide rate increased from 80 to 120 or 160 g ai ha1, and this response was observed because higher rates of oxadiargyl controlled weeds better than the lower rate. Pendimethalin rates higher than the recommended rate (e.g., 800 g ai ha1) were more effective against weeds, but this caused a decrease in yield. This was due to crop toxicity at higher rates, resulting in hampered uniformity of the plant population. Singh et al. (2006) similarly reported that increased triclopyr rate from 1000 to 1500 g ha1 was better in reducing weed density and biomass; however, due to phytotoxicity in rice, it resulted in a reduced yield. Oxadiargyl rate, increased from 80 to 120 g ai ha1, was not toxic to rice, and it effectively controlled weeds as well as produced higher yield. The application of pre-emergence herbicides is the best weed management component considered in dry-seeded systems (Mahajan et al., 2014). However, the weed control efficiency of preemergence herbicides depends on proper herbicide doses, application timing, soil water content, and the extent of the weed seed bank (Chauhan, 2012). The results of this study suggest that the pre-emergence herbicide oxadiargyl at a higher rate than the recommended (80 g ai ha1) controlled weeds more effectively and resulted in a higher crop yield. Pendimethalin rates higher than the recommended rate (800 g ai ha1) effectively controlled weeds but resulted in lower crop yield due to phytotoxicity. In this study, we used oxadiargyl and pendimethalin at recommended and higher rates. The objective was to assess the benefits and risks of higher rates of pre-emergence herbicides, which might be helpful in cautioning and making recommendations for farmers who grow dry-seeded rice. However, in this study, we did not use any rate of herbicides lower than the recommended rate, and did not consider cost-effectiveness. But, for farmers, cost-effectiveness is very important. Therefore, further research is needed to evaluate the economics of pre-emergence herbicides at different rates in different soil and environmental conditions. Acknowledgments ~ as for providing We would like to thank Ms. Priscilla Grace Can comments on the manuscript. We also gratefully acknowledge the
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support of the International Fund for Agricultural Development (IFAD); the Cereal Systems Initiative for South Asia (CSISABangladesh); and the Bangladesh Agricultural Research Institute (BARI), Regional Agricultural Research Station at (RARS) Jessore. We especially thank A.K.M. Ferdous of the CSISA-Jessore Hub for his continuous support, and research assistants Alamin, Anwara, and Rima. We also thank all permanent technicians for their admirable technical support.
References Ahmed, S., Chauhan, B.S., 2014. Performance of different herbicides in dry-seeded rice in Bangladesh. Sci. World J. http://dx.doi.org/10.1155/2014/729418. Ahmed, S., Chauhan, B.S., Humphreys, E., 2013. Effect of application timings of soil applied herbicides on weed growth and crop yield in dry seeded rice in Bangladesh. In: Proceedings of the 24th Asian-Pacific Weed Science Society Conference, Bandung, Indonesia, pp. 462e469. Ahmed, S., Islam, M.R., Alam, M.M., Haque, M.M., Karim, A.J.M.S., 2011. Rice production and profitability as influenced by integrated crop and resources management. Eco-Frien. Agril. J. 11, 720e725. Ahmed, S., Salim, M., Chauhan, B.S., 2014. Effect of weed management and seed rate on crop growth under direct dry seeded rice systems in Bangladesh. PLoS ONE 9 (7). http://dx.doi.org/10.1371/journal.pone.0101919. Ashton, F.M., Crafts, A.S., 1981. Mode of Action of Herbicides. John Wiley and Sons, New York, 525 pp. Bhowmick, M.K., Ghosh, R.K., 2002. Relative efficacy of herbicides against weed incidence in summer rice. Adv. Plant Sci. 34, 192e196. Blackshaw, R.E., Brandt, R.N., Janzen, H.H., Grant, C.A., Derksen, D.A., 2003. Differential response of weed species to added nitrogen. Weed Sci. 51, 532e539. Blackshaw, R.E., O'Donovan, J.T., Harker, K.N., Clayton, G.W., Stougaard, R., 2006. Reduced herbicide doses in field crops: a review. Weed Biol. Manage 6, 10e17. 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. Interaction of rice residue and PRE herbicides on emergence and biomass of four weed species. Weed Technol. 26, 627e632. Chauhan, B.S., Johnson, D.E., 2011a. Growth response of direct-seeded rice to oxadiazon and bispyribac-sodium in aerobic and saturated soils. Weed Sci. 59, 119e122. Chauhan, B.S., Johnson, D.E., 2011b. Row spacing and weed control timing affect yield of aerobic rice. Field Crops Res. 121, 226e231. 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. ~ a, J., 2012. Effect of tillage systems and herbicides on weed Chauhan, B.S., Open emergence, weed growth, and grain yield in dry-seeded rice systems. Field Crops Res. 137, 56e69. Dickmann, R., Melgarelo, J., Loubiere, P., Montagnon, M., 1997. Oxadiargyl: a novel herbicide for rice and sugarcane. In: Proceedings British Crop Protection Conference-weeds, Brighton, UK, pp. 51e57. EFSA, 2013. Reasoned opinion on the review of the existing maximum residue levels (MRLs) for oxadiargyl according to article 12 of regulation (EC) No 396/ 2005. EFSA J. 11 (10), 3441. Gathala, M.K., Ladha, J.K., Kumar, V., Saharawat, Y.S., Kumar, V., Sharma, P.K., Sharma, S., Pathak, H., 2011. Tillage and crop establishment affects sustainability of South Asian riceewheat system. Agron. J. 103, 961e971. Gitsopoulos, T.K., Froud-Williams, R.J., 2004. Effects of oxadiargyl on direct-seeded rice and Echinochloa crus-galli under aerobic and anaerobic conditions. Weed Res. 44, 329e334. Harding, S.S., Taylor, D.R., Jalloh, A.B., Mahmood, N., Dixon, C.A., Johnson, S.D., 2012. Evaluation of the efficacy of different rates of herbicides on weed growth and grain yield of two rice varieties in two rice ecologies in Sierra Leone. Am. J. Exp. Agric. 2, 607e615. Jacques, G.L., Harvey, R.G., 1979. Dinitroaniline herbicide phytotoxicity as influenced by soil moisture and herbicide vaporization. Weed Sci. 27, 536e539. Kato, Y., Katsura, K., 2014. Rice adaptation to aerobic soils: physiological considerations and implications for agronomy. Plant Prod. Sci. 17, 1e12. Khaliq, A., Matloob, A., Ahmed, N., Rasul, F., Awan, I.U., 2012. Post emergence chemical weed control in direct seeded fine rice. J. Ani. Plant Sci. 22, 1101e1106. Kirkland, K.J., Holm, F.A., Stevenson, F.C., 2000. Appropriate crop seeding rate when herbicide rate is reduced. Weed Technol. 14, 692e698. Lee, H.J., Duke, S.O., 1994. Protoporphyrinogen IX-oxidizing activities involved in the mode of action of peroxidizing herbicides. J. Agric. Food Chem. 42, 2610e2618. Levene, B.C., Owen, M.D.K., 1995. Effect of moisture stress and leaf age on bentazon absorption in common cocklebur (Xanthium strumarium) and velvetleaf (Abutilon theophrasti). Weed Sci. 43, 7e12. Mahajan, G., Chauhan, B.S., 2013. Herbicide options for weed control in dry-seeded aromatic rice in India. Weed Technol. 27, 682e689. Mahajan, G., Chauhan, B.S., Gill, M.S., 2013. Dry-seeded rice culture in Punjab state of India: lessons learned from farmers. Field Crops Res. 144, 89e99. Mahajan, G., Poonia, V., Chauhan, B.S., 2014. Integrated Weed management using
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planting pattern, cultivar, and herbicide in dry-seeded rice in Northwest India. Weed Sci. 62, 350e359. 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. Malefyt, T., Duke, W.B., 1984. Pendimethalin phytotoxicity to velvetleaf (Abutilon tbeophrasti) and powell amaranth (Amaranthus powellii). Weed Sci. 32, 520e524. Nethra, N.S., Jagannath, S., 2011. Phytotoxic effect of oxadiargyl on germination and early growth of sunflower (Helianthus annuus L.) and maize (Zea mays L.). Arch. Phytopathol. Plant Prot. 44, 1901e1907. Parka, S.J., Soper, O.F., 1977. The physiology and mode of action of the dinitroaniline herbicides. Weed Sci. 25, 79e87. Phuong, L.T., Denich, M., Vlek, P.L.G., Balasubramanian, V., 2005. Suppressing weeds in direct seeded lowland rice: effects of methods and rates of seeding. J. Agron. Crop Sci. 191, 185e194. Rahman, M., Juraimi, A.S., Suria, J., Azmi, B.M., Anawar, P., 2012. Response of weed flora to different herbicides in aerobic rice system. Sci. Res. Essa 7, 12e23. Ranjit, 2007. Weeds associated with different crops. In: Paper Presented to Training on Weed Management in Rice April 25e27, NARC, Khumaltar, Nepal. Rao, A.N., Johnsson, D.E., Prasad, S.B., Ladha, J.K., Mortimer, A.M., 2007. Weed
management in direct-seeded rice. Adv. Agron. 93, 153e255. Rashid, M.H., Alam, M.M., Rao, A.N., Ladha, J.K., 2012. Comparative efficacy of pretilachlor and hand weeding in managing weeds and improving the productivity and net income of wet-seeded rice in Bangladesh. Field Crops Res. 128, 17e26. Singh, A., Phogat, V.K., Dahiya, R., Batra, S.D., 2014. Impact of long-term zero till wheat on soil physical properties and wheat productivity under riceewheat cropping system. Soil Till. Res. 140, 98e105. Singh, S., Bhushan, L., Ladha, J.K., Gupta, R.K., Rao, A.N., Sivaprasad, B., 2006. Weed management in dry seeded rice (Oryza sativa L.) cultivated in the furrow irrigated raised bed planting system. Crop Prot. 25, 487e495. Sinha, S.N., Agnihotri, N.P., Gajbhiye, V.T., 1996. Field evaluation of pendimethalin for weed control in onion and persistence in plant and soil. Ann. Plant Prot. Sci. 4, 71e75. Smith, M.A.K., 2004. Pendimethalin phytotoxicity and seedling weed control in Indian spinach (Basella alba L.). Crop Prot. 23, 201e204. Tsiropoulos, N.G., Miliadis, G.E.S., 1998. Field persistence study of pendimethalin in soils after herbicide post emergence application in onion cultivation. J. Agric. Food Chem. 46, 291e295. Zhang, J., Weaver, S.E., Hamill, A.S., 2000. Risks and reliability of using herbicides at below-labeled doses. Weed Technol. 14, 106e115.
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Efficacy and phytotoxicity of different rates of oxadiargyl and pendimethalin in dry-seeded rice (Oryza sativa L.) in Bangladesh Sharif Ahmed a, *, Bhagirath Singh Chauhan b a b
~ os, Philippines International Rice Research Institute, Los Ban 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 27 January 2015 Received in revised form 22 March 2015 Accepted 23 March 2015 Available online 27 March 2015
A field study was established to evaluate oxadiargyl and pendimethalin during the wet seasons in Bangladesh in 2012 and 2013. The study evaluated the following treatments: oxadiargyl applied at 80, 120, and 160 g ai ha1; pendimethalin at 800, 1200, and 1600 g ai ha1; partial weedy; and weed-free. Rice plant density was greatly affected by weed control treatment. Lower density and lower uniformity of the rice plant stand occurred as a result of increased rates of herbicides. Increased rates of pendimethalin were more toxic than increased rates of oxadiargyl. Both herbicides effectively controlled Digitaria ciliaris, Echinochloa colona, and Phyllanthus niruri; however, they were unable to control Murdannia nudiflora. Oxadiargyl controlled Cyperus rotundus across rates by 31e55%, but pendimethalin was completely ineffective on it, and higher rates of both herbicides had no effect in controlling this weed. Both herbicides at higher rates reduced total weed biomass significantly. Among herbicide treatments, the highest yield (3.7e4.0 t ha1) was recorded in plots treated with oxadiargyl at 160 g ai ha1 and the lowest yield (2.4e2.8 t ha1) was in plots treated with pendimethalin at 1600 g ai ha1. Results from our study suggest that a higher rate of oxadiargyl can increase yield by suppressing weeds in dry-seeded rice systems. Similar to the results of oxadiargyl, pendimethalin at higher rates also greatly suppressed weeds; however, yield decreased due to phytotoxicity to rice seedlings. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Herbicide rate Plant density Plant injury Weeds density Weed biomass Rice yield
1. Introduction Dry-seeded rice (DSR) is an alternative labor- and water-saving rice production system. Because of farm labor and irrigation water shortage, farmers in some Asian countries are becoming interested in dry-seeded rice systems (Ahmed and Chauhan, 2014; Kato and Katsura, 2014; Mahajan et al., 2013). This system of rice establishment is conducive to mechanization and there is no need for puddling (land preparation in standing water) and transplanting which are needed for conventional transplanted rice systems. In addition to saving labor and water, dry-seeded rice improves the soil physical and chemical properties, which facilitate the growth and yield of non-rice crops grown in rotation with rice (Gathala et al., 2011; Singh et al., 2014). Despite the multiple benefits of dry-seeded rice, weed management is a major challenge to the success of these systems (Chauhan and Johnson, 2011a; Rao et al., 2007). Weeds are
* Corresponding author. E-mail address: [email protected] (S. Ahmed). http://dx.doi.org/10.1016/j.cropro.2015.03.021 0261-2194/© 2015 Elsevier Ltd. All rights reserved.
comparatively greater in number in this system than in traditional transplanted rice, because of the simultaneous emergence of rice and weeds and the absence of standing water at this stage (Chauhan, 2012; Rao et al., 2007). Inherently, weeds are more competitive in nutrients and they grow faster than the crop (Blackshaw et al., 2003). If weeds are not controlled in dry-seeded systems, yield loss can be greater than 90% (Chauhan and Johnson, 2011b). Yield loss in dry-seeded systems depends on weed infestation level and varies from country to country; for example, yield loss is up to 93% in Nepal (Ranjit, 2007), more than 80% in Pakistan (Khaliq et al., 2012), more than 70% in the Philippines (Chauhan and ~ a, 2012; Phoung et al., 2005), and up to 78% in Bangladesh Open (Ahmed et al., 2014). Therefore, weed management is an important prerequisite in dry-seeded systems. In Bangladesh, weeding by hand is the common practice of controlling weeds; however, this method is becoming impractical because of labor shortage and high labor cost (Ahmed et al., 2011). In addition, hand weeding is difficult at early growth stages, because of the similar morphology of some weeds with rice, such as Echinochloa spp., and Leptochloa chinensis (Ahmed and Chauhan,
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2014; Rahman et al., 2012). Chemical weed control is now available and applications of pre-emergence herbicides offer weed control from the beginning of the crop, facilitating a head start and competitive advantage to the crop (Rahman et al., 2012). Therefore, the use of pre-emergence herbicides is a good option to achieve effective weed control and higher yield in DSR systems (Mahajan and Chauhan, 2013). Herbicides with pre-emergence activity, such as oxadiazon, oxadiargyl, pendimethalin, butachlor, thiobencarb, and oxyfluorfen are available around the world and are commonly used in dry-seeded rice (Chauhan et al., 2012). A recent study in dry-seeded rice found that oxadiargyl and pendimethalin are the most effective pre-emergence herbicides among the available herbicides in Bangladesh (Ahmed and Chauhan, 2014). Oxadiargyl inhibits protoporphyrinogen oxidase, the enzyme that converts protoporphyrinogen IX into protoporphyrin IX, causing rapid membrane peroxidation and cellular death (Dickmann et al., 1997; Lee and Duke, 1994). It works through contact with emerging or recently emerged shoots, but there is slight absorption by the root (Nethra and Jagannath, 2011). Oxadiargyl is commonly used to control annual grasses, sedges, and broadleaf weeds in a range of crops, such as Oryza sativa, Saccharum spontaneum, Helianthus annuus, transplanted vegetables, and perennial crops (Dickmann et al., 1997; EFSA, 2013). Pendimethalin inhibits microtubulin synthesis, which is necessary in the formation of cell walls and in chromosome movement during mitosis (Parka and Soper, 1977). These herbicides are absorbed to a smaller extent by plant root systems and, to a greater extent, by young shoot organs, such as the hypocotyl or coleoptiles (Ashton and Crafts, 1981; Malefyt and Duke, 1984). Pendimethalin is used in the selective control of grass and broadleaf weeds in Zea mays, Glycine max, Allium spp, and Gossypium birsutum (Bhowmick and Ghosh, 2002; Sinha et al., 1996; Tsiropoulos and Miliadis, 1998). Oxadiargyl and pendimethalin are effective pre-emergence herbicides, which are used to control common weeds in dryseeded rice systems. However, the efficacy and phytotoxicity of herbicides with soil activity depend on environmental conditions, application timing, and spray techniques (Jacques and Harvey, 1979; Levene and Owen, 1995). In addition to this, an appropriate herbicide rate is very important in achieving adequate weed control and reducing crop phytotoxicity (Harding et al., 2012). Herbicide rates depend on several factors, including weed seed bank size, presence or absence of residue and soil properties (Blackshaw et al., 2006; Chauhan and Abugho, 2012; Zhang et al., 2000). Previous studies in several crops under different environmental conditions found substantial variations in weed control with different herbicide rates (Zhang et al., 2000). A previous study reported that a high rate of oxadiargyl applied at 150 g ai ha1 caused seedling mortality in rice in anaerobic conditions but not in aerobic conditions (Gitsopoulos and FroudWilliams, 2004). Smith (2004) reported that the application of pendimethalin at rates of 990e1980 g ai ha1 controlled weeds in Basella alba, but the crop was stunted with dark-green color, swollen stem, and sunken mottled leaves. On the contrary, lower pendimethalin rates of 330e660 g ai ha1 were less effective against weeds, and the growth and biomass production of the crop were not affected. In Bangladesh, herbicides used as a pre-emergence in dryseeded systems are based on the recommendations for transplanted rice. In this system, pre-emergence herbicides are applied under moist soil conditions but in transplanted rice systems, they are applied under standing water conditions (Rashid et al., 2012). In addition, Bangladeshi farmers are not concerned about the proper dose of herbicides. Although oxadiargyl and pendimethalin are widely used in dry-seeded rice, information on the effect of different rates of these two herbicides on weeds and rice is limited.
Therefore, this study was established to evaluate the comparative performance of oxadiargyl and pendimethalin at different rates on weed control and crop response in dry-seeded rice systems. 2. Materials and methods A field study was conducted to evaluate the efficacy and phytotoxicity of oxadiargyl and pendimethalin in a dry-seeded system at the Regional Agricultural Research Station in Bangladesh Agricultural Research Institute, Jessore, in the wet (aman) seasons, of 2012 and 2013. The area belongs to agroecological zone number 11, known as the High Ganges River Floodplain. The climate of the area is subtropical, with an average annual rainfall of 1590 mm, minimum temperatures of 6e9 C in January, and maximum temperatures of 36e44 C in AprileMay. The minimum and maximum temperatures and amount of rainfall recorded at the experimental site during the experimental periods are presented in Fig. 1. The soil to a depth of 0e15 cm was clay loam (sand of 31%, silt of 32%, and clay of 37%), with a bulk density of 1.58 g cm3, pH of 7.8, and carbon content of 1%. The study was arranged in a randomised completed block design with three replications. The plot size was 4.5 m 3 m. Eight weed control treatments were included in each season: oxadiargyl applied at 80, 120, and 160 g ai ha1; pendimethalin applied at 800, 1200, and 1600 g ai ha1; partial weedy; and weed-free. Herbicides were applied 2 days after sowing (DAS) using a knapsack sprayer attached with three flat-fan nozzles on a boom, the sprayer delivering 450 L solution ha1. At spraying, the soil was saturated and the next irrigation was applied four days after the spray. Weed-free plots were hand weeded four times at 15, 30, 45, and 70 DAS. In the partial weedy plots, one hand weeding was performed at 40 DAS and weeds were allowed to grow before and after hand weeding. BRRI dhan49 rice was sown at a seeding rate of 40 kg ha1 and a row spacing of 20 cm, using a power tiller operated seed-drill fitted with a fluted-type seed metering device. The crop was sown on June 17 in both years. Fertilizers such as NePeKeSeZn were applied at the rates of 120e15e48e12e2.2 kg ha1 in the form of urea, triple superphosphate (TSP), potassium chloride (KCl),
Fig. 1. Maximum and minimum temperatures and total rainfall (mm) recorded at the experimental site in the aman seasons of 2012 and 2013.
S. Ahmed, B.S. Chauhan / Crop Protection 72 (2015) 169e174
calcium sulphate (gypsum), and zinc sulphate, respectively. Full doses of TSP, MoP, gypsum, and zinc sulphate were applied immediately before sowing. Urea was applied in four equal splits at 14 DAS, at active tillering (30 DAS), at maximum tillering (45 DAS), and at panicle initiation (65 DAS). Immediately after sowing, the field was surface irrigated. After this, irrigation was based on tensiometer readings using a threshold value of 15 kPa at 15-cm soil depth. At each irrigation, a 5 cm flood was established. At 50 DAS, the fungicide tebuconazole plus trifloxystrobin 300 g ai ha1 (Nativo 75 WP, Bayer CropScience Limited, Bangladesh) was applied to control blast, and fipronil 3G 300 g ai ha1 (Regent 3 GR, BASF Bangladesh Limited) was applied at 70 DAS to control stem borers. To evaluate herbicide phytotoxicity in rice, rice plants were counted at 14 DAS from four randomly selected 1-m row lengths in each plot and the reduction (%) in plant stands was calculated by comparing with the non-treated check. The non-uniformity of plant establishment due to herbicide toxicity was determined as the coefficient of variation of means of the 12 rows (4 rows 3 replicates) for each treatment combination. To evaluate the performance of herbicides on individual weed species, weed density and weed biomass were measured at 40 DAS by randomly placing two quadrats, measuring 40 cm by 40 cm, in each plot. Weeds were separated by species, counted, and their biomass was measured after oven drying the samples at 70 C for 72 h. To evaluate the effect of weeds on rice, weed and rice biomass were measured from two 40 cm by 40 cm quadrats at 50% flowering. At harvest, rice panicles were counted from four randomly placed 1-m row lengths in each plot. Rice grain yield was determined from a harvested area of 4.0 m 2.2 m. Grain yield was converted to t ha1 at 14% moisture content. Data were analyzed using analysis of variance (ANOVA) to evaluate differences between treatments, and means were separated using the least significant difference (LSD) at 5% (Crop Stat 7.2; International Rice Research Institute, Philippines). In a combined analysis of data, the interaction between years and treatments was significant; therefore, the data were presented separately for each year. Weed density and biomass data were transformed using square root transformation [√(x þ 0.5)] before analysis. Transformation, did not improve homogeneity. Therefore, the original values were used for analysis and presentation. 3. Results and discussion 3.1. Rice plant density, stands reduction (%), and uniformity Rice plant density was strongly influenced (p < 0.05) by weed control treatments in both years (Table 1). Compared with the non-
Table 1 Effect of weed control treatments on rice plant density (number m2), plant stands reduction (%), and coefficient of variation (%) at 14 d after sowing in the aman seasons of 2012 and 2013. Treatment
Plant density (no. m2)
Plant stands reduction (%)
Coefficient of variation (%)
Herbicide rate (g ai ha1)
2012
2013
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy Weed-free LSD0.05
202 193 184 187 159 128 207 208 8
174 171 156 160 138 115 173 176 11
3 7 12 10 23 39 0 0 9
0 2 11 9 21 34 0 0 7
8.9 10.0 12.3 11.3 14.3 18.1 8.1 6.1 4.8
10.0 10.5 15.7 13.9 16.5 20.4 7.7 8.5 6.5
171
treated checks (weed-free and partial weedy), lower plant densities in both years were recorded when rice was treated with pendimethalin at different rates. Rice treated with pendimethalin applied at 800 g ai ha1 had 9e10% lower plant stands, compared with the non-treated (weed-free) check. However, these reductions were 21e23% and 34e39% for the rice treated with pendimethalin at 1200 and 1600 g ai ha1, respectively. In previous studies, Ahmed et al. (2013) and Ahmed and Chauhan (2014) reported the phytotoxicity of pendimethalin in dry-seeded systems. Rice treated with oxadiargyl applied at 80 and 120 g ai ha1 had similar plant density with that of non-treated rice; however, oxadiargyl applied at 160 g ai ha1 reduced plant density significantly. These results were inconsistent with the previous study of Gitsopoulos and Froud-Williams (2004), who reported that oxadiargyl applied at 150 g ai ha1 did not cause mortality in aerobic conditions, but caused crop injury in anaerobic conditions. This study suggests that in dry-seeded systems, pendimethalin can cause phytotoxicity to rice plants when applied at 800 g ai ha1; however, rates higher than this can be more toxic. Because of the phytotoxicity of higher rates of pendimethalin, the uniformity of the crop stand was also affected. Rice plant density had a higher variability when treated with high rates of each herbicide (Table 1). It was observed that higher rates of herbicides did not impair the emergence of rice plants, but toxicity occurred immediately after emergence (visual observations). Common toxicity symptoms for both herbicides included stunting, slower growth, and necrosis on the main culm and leaves of rice. 3.2. Weed density and biomass The common weed species found at the experimental site were Ageratum conyzoides, Cleome rutidosperma, Celosia argentea, Cyperus rotundus, Dactyloctenium aegyptium, Digitaria ciliaris, Echinochloa colona, Eleusine indica, Galinsoga ciliate, Murdannia nudiflora and Phyllanthus niruri. Results were presented only for the top five dominant species because of non-uniform distribution of other weed species. At 40 DAS, the density (Table 2) and biomass (Table 3) of individual weed species, except M. nudiflora were affected by weed control treatments. Oxadiargyl at 80 g ai ha1 reduced C. rotundus density and biomass; however, there was no additional benefit of using higher rates. Compared with the partial weedy rice, oxadiargyl across rates reduced C. rotundus density by 31e55% and biomass by 41e55%. Pendimethalin failed to provide any control of C. rotundus, even at the highest rate. Pendimethalin controlled D. ciliaris better than oxadiargyl. Compared with the partial weedy rice, oxadiargyl was unable to control D. ciliaris density and biomass when applied at 80 g ai ha1; however, the higher rates, 120 and 160 g ai ha1, were able to provide significant control. E. colona was the most dominant weed species in both seasons, and its density was strongly influenced by weed control treatments. Different rates of pendimethalin and oxadiargyl controlled this weed density by more than 80%; however, pendimethalin was more effective than oxadiargyl. E. colona density was reduced by 90e91%, 94e97%, and 99e100% with pendimethalin rates of 800, 1200, and 1600 g ai ha1, respectively, compared with the partial weedy plots. Similarly, oxadiargyl at 80 and 120 g ai ha1 reduced the density of E. colona by 70e76% and 81e83%, respectively. There was no additional benefit to further increase in herbicide dose to 160 g ai ha1. Reduction in biomass followed a trend similar to that for density (Table 3). The density and biomass of P. niruri was reduced by herbicide treatments, and oxadiargyl performed better than pendimethalin (Tables 2 and 3). Compared with the partial weedy plots, across rates, oxadiargyl reduced P. niruri density by 90e100%. On the other hand, pendimethalin reduced P. niruri density by 62e69% when
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Table 2 Effect of weed control treatments on density (number m2) of different weed species at 40 d after sowing in the aman seasons of 2012 and 2013. Treatment
Weed density (no. m2) Cyperus rotundus
Digitaria ciliaris
Echinochloa colona
Murdannia nudiflora
Phyllanthus niruri
Total
Herbicide rate (g ai ha1)
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy LSD 0.05
54 57 51 110 100 123 113 38
128 132 122 189 190 178 192 33
37 19 12 18 7 6 48 12
32 17 15 15 9 0 40 9
45 39 33 17 5 0 194 23
56 38 34 18 11 2 189 12
28 23 26 33 29 34 33 NS
36 37 32 37 43 42 42 NS
5 0 0 22 8 0 58 6
5 0 0 17 8 4 53 7
169 138 122 200 149 163 446 53
257 224 203 276 261 226 516 65
Table 3 Effect of weed control treatments on biomass (g m2) of different weed species at 40 d after sowing in the aman seasons of 2012 and 2013. Treatment
Weed biomass (g m2) Cyperus rotundus
Digitaria ciliaris
Echinochloa colona
Murdannia nudiflora
Phyllanthus niruri
Total
Herbicide rate (g ai ha1)
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy LSD0.05
10 10 8 21 20 20 18 7
18 17 15 27 25 26 32 4
5 3 1 3 1 1 8 4
4 2 2 3 1 0 6 3
14 9 9 3 2 0 44 5
11 7 7 7 4 1 38 4
2 3 2 3 3 4 3 NS
3 4 3 5 5 4 6 NS
1 0 0 4 1 0 9 3
1 0 0 4 1 0 10 1
32 25 20 34 27 25 82 8
37 30 27 46 36 31 92 9
applied at 800 g ai ha1, but it provided 84e100% control at the rates of 1200 and 1600 g ai ha1. Herbicide treatments reduced the density and biomass of total weeds. Compared with the partial weedy treatment, oxadiargyl at different rates reduced weed density by 50e73% (Table 2) and biomass by 60e76% (Table 3). Similar to the results of oxadiargyl, pendimethalin reduced weed density and biomass by 47e66% and 51e70%, respectively. Increased rates of oxadiargyl and pendimethalin did not reduce total weed density; however, they reduced biomass significantly in both years. In dry-seeded rice systems, pre-emergence herbicides are considered the best weed management tool because they provide a head-start to the crop as compared to weeds as the crop emerges in a weed-free environment (Ahmed and Chauhan, 2014; Mahajan et al., 2014; Mahajan and Timsina, 2011; Singh et al., 2006). Pendimethalin and oxadiargyl are widely used in these systems to control grass, broadleaf, and sedge weeds (Gitsopoulos and FroudWilliams, 2004). In this study, oxadiargyl and pendimethalin applied at rates higher than the recommended were more effective against grass weeds, and these results are supported by a previous study (Kirkland et al., 2000). In the previous study, grass weed control was lower when herbicide rates were reduced.
treatment, weed biomass decreased by 27e31% and 12e16%, and rice biomass increased by 6e7% and 2e5% when herbicide dose increased from 80 to 120 or 160 g ai ha1, respectively. Similarly, weed biomass decreased by 33e43% and 21e30% and rice biomass decreased by 11e17% and 37e41% when pendimethalin rates increased from 800 to 1200 or 1600 g ai ha1, respectively.
3.3. Rice and weed biomass at 50% crop flowering
3.4. Rice panicle number
Rice and weed biomass were influenced by herbicide treatment at 50% crop flowering (Table 4). There was a trend of increasing rice biomass with decreasing weed biomass, except for the pendimethalin 1200 and 1600 g ai ha1 treatments. At this stage, the highest weed biomass of 168e182 g m2 and least rice biomass of 296e333 g m2 were found in the partial weedy plots. The lowest weed biomass of 70e81 g m2 was recorded in the pendimethalin 1600 g ai ha1 treatment, which was 58% lower in 2012 and 56% lower in 2013 than the partial weedy treatment. In the oxadiargyl
Rice panicle number was always higher in the season-long weed-free rice and lower in the partial weedy plots (Table 5). All herbicide treatments had a significantly lower panicle number than the weed-free treatment. Between the herbicides, in oxadiargyl treatments, panicle number increased significantly with increase in herbicide rate from 80 to 120 g ai ha1; however, no further increment was observed at 160 g ai ha1. In the pendimethalin treatments, these results were reversed and panicle number decreased with increase in rate. Compared with pendimethalin at
Table 4 Effect of weed control treatments on rice biomass (g m2) and weed biomass (g m2) at 50% crop flowering in the aman seasons of 2012 and 2013. Treatment
Rice biomass (g m2)
Weed biomass (g m2)
Herbicide rate (g ai ha1)
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy Weed-free LSD0.05
575 600 612 558 528 469 333 806 49
542 556 583 523 505 420 296 776 92
123 102 91 125 96 70 168 e 19
137 120 100 143 103 81 182 e 16
S. Ahmed, B.S. Chauhan / Crop Protection 72 (2015) 169e174 Table 5 Effect of weed control treatments on rice panicles (number m2) and rice grain yield (g m2) at harvest in the aman seasons of 2012 and 2013. Treatment
Rice panicles (no. m2)
Rice grain yield (t ha1)
Herbicide rate (g ai ha1)
2012
2013
2012
2013
Oxadiargyl 80 Oxadiargyl 120 Oxadiargyl 160 Pendimethalin 800 Pendimethalin 1200 Pendimethalin 1600 Partial weedy Weed-free LSD0.05
296 328 339 305 292 241 202 381 22
276 308 319 282 270 230 187 352 28
3.4 3.8 4.0 3.5 3.2 2.8 2.1 5.0 0.4
3.1 3.6 3.7 3.2 3.0 2.4 1.8 4.8 0.4
800 g ai ha1, pendimethalin applied at 1200 g ai ha1 did not reduce panicle number but pendimethalin at 1600 g ai ha1 reduced the panicles (18e21%) significantly. 3.5. Rice grain yield Similar to rice panicle number, rice grain yield was also greatly affected by weed control treatment (Table 5). In the herbicidetreated plots, yield was 24e53% higher than in the partial weedy treatment, but 20e48% lower than in the season-long weed-free treatment. In oxadiargyl treatments, yield increased by 14e21% when herbicide rate increased from 80 to 120 or 160 g ai ha1, and this response was observed because higher rates of oxadiargyl controlled weeds better than the lower rate. Pendimethalin rates higher than the recommended rate (e.g., 800 g ai ha1) were more effective against weeds, but this caused a decrease in yield. This was due to crop toxicity at higher rates, resulting in hampered uniformity of the plant population. Singh et al. (2006) similarly reported that increased triclopyr rate from 1000 to 1500 g ha1 was better in reducing weed density and biomass; however, due to phytotoxicity in rice, it resulted in a reduced yield. Oxadiargyl rate, increased from 80 to 120 g ai ha1, was not toxic to rice, and it effectively controlled weeds as well as produced higher yield. The application of pre-emergence herbicides is the best weed management component considered in dry-seeded systems (Mahajan et al., 2014). However, the weed control efficiency of preemergence herbicides depends on proper herbicide doses, application timing, soil water content, and the extent of the weed seed bank (Chauhan, 2012). The results of this study suggest that the pre-emergence herbicide oxadiargyl at a higher rate than the recommended (80 g ai ha1) controlled weeds more effectively and resulted in a higher crop yield. Pendimethalin rates higher than the recommended rate (800 g ai ha1) effectively controlled weeds but resulted in lower crop yield due to phytotoxicity. In this study, we used oxadiargyl and pendimethalin at recommended and higher rates. The objective was to assess the benefits and risks of higher rates of pre-emergence herbicides, which might be helpful in cautioning and making recommendations for farmers who grow dry-seeded rice. However, in this study, we did not use any rate of herbicides lower than the recommended rate, and did not consider cost-effectiveness. But, for farmers, cost-effectiveness is very important. Therefore, further research is needed to evaluate the economics of pre-emergence herbicides at different rates in different soil and environmental conditions. Acknowledgments ~ as for providing We would like to thank Ms. Priscilla Grace Can comments on the manuscript. We also gratefully acknowledge the
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support of the International Fund for Agricultural Development (IFAD); the Cereal Systems Initiative for South Asia (CSISABangladesh); and the Bangladesh Agricultural Research Institute (BARI), Regional Agricultural Research Station at (RARS) Jessore. We especially thank A.K.M. Ferdous of the CSISA-Jessore Hub for his continuous support, and research assistants Alamin, Anwara, and Rima. We also thank all permanent technicians for their admirable technical support.
References Ahmed, S., Chauhan, B.S., 2014. Performance of different herbicides in dry-seeded rice in Bangladesh. Sci. World J. http://dx.doi.org/10.1155/2014/729418. Ahmed, S., Chauhan, B.S., Humphreys, E., 2013. Effect of application timings of soil applied herbicides on weed growth and crop yield in dry seeded rice in Bangladesh. In: Proceedings of the 24th Asian-Pacific Weed Science Society Conference, Bandung, Indonesia, pp. 462e469. Ahmed, S., Islam, M.R., Alam, M.M., Haque, M.M., Karim, A.J.M.S., 2011. Rice production and profitability as influenced by integrated crop and resources management. Eco-Frien. Agril. J. 11, 720e725. Ahmed, S., Salim, M., Chauhan, B.S., 2014. Effect of weed management and seed rate on crop growth under direct dry seeded rice systems in Bangladesh. PLoS ONE 9 (7). http://dx.doi.org/10.1371/journal.pone.0101919. Ashton, F.M., Crafts, A.S., 1981. Mode of Action of Herbicides. John Wiley and Sons, New York, 525 pp. Bhowmick, M.K., Ghosh, R.K., 2002. Relative efficacy of herbicides against weed incidence in summer rice. Adv. Plant Sci. 34, 192e196. Blackshaw, R.E., Brandt, R.N., Janzen, H.H., Grant, C.A., Derksen, D.A., 2003. Differential response of weed species to added nitrogen. Weed Sci. 51, 532e539. Blackshaw, R.E., O'Donovan, J.T., Harker, K.N., Clayton, G.W., Stougaard, R., 2006. Reduced herbicide doses in field crops: a review. Weed Biol. Manage 6, 10e17. 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. Interaction of rice residue and PRE herbicides on emergence and biomass of four weed species. Weed Technol. 26, 627e632. Chauhan, B.S., Johnson, D.E., 2011a. Growth response of direct-seeded rice to oxadiazon and bispyribac-sodium in aerobic and saturated soils. Weed Sci. 59, 119e122. Chauhan, B.S., Johnson, D.E., 2011b. Row spacing and weed control timing affect yield of aerobic rice. Field Crops Res. 121, 226e231. 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. ~ a, J., 2012. Effect of tillage systems and herbicides on weed Chauhan, B.S., Open emergence, weed growth, and grain yield in dry-seeded rice systems. Field Crops Res. 137, 56e69. Dickmann, R., Melgarelo, J., Loubiere, P., Montagnon, M., 1997. Oxadiargyl: a novel herbicide for rice and sugarcane. In: Proceedings British Crop Protection Conference-weeds, Brighton, UK, pp. 51e57. EFSA, 2013. Reasoned opinion on the review of the existing maximum residue levels (MRLs) for oxadiargyl according to article 12 of regulation (EC) No 396/ 2005. EFSA J. 11 (10), 3441. Gathala, M.K., Ladha, J.K., Kumar, V., Saharawat, Y.S., Kumar, V., Sharma, P.K., Sharma, S., Pathak, H., 2011. Tillage and crop establishment affects sustainability of South Asian riceewheat system. Agron. J. 103, 961e971. Gitsopoulos, T.K., Froud-Williams, R.J., 2004. Effects of oxadiargyl on direct-seeded rice and Echinochloa crus-galli under aerobic and anaerobic conditions. Weed Res. 44, 329e334. Harding, S.S., Taylor, D.R., Jalloh, A.B., Mahmood, N., Dixon, C.A., Johnson, S.D., 2012. Evaluation of the efficacy of different rates of herbicides on weed growth and grain yield of two rice varieties in two rice ecologies in Sierra Leone. Am. J. Exp. Agric. 2, 607e615. Jacques, G.L., Harvey, R.G., 1979. Dinitroaniline herbicide phytotoxicity as influenced by soil moisture and herbicide vaporization. Weed Sci. 27, 536e539. Kato, Y., Katsura, K., 2014. Rice adaptation to aerobic soils: physiological considerations and implications for agronomy. Plant Prod. Sci. 17, 1e12. Khaliq, A., Matloob, A., Ahmed, N., Rasul, F., Awan, I.U., 2012. Post emergence chemical weed control in direct seeded fine rice. J. Ani. Plant Sci. 22, 1101e1106. Kirkland, K.J., Holm, F.A., Stevenson, F.C., 2000. Appropriate crop seeding rate when herbicide rate is reduced. Weed Technol. 14, 692e698. Lee, H.J., Duke, S.O., 1994. Protoporphyrinogen IX-oxidizing activities involved in the mode of action of peroxidizing herbicides. J. Agric. Food Chem. 42, 2610e2618. Levene, B.C., Owen, M.D.K., 1995. Effect of moisture stress and leaf age on bentazon absorption in common cocklebur (Xanthium strumarium) and velvetleaf (Abutilon theophrasti). Weed Sci. 43, 7e12. Mahajan, G., Chauhan, B.S., 2013. Herbicide options for weed control in dry-seeded aromatic rice in India. Weed Technol. 27, 682e689. Mahajan, G., Chauhan, B.S., Gill, M.S., 2013. Dry-seeded rice culture in Punjab state of India: lessons learned from farmers. Field Crops Res. 144, 89e99. Mahajan, G., Poonia, V., Chauhan, B.S., 2014. Integrated Weed management using
174
S. Ahmed, B.S. Chauhan / Crop Protection 72 (2015) 169e174
planting pattern, cultivar, and herbicide in dry-seeded rice in Northwest India. Weed Sci. 62, 350e359. 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. Malefyt, T., Duke, W.B., 1984. Pendimethalin phytotoxicity to velvetleaf (Abutilon tbeophrasti) and powell amaranth (Amaranthus powellii). Weed Sci. 32, 520e524. Nethra, N.S., Jagannath, S., 2011. Phytotoxic effect of oxadiargyl on germination and early growth of sunflower (Helianthus annuus L.) and maize (Zea mays L.). Arch. Phytopathol. Plant Prot. 44, 1901e1907. Parka, S.J., Soper, O.F., 1977. The physiology and mode of action of the dinitroaniline herbicides. Weed Sci. 25, 79e87. Phuong, L.T., Denich, M., Vlek, P.L.G., Balasubramanian, V., 2005. Suppressing weeds in direct seeded lowland rice: effects of methods and rates of seeding. J. Agron. Crop Sci. 191, 185e194. Rahman, M., Juraimi, A.S., Suria, J., Azmi, B.M., Anawar, P., 2012. Response of weed flora to different herbicides in aerobic rice system. Sci. Res. Essa 7, 12e23. Ranjit, 2007. Weeds associated with different crops. In: Paper Presented to Training on Weed Management in Rice April 25e27, NARC, Khumaltar, Nepal. Rao, A.N., Johnsson, D.E., Prasad, S.B., Ladha, J.K., Mortimer, A.M., 2007. Weed
management in direct-seeded rice. Adv. Agron. 93, 153e255. Rashid, M.H., Alam, M.M., Rao, A.N., Ladha, J.K., 2012. Comparative efficacy of pretilachlor and hand weeding in managing weeds and improving the productivity and net income of wet-seeded rice in Bangladesh. Field Crops Res. 128, 17e26. Singh, A., Phogat, V.K., Dahiya, R., Batra, S.D., 2014. Impact of long-term zero till wheat on soil physical properties and wheat productivity under riceewheat cropping system. Soil Till. Res. 140, 98e105. Singh, S., Bhushan, L., Ladha, J.K., Gupta, R.K., Rao, A.N., Sivaprasad, B., 2006. Weed management in dry seeded rice (Oryza sativa L.) cultivated in the furrow irrigated raised bed planting system. Crop Prot. 25, 487e495. Sinha, S.N., Agnihotri, N.P., Gajbhiye, V.T., 1996. Field evaluation of pendimethalin for weed control in onion and persistence in plant and soil. Ann. Plant Prot. Sci. 4, 71e75. Smith, M.A.K., 2004. Pendimethalin phytotoxicity and seedling weed control in Indian spinach (Basella alba L.). Crop Prot. 23, 201e204. Tsiropoulos, N.G., Miliadis, G.E.S., 1998. Field persistence study of pendimethalin in soils after herbicide post emergence application in onion cultivation. J. Agric. Food Chem. 46, 291e295. Zhang, J., Weaver, S.E., Hamill, A.S., 2000. Risks and reliability of using herbicides at below-labeled doses. Weed Technol. 14, 106e115.