Till now, herbicide seems to be a cost effective tool from an agronomic view point to control weeds. But long term efficacy and sustainability issues are the driving forces behind the reconsideration of herbicide dependent weed management strategy in rice. This demands reappearance of physical and cultural management options combined with judicious herbicide application in a more comprehensive and integrated way. Keeping those in mind, some agronomic tools along with different manual weeding and herbicides combinations were evaluated for their weed control efficacy in rice under aerobic soil conditions. Combination of competitive variety, higher seeding rate, and seed priming resulted in more competitive cropping system in favor of rice, which was reflected in lower weed pressure, higher weed control efficiency, and better yield. Most of the herbicides exhibited excellent weed control efficiency. Treatments comprising only herbicides required less cost involvement but produced higher net benefit. On the contrary, treatments comprising both herbicide and manual weeding required high cost involvement and thus produced lower net benefit. Therefore, adoption of competitive rice variety, higher seed rate, and seed priming along with spraying different early-postemergence herbicides in rotation at 10 days after seeding (DAS) followed by a manual weeding at 30 DAS may be recommended from sustainability view point.
Weeds are endemic in crops [
In response to aforesaid problems, rice farming has been challenged to adopt a weed management strategy more respectful for environment. Weed management continues to be a huge challenge in aerobic rice which is highly vulnerable to weed infestation because of dry ploughing and aerobic soil conditions [
Although weed management is herbicide dominated in many rice belts, there are strong indications that it will change in future [
In rice, many studies have been conducted on IWM, most of which have looked at one or two of those components in isolation. Since the concept of aerobic rice is new, IWM issue is yet to be addressed properly considering the diverse weed management approaches. Therefore, for designing a sustainable weed management strategy for aerobic rice, it is a prerequisite to assess the simultaneous effect of different agronomic practices combined with timely herbicide application. The present study was, therefore, conducted to find out suitable herbicide and manual weeding combination(s) simultaneously incorporated with different agronomic practices to provide a comprehensive integrated weed management system for aerobic rice variety AERON 1.
The field trials were conducted in main season 2010/2011 (November–January) and off season 2011 (May–July) at Universiti Putra Malaysia, Malaysia (3°00′ 21.34′′N, 101°42′ 15.06′′E, and 37 m elevation). The experimental soil (Serdang series) was sandy clay loam in texture (56.77% sand, 21.30% silt, and 21.93% clay) and acidic in reaction (pH 5.6) with 1.42 g cc−1 bulk density, 1.77% organic carbon, and 17.24 me 100 g−1 soil CEC. Soil contained 0.38% total N, 21.5 ppm available P, 139 ppm available K, 803 ppm Ca, and 159 ppm Mg. At field capacity, soil water retention was 22.69% (wet basis) and 29.35% (dry basis). The local climate was hot humid tropic with plentiful rainfall. During the experimental period, average maximum and minimum temperatures, relative humidity, rainfall, evaporation, and sunshine hours ranged from 31.7 to 35.0°C and 22.9 to 24.4°C, 93.5 to 94.7%, 3.8 to 9.9 mm day−1, 2.94 to 4.82 mm day−1 and 3.95 to 6.97 hrs day−1, respectively.
Aerobic rice variety AERON 1 was used as the plant material in the present study. This variety is sourced from International Rice Research Institute (IRRI).
The experiment was laid out in a randomized complete block design with three replications. Fourteen different combinations of herbicides and manual weeding were evaluated for their efficacy in controlling weeds under aerobic soil conditions; season-long weed-free check and season-long weedy check were also included in the trial (Table
List of weed control treatments used in the experiments in main season 2010/11 and off season 2011.
Label | Treatments | Application rate | Time |
---|---|---|---|
T1 | Pretilachlor/safener fb bentazon/MCPA | 0.5 kg a.i./ha fb 0.6/0.1 kg a.i./ha | 1 fb 30 |
T2 | Pretilachlor/safener fb MW | 0.5 kg a.i./ha | 10 fb 30 |
T3 | Pretilachlor/safener fb propanil/thiobencarb | 0.5 kg a.i./ha fb 1.2/2.4 kg a.i./ha | 1 fb 10 |
T4 | Pretilachlor/safener fb propanil/thiobencarb |
0.5 kg a.i./ha fb 1.2/2.4 kg a.i./ha |
1 fb 10 fb 30 |
T5 | Pretilachlor/safener fb propanil/thiobencarb fb MW | 0.5 kg a.i./ha fb 1.2/2.4 kg a.i./ha | 1 fb 10 fb 30 |
T6 | Propanil/thiobencarb | 1.2/2.4 kg a.i./ha | 10 |
T7 | Propanil/thiobencarb fb bentazon/MCPA | 1.2/2.4 kg a.i./ha fb. 0.6/0.1 kg a.i./ha | 10 fb 30 |
T8 | Propanil/thiobencarb fb MW | 1.2/2.4 kg a.i./ha | 10 fb 30 |
T9 | Cyhalofop-butyl + bensulfuron | 0.1 kg a.i./ha + 0.06 kg a.i/ha | 10 |
T10 | Cyhalofop-butyl + bensulfuron fb bentazon/MCPA | 0.1 kg a.i./ha + 0.06 kg a.i./ha fb 0.6/0.1 kg a.i./ha | 10 fb 30 |
T11 | Cyhalofop-butyl + bensulfuron fb MW | 0.1 kg a.i./ha + 0.06 kg a.i./ha | 10 fb 30 |
T12 | Bispyribac-sodium | 0.03 kg a.i./ha | 10 |
T13 | Bispyribac-sodium fb bentazon/MCPA | 0.03 kg a.i./ha fb 0.6/0.1 kg a.i./ha | 10 fb 30 |
T14 | Bispyribac-sodium fb MW | 0.03 kg a.i./ha | 10 fb 30 |
T15 | Season long weed-free | Season long | |
T16 | Season long weedy | — |
Different agronomic tools were integrated in this study to create a more competitive condition in favor of rice and hence to achieve higher weed control efficiency. Aerobic rice variety AERON 1 was used as the plant material, since it was the most competitive and productive weed under aerobic soil conditions as found in the previous study [
The soil was dry-ploughed and harrowed but not puddled during preparation. Rice seeds were directly dry-seeded at 2 cm depth in rows with 25 cm interrow and 15 cm intrarow spacing at the rate of 300 seeds/m2. Each plot, of size 5 m long and 3 m wide, was fertilized with triple super phosphate (TSP) and muriate of potash (MP) at the rate of 100 kg P/ha and 100 kg K/ha, respectively, during final land preparation; urea was top dressed thrice each at the rate of 50 kg N/ha at 2, 4, and 6 weeks after seeding. Soil was maintained under nonsaturated aerobic conditions throughout. The trial was primarily rain fed, but supplemental sprinkler irrigation was given when hair-like cracks appeared on the soil surface. Overflow canals were kept to facilitate drainage following heavy rainfall to avoid ponding. Different intercultural operations and plant protection measures were taken following standard practices [
A 25 cm × 25 cm quadrate was randomly placed lengthwise at four spots in each plot for recording of weed data at 10, 30, and 75 days after seeding (DAS). Weeds were clipped to ground level, identified and counted by species, and separately oven dried at 70°C for 72 h. Weed density (WD) and weed dry weight (WDW) were expressed as no./m2 and g/m2, respectively. Dominant weed species were identified using the summed dominance ratio (SDR) computed as follows [
Weed control rating was done visually at 7, 14, and 21 days after herbicide application (DAA) of each herbicide using a scale of 1 to 5 [
At maturity, yield attributes were recorded from ten randomly selected hills. All the panicles of sample hills were counted and converted to panicles/m2. Sample panicles were hand threshed; filled grains were separated from unfilled grains and counted to calculate filled grains/panicle. Central 3 m2 area of each plot was hand harvested to record grain yield (t/ha) and thousand-seed weight (g). Grain yield and thousand-seed weight were adjusted to 14% moisture content. Percent relative yield loss (RYL) due to weeds was calculated as [100 × (weed-free yield − weedy yield)/weed-free yield]. Crop phytotoxicity rating of different herbicides was assessed visually at 7, 14, and 21 days after application (DAA) of herbicide using a scale of 1 to 5 [
Economic analysis was performed following the procedure by Hussain et al. [
All data were subjected to ANOVA by using SAS statistical software package version 9.1 [
The study was conducted under naturally occurring mixed weed population. The experimental field was infested with broadleaf weeds, sedges, and grasses, and mostly dominated by broadleaf weeds. The weed community had a wide spectrum of 19 species representing 11 different families (Table
Weed composition with summed dominance ratio (SDR) followed by standard error (SE) in off season 2010 and main season 2010/2011 as observed in season-long weedy check.
Scientific name | Family name | SDR (SE) | |
---|---|---|---|
Main season |
Off season | ||
Broadleaves | |||
|
Solanaceae |
|
|
|
Scrophulariaceae |
|
|
|
Capparidaceae |
|
|
|
Onagraceae |
|
|
|
Euphorbiaceae |
|
|
|
Rubiaceae |
|
|
|
Fabaceae |
|
|
|
Amaranthaceae |
|
|
|
Euphorbiaceae |
|
|
|
Asteraceae |
|
|
Sedges | |||
|
Cyperaceae |
|
|
|
Cyperaceae |
|
|
|
Cyperaceae | — |
|
|
Cyperaceae |
|
|
Grasses | |||
|
Poaceae |
|
|
|
Poaceae |
|
|
|
Poaceae |
|
|
|
Poaceae |
|
— |
|
Poaceae |
|
|
Weed control was rated visually at 7, 14, and 21 DAA of herbicide (Table
Weed control rating and crop toxicity rating of different herbicides.
Herbicide | Weed control rating | Phytotoxicity rating | ||||
---|---|---|---|---|---|---|
Days after |
Days after | |||||
7 | 14 | 21 | 7 | 14 | 21 | |
Pretilachlor/safener | 1 | 2 | 3 | 2 | 1 | 1 |
Propanil/thiobencarb | 3 | 2 | 2 | 1 | 1 | 1 |
Cyhalofop-butyl + |
3 | 2 | 1 | 1 | 1 | 1 |
Bispyribac-sodium | 3 | 2 | 1 | 1 | 2 | 1 |
Bentazon/MCPA | 4 | 3 | 1 | 2 | 2 | 1 |
DAA: Days after application of herbicide; weed control rating: 1 = excellent/satisfactory, 2 = good, 3 = fair, 4 = poor, and 5 = no/very poor control; phytotoxicity rating: 1 = very slight injury, 2 = slight injury, 3 = phytotoxic, 4 = severely phytotoxic, and 5 = crop 100% killed.
Both weed dry weight and density were significantly influenced by weed control treatments at all the sampling dates (Table
Weed dry weight and weed density at different growth stages of rice variety AERON 1 as influenced by weed control treatments (averaged over seasons).
Treatment | Weed dry weight (g/m2) | Weed density (no./m2) | ||||
---|---|---|---|---|---|---|
10 DAS | 30 DAS | 75 DAS | 10 DAS | 30 DAS | 75 DAS | |
T1 | 2.25b | 61.18b,c | 52.89b,c | 56.48b | 122.74b,c | 124.89b,c |
T2 | 1.87b | 63.40b | 28.66e,f | 46.83b | 127.04b | 98.66e,f |
T3 | 2.43b | 10.17f,g | 39.68d,e | 60.77b | 20.38f | 109.68d,e |
T4 | 2.02b | 11.37f | 11.63g,j | 50.65b | 22.78f | 81.63g,h |
T5 | 1.80b | 12.22f | 6.77i,j | 44.93b | 24.41f | 76.77h |
T6 | 6.62a | 47.78d,e | 56.65b,c | 165.40a | 95.45d,e | 126.65b,c |
T7 | 6.53a | 44.59d,e | 21.87f,g | 163.18a | 89.01d,e | 91.87f,g |
T8 | 5.95a | 51.20c,d | 11.98g,j | 148.87a | 102.17d | 81.98g,h |
T9 | 5.92a | 38.73e | 48.72c,d | 148.05a | 77.34e | 118.72c,d |
T10 | 6.55a | 42.43de | 18.73f,i | 163.45a | 84.94d,e | 88.73f,h |
T11 | 6.42a | 44.43d,e | 7.87h,j | 160.68a | 88.94d,e | 77.87h |
T12 | 6.57a | 50.42d | 64.58b | 164.18a | 100.63d | 134.58b |
T13 | 5.93a | 52.53c,d | 19.37f,h | 148.25a | 104.80c,d | 89.38f,h |
T14 | 6.47a | 52.62c,d | 10.36g,j | 161.88a | 105.13c,d | 80.36g,h |
T15 | 0.00c | 00.00g | 00.00j | 00.00c | 00.00g | 00.00i |
T16 | 6.63a | 105.22a | 328.51a | 165.83a | 209.44a | 299.50a |
LSD | 0.74 | 10.37 | 12.59 | 18.36 | 20.19 | 13.05 |
T1: pretilachlor/safener fb bentazon/MCPA; T2: pretilachlor/safener fb manual weeding; T3: pretilachlor/safener fb propanil/thiobencarb; T4: pretilachlor/safener fb propanil/thiobencarb fb bentazon/MCPA; T5: pretilachlor/safener fb propanil/thiobencarb fb manual weeding; T6: propanil/thiobencarb; T7: propanil/thiobencarb fb bentazon/MCPA; T8: propanil/thiobencarb fb manual weeding; T9: cyhalofop-butyl + bensulfuron; T10: cyhalofop-butyl + bensulfuron fb bentazon/MCPA; T11: cyhalofop-butyl + bensulfuron fb manual weeding; T12: bispyribac-sodium; T13: bispyribac-sodium fb bentazon/MCPA; T14: bispyribac-sodium fb manual weeding; T15: season long weed-free by manual weeding; T16: season long weedy. LSD: least significant difference.
Within a column, means sharing same alphabets are not significantly different at
The WCE based on the weed dry weight at harvest varied significantly among the weed control treatments (Figure
Weed control efficiency of different weed control treatments in aerobic rice variety AERON 1 (averaged over seasons). T1: pretilachlor/safener fb bentazon/MCPA; T2: pretilachlor/safener fb manual weeding; T3: pretilachlor/safener fb propanil/thiobencarb; T4: pretilachlor/safener fb propanil/thiobencarb fb bentazon/MCPA; T5: pretilachlor/safener fb propanil/thiobencarb fb manual weeding; T6: propanil/thiobencarb; T7: propanil/thiobencarb fb bentazon/MCPA; T8: propanil/thiobencarb fb manual weeding; T9: cyhalofop-butyl + bensulfuron; T10: cyhalofop-butyl + bensulfuron fb bentazon/MCPA; T11: cyhalofop-butyl + bensulfuron fb manual weeding; T12: bispyribac-sodium; T13: bispyribac-sodium fb bentazon/MCPA; T14: bispyribac-sodium fb manual weeding; T15: season long weed-free by manual weeding; T16: season long weedy.
Grain yield of AERON 1 varied significantly due to weed control treatments (Table
Yield attributes, yield and relative yield loss of rice variety AERON 1 as influenced by weed control treatments (averaged over seasons).
Treatment | Panicles/ |
Filled grains/ |
Thousand-seed weight (g) | Grain yield (t/ha) | Relative yield loss (%) |
---|---|---|---|---|---|
T1 | 236.00e | 57.83e,f | 26.23e | 4.05e | 13.46 |
T2 | 235.17e | 59.00d,e | 26.28e | 4.13de | 11.75 |
T3 | 244.00d,e | 59.67c,e | 26.90d | 4.23c,e | 9.62 |
T4 | 270.83a | 63.90a,b | 27.33b,c | 4.49a,c | 4.06 |
T5 | 273.50a | 63.83a,b | 27.40a,b | 4.55a,b | 2.78 |
T6 | 220.83f | 54.17f,g | 26.05e | 3.67f | 21.58 |
T7 | 254.67c,d | 63.17a,c | 27.27b,c | 4.40a,d | 5.98 |
T8 | 258.00b,c | 62.17a,d | 27.33b,c | 4.43a,c | 5.34 |
T9 | 220.50f | 51.33g | 26.27e | 3.77f | 20.44 |
T10 | 268.50a,b | 64.12a,b | 27.32b,c | 4.47a,c | 4.49 |
T11 | 273.00a | 64.33a,b | 27.50a,b | 4.53a,b | 3.21 |
T12 | 215.83f | 53.83f,g | 26.27e | 3.60f | 23.08 |
T13 | 244.17d,e | 61.33b,e | 26.90d | 4.36b,d | 6.84 |
T14 | 271.17a | 64.50a,b | 27.32b,c | 4.45a,c | 4.91 |
T15 | 275.33a | 66.00a | 27.62a | 4.68a | 00.00 |
T16 | 180.43g | 45.83h | 25.53f | 1.77g | 62.18 |
LSD | 10.98 | 4.04 | 0.26 | 0.28 | — |
T1: pretilachlor/safener fb bentazon/MCPA; T2: pretilachlor/safener fb manual weeding; T3: pretilachlor/safener fb propanil/thiobencarb; T4: pretilachlor/safener fb propanil/thiobencarb fb bentazon/MCPA; T5: pretilachlor/safener fb propanil/thiobencarb fb manual weeding; T6: propanil/thiobencarb; T7: propanil/thiobencarb fb bentazon/MCPA; T8: propanil/thiobencarb fb manual weeding; T9: cyhalofop-butyl + bensulfuron; T10: cyhalofop-butyl + bensulfuron fb bentazon/MCPA; T11: cyhalofop-butyl + bensulfuron fb manual weeding; T12: bispyribac-sodium; T13: bispyribac-sodium fb bentazon/MCPA; T14: bispyribac-sodium fb manual weeding; T15: season long weed-free by manual weeding; T16: season long weedy. LSD: least significant difference.
Within a column, means sharing same alphabets are not significantly different at
Relative yield loss due to weed varied widely (2.78–23.081%) among the weed control treatments (Table
Weed control treatments showed a wide range of economic return (Table
Cost effectiveness of different herbicide treatments (averaged over seasons).
Ttreatment | Herbicide cost |
Laborer cost for spraying/ |
Total cost |
Gross income |
Net benefit |
---|---|---|---|---|---|
T1 |
|
|
277 | 4050 | 3773 |
T2 |
|
|
1417 | 4130 | 2713 |
T3 |
|
|
469 | 4230 | 3761 |
T4 |
|
|
579 | 4490 | 3911 |
T5 |
|
|
1719 | 4550 | 2831 |
T6 |
|
|
302 | 3670 | 3368 |
T7 |
|
|
412 | 4400 | 3988 |
T8 |
|
|
1552 | 4430 | 2878 |
T9 |
|
|
274 | 3770 | 3496 |
T10 |
|
|
384 | 4470 | 4086 |
T11 |
|
|
1524 | 4530 | 3006 |
T12 |
|
|
170 | 3600 | 3430 |
T13 |
|
|
280 | 4360 | 4080 |
T14 | 120 |
|
1420 | 4450 | 3030 |
T15 | 0.0 |
|
2500 | 4680 | 2180 |
T16 | 0.0 |
|
0.0 | 1770 | 1770 |
T1: pretilachlor/safener fb bentazon/MCPA; T2: pretilachlor/safener fb manual weeding; T3: pretilachlor/safener fb propanil/thiobencarb; T4: pretilachlor/safener fb propanil/thiobencarb fb bentazon/MCPA; T5: pretilachlor/safener fb propanil/thiobencarb fb manual weeding; T6: propanil/thiobencarb; T7: propanil/thiobencarb fb bentazon/MCPA; T8: propanil/thiobencarb fb manual weeding; T9: cyhalofop-butyl + bensulfuron; T10: cyhalofop-butyl + bensulfuron fb bentazon/MCPA; T11: cyhalofop-butyl + bensulfuron fb manual weeding; T12: bispyribac-sodium; T13: bispyribac-sodium fb bentazon/MCPA; T14: bispyribac-sodium fb manual weeding; T15: season long weed-free by Manual weeding; T16: season long weedy.
RM: Ringgit Malaysia. Market price of herbicide commercial products: pretilachlor/safener (Soffit N300 EC) = 70 RM/L, cyhalofop-butyl (Halop 100 EC) = 110 RM/L, bensulfuron (Tekong) = 19 RM 100/g, bispyribac-sodium (Nominee 100 SC) = 98 RM 250/mL, propanil/thiobencarb (Satuni) = 42 RM/L, and bentazon/MCPA (basagran M60) = 38 RM/L.
Manual weeding cost: 100 laborers/ha for 2 weedings at 25 RM/laborer/day, herbicide application cost: 2/laborer/ha/round at 25 RM/laborer/day, market price of paddy: 1000.00 RM t/ha, gross income = paddy yield (t/ha)
1 US$ = 3 RM (approx.).
The existence and risk of developing herbicide resistance and concern about herbicidal impact on environment and public health make herbicide dominated weed management increasingly vulnerable. To reduce herbicide reliance, one approach is to adjust crop management practices such that crop-weed interactions are altered to the benefit of the crop [
Naturally occurring weed flora of the study area represented 19 weed species belonging to 11 families. Broadleaf was the most dominant group followed by sedges and grasses. Weed community in the aerobic rice is generally dominated by broadleaf weeds followed by sedges and grasses [
Across the seasons, weed dry weight and density in the weedy check were recorded as 328 g/m2 and 299/m2, respectively. The high weed pressure under aerobic soil conditions as observed in this study is long established as reported by many researchers [
In this study, 14 different combinations of six commercial herbicide products were integrated with manual weeding aimed at controlling weeds during the predetermined critical period of weed competition of 20–43 days after seeding [
None of the herbicides under study caused any significant injury to rice plant, and thus, they exhibited high selectivity to rice. Minor injuries were evident with few herbicides which disappeared shortly. At the late season evaluation, no injury was visible from any herbicide treatment. As observed in the earlier study [
Weed control efficiency (WCE) was eventually translated into grain yield. All the weed control treatments significantly out-yielded weedy check, and some performed as good as weed-free check because of their high WCE. In contrast, weed control treatments with low WCE resulted in reduced yield. The WCE is also reflected in RYL. As evident from this study, the higher the WCE the lower the RYL. The increase in rice grain yield by increasing WCE has also been reported by others [
In the present study, all the yield attributes responded significantly to weed control treatments. These findings are in agreement with those of Sunil et al. [
The economics of a weed control method is determined by its cost involvement and WCE. Similarly as Wibawa et al. [
A more competitive cropping system in favor of rice as a consequence of combined use of competitive variety, higher seeding rate, and seed priming is evident from the study, which was reflected in lower weed pressure, higher weed control efficiency, and better yield. Weed control only during critical period of competition is also justified as some weed control treatments produced yield similar to weed-free yield. Herbicide and manual weeding combinations resulted in lower net benefit compared to herbicidal control because of high cost involvement in manual weeding. From economic view points, application of cyhalofop-butyl + bensulfuron or bispyribac-sodium or propanil/thiobencarb at 10 DAS followed by bentazon/MCPA at 30 DAS can be recommended, while for the sustainability of long-term weed management, cyhalofop-butyl + bensulfuron or bispyribac-sodium or propanil/thiobencarb should be applied in rotation at 10 DAS followed by a manual weeding at 30 DAS. Based on the findings of this study, an integrated weed management schedule for aerobic rice has been presented in Figure
Integrated weed management schedule for aerobic rice production.
The authors sincerely acknowledge UPM Research University Grant (01-04-08-0543RU) and Long term Research Grant Scheme (LRGS), Food Security Project, Ministry of Higher Education, Malaysia, for providing financial support of the project.