Weed-free Plots Research Articles

Impact of Nealley’s Sprangletop on Rough Rice Yield

AbstractTwo field studies were conducted in Louisiana to determine the impact of Nealley’s sprangletop on rough rice yield under multiple environments in 2014, 2015, and 2016. The first study evaluated optimal timings of Nealley’s sprangletop removal for optimizing rough rice yields. The second study evaluated the impact of Nealley’s sprangletop densities on rough rice yield. Nealley’s sprangletop was removed with applications of fenoxaprop at 122 g ai ha–1at 7, 14, 21, 28, 35, and 42 d after emergence (DAE). Nealley’s sprangletop removal at 7 and 14 DAE resulted in higher rough rice yields of 7,880 and 6,960 kg ha–1, respectively, when compared with the rice from the season-long Nealley’s sprangletop competition with a 6,040 kg ha-1yield. Delaying herbicide application from 7 DAE to 42 DAE resulted in a yield loss of 1,740 kg ha–1. Over the 35-d delay in application, rough rice yield loss from Nealley’s sprangletop interference was equivalent to 50 kg ha–1d–1. Nealley’s sprangletop densities were established at 1, 3, 7, 13, and 26 plants m–2by transplanting Nealley’s sprangletop when rice reached the one- to two-leaf stage. At Nealley’s sprangletop densities of 1 to 26 plants m–2, rough rice yields were reduced 10 to 270 kg ha–1, compared with the rice from weed-free plots. Based on regression analysis, Nealley’s sprangletop densities of 1, 35, 70, and 450 plants m–2reduced rough rice yield 0.14%, 5%, 10%, and 50%, respectively.

Competitive Ability of Santa-Maria (Parthenium hysterophorus L.) with Spring Maize

ABSTRACT: In recent decades, allelopathy has gained considerable attention in sustainable agricultural systems. In the current situation, an attempt has been made to investigate the optimal competition period for weed control in maize. Experiments were designed in randomized complete block design and Parthenium hysterophorus was naturally infested in experimental plots during the spring season 2014 to determine the critical competition period for weed control in maize. The relations between grain yield and different competition durations were determined via regression analyses. The experiment comprised seven treatments viz, control treatment, competition for 30, 45, 60, 75, 90 and 105 days after emergence. The results suggested that a weed-free period (control treatment) of maize was enough to provide acceptable grain yield. Whole season different competition periods and weed-free plots were included in the experiment for yield comparison. The highest grain yield was obtained from plot kept weed-free (control treatment). The results clearly indicated that P. hysterophorus was competitively more aggressive and its control in maize crop provide maximum grain yield.

Weed Management in Direct Seeded Rice Grown under Varying Tillage Systems and Alternate Water Regimes

ABSTRACT: In direct seeded rice (DSR), flushes of weeds are encountered, and mostly subsequent herbicides need to apply to control weeds that appear later. A farmer friendly approach was hypothesized in present study to integrate the management strategies for water, soil and cost effective weed free rice production. Efficacy of various herbicides in weed control to improve the performance of aerobic rice grown under varying tillage and alternate water regimes was evaluated. Five weed management techniques (weedy check, weed-free, pendimethalin followed by manual weeding, pendimethalin + bispyribac sodium (BS) + bensulfuron (B) and pendimethalin + MCPA) were carried out within the alternate wetting and drying (AWD) regimes (15 and 20 cm depth) under two tillage systems (zero and conventional). All the herbicide treatments reduced the weed intensity as compared to weedy check, however minimum weed density and dry biomass was observed in pendimethalin at 40 and 60 days after sowing, respectively. Under conventional tillage, weed free plots showed maximum leaf area index, leaf area duration and crop growth rate. Maximum plant height, 1000-kernel weight and kernel per panicle along with less percentage of abortive, chalky and opaque kernels were recorded in pendimethalin followed by BS+B as compared to weedy check plots. Among the herbicides application, pendimethalin followed by BS+B gave highest benefit to cost ratio and net benefits under both AWD regimes. Overall, application of pendimethalin followed by BS+B is an efficient and economic approach to reduce weed infestation which results in improved yield of aerobic rice.

Assessment of linseed (Linum usitatissimum L.) yield loss due to weed in Sinana, highland condition of Bale, South Eastern Ethiopia

Weed plays an important role in important role in proper stand establishment of the growing crops, which finally hinder productivity and quality of the crop . Field experimental was conducted at Sinana Agricultural Research Center on station during 2013-2015 growing season to determine optimum weeding frequency for weed management in linseed ( Linum usitatissimum L.). Weeding treatments consisted of five levels weedy check (no weeding), weeding at 30-35 days after emergency, weeding at 55-60 days after emergency, weeding at 30-35 and 55-60 days after emergency and total weed free . The results indicated that effects of weeding frequency observed on all yield parameter showed that the importance of weeding frequency for linseed growth, yield and yield component. However, significant (P≤0.05) effect of weeding frequency was not observed in the case of flowering date and plant height. The maximum seed yield was recorded from weed free plot (1808.35kg/ha) and weeding two times (30-35 and 55-60 days after crop emergence) (1621.58kg/ha) respectively. Weed significantly reduces the vegetative growth and productivity parameter of the crop. In this field trail 24.6% yield loss was observed in linseed when weeds are allowed to grow for the whole season. Weeding twice at 30-35 and 55-60 days after emergence was optimal for growth, yield and yield component of linseed. The major weed identified during the experimental conducted in the experimental site were Cyperus esculantus, Chenopodium album, Amaranthus spp. Guizotia scabra, Bromus pectinatus and Commelina benghlensisa.

Weed management in chickpea under irrigated conditions

In a study on chickpea at Uttar Pradesh, two hand weeding done in weedy check and weed free plot results indicated that weed control treatments significantly reduced the density of weeds. Maximum weed control efficiency (100%) was recorded with weed free plot. Among herbicides, maximum WCE (95.0%) was recorded in pre-emergence of pendimethalin1000 g/ha followed by combined PoE application of imazethapyr 75 g + quizalofop-ethyl 60 g/ha at 35 DAS and lowest WCE was recorded in weedy check. Among herbicides, the lowest number of plants (20.7/m2), plant height (33.4 cm) and number of pods/plant (22.4) at harvest stage of chickpea were recorded in PE application of pendimethalin 750 g/ha followed by combined PoE application of quizalofopethyl 60 g + oxyfluorfen 200 g/ha at 30 DAS. Maximum net monetary returns ` 53588/ha was recorded with pre-emergence application of pendimethalin 1000 g and PoE application of clodinafop 60 g/ha at 35 DAS.

The Importance of Planting Pot Marigolds (Calendula officinalis L.) in Degraded Public Spaces from the Agroecological and Economic Perspective

Summary The purpose of this paper is to analyse the introduction of certain plant species such as pot marigolds (Calendula officinalis L.) into neglected and predominantly urban spaces in the Republic of Serbia. The research was based on the results obtained in a two-year experiment conducted in the vicinity of the Novi Sad-Backa Palanka road. The primary objective of the experiment was to examine the behaviour of pot marigolds in poor-quality and neglected soils, with minimum cultural practices, in order to obtain novel plants in such adverse environments, which could be subsequently marketed in Serbia. The experiment commenced in 2014 by planting pot marigolds in plots previously cleared of weeds by mechanical tilling. In the spring of 2015, pot marigold seedlings, i.e. the first generation of plants obtained from the plots created in 2014, were planted in weed-free plots. The measurements were performed in three replicates from 10 October to 10 December 2015 in order to determine the number of volunteer plants, which could be further improved in nursery production and subsequently marketed in Serbia. The results obtained indubitably indicate that this and prospective studies exert positive ecological, agricultural and economic effects on a vast range of potential users.

Seeding rate and genotype effects on weeds and yield of dry-seeded rice

Weeds are the main biological constraint to wide spread adoption of dry-seeded rice (DSR). Research analyzing the effects of seeding rate on weeds and yield of DSR using newly developed genotypes adapted to DSR is not well documented in Asia. The objective of this study was to investigate the relative performance of selected genotypes in relation to seeding rate and weed infestation levels on weeds and yield of DSR in the rainy seasons of 2014 and 2015. Four selected genotypes [two cultivars (PR-115 and Dhan-202), and two recombinant inbred lines (RIL-367 and RIL-1646)], were grown in a split-split plot arrangement in a randomized complete block, with weed infestation levels (weed-free and partial weedy) in the main plots, seeding rate (100 and 200 seeds m−2) in the subplots, and genotypes in the sub-subplots. Total weed biomass was lower at the high seed rate (HSR; 200 seeds m−2) as compared to the low seeding rate (LSR; 100 seeds m−2), and the reduction in weed biomass varied from 40 to 72% depending on genotypes. At the LSR, the weed-competitive index (WCI) of RIL-1646 (1.13) was higher than PR-115 (0.44), but remained similar to RIL-367 and Dhan-202. At the HSR, the WCI of RIL-367 (1.57), RIL-1646 (2.24), and Dhan-202 (2.89) was higher than PR-115 (0.95). The WCI of newly developed genotypes (RIL-367, RIL-1646 and Dhan-202) increased with increased seeding rate, while for PR-115; no such increase was found. In the weed-free plots, RIL-367 at both the seeding rates had higher grain yield (5.97 t ha−1) than other genotypes and the lowest yield was recorded with Dhan-202, and the trend was similar at both the seeding rates. However, in the partial weedy plots, at both the seeding rates, the lowest yield was recorded for PR-115. In the partial weedy plots, the grain yield of RIL-367 was increased using the HSR. In the partial weedy plots, the plant height of RIL-367 at HSR was higher than that at LSR, and a similar trend was observed for panicle weight. There was a negative relationship between early plant height and relative grain yield loss due to weed infestation. This study indicates that the newly developed genotypes for DSR have variations in WCI, and weed control in DSR could be improved by increasing the seeding rate for these genotypes.

조 재배 시 피복비닐 제거시기에 따른 잡초발생과 조의 생육 및 수량 변화

조의 피복비닐의 적정 제거시기를 구명하고자 조 생육특성과 잡초방제에 미치는 효과는 다음과 같다. 표토관리별조의 초장은 파종 후 30일에 피복비닐을 한 관행구가 75.2 cm이었으며, 무처리구가 57.5 cm로 초기생육에서는 피복비닐 처리구가 초기 지온과 수분의 영향으로 양호하였다. 조의 출수기는 피복비닐을 제거한 구가 무처리구보다 2-3일 정도 빨랐다. 표토관리별 토양수분 함량은 파종 후 20일과 30일에 피복비닐을 제거한 구, 그리고 무처리구가 피복비닐을 제거하지 않은 파종 후 40일구와 대조구에 비해 높았다. 표토관리별 잡초발생량은 피복비닐을 파종 후 20일, 30일에 제거한 구에서 각각 86.5%, 84.0% 정도로 방제효과가 있었다. 수량은 파종 후 30일에 피복비닐을 제거한 구가 <TEX>$355kg\;10a^{-1}$</TEX>로 가장 높았고, 다음으로 파종 후 20일 순이었으며, 대조구는 도복에 의한 수량 감소로 <TEX>$275kg\;10a^{-1}$</TEX>이었다. 조재배 시 피복비닐의 제거시기는 파종 후 30일이 수량이 가장 높은 것으로 보아 가장 적절한 것으로 판단되었다. Weeding measures is an important issue for cereal crop because weed is superior to crops in early growth stage and there are not many herbicides applicable to cereal crop. Since the concern about well-being and eco-environmental products are increasing, cultivation with polyvinyl chloride (PVC) is needed. Five treatments included as weed-free, control (not remove weed) and covering with polyvinyl chloride removed 20, 30, 40 DAS (day after seeding). At removing PVC, plant height did not differ depending on the growth stage. However, weed-free plot by weed competition were somewhat short. And, removing PVC accelerated the earlier by 2-3 day than weed-free plot. Soil moisture which removed from the control was higher than 20, 30, 40 DAS and weed-free, and it was kept low by evaporation. The chlorophyll meter of weed-free plot was 34.3, 30 DAS was 40.6 at heading time. Weed-free showed that increased in weed population <TEX>$300.8g\;m^{-2}$</TEX>. Weed control value of 20 DAS, 30 DAS, 40 DAS were 86.5%, 84.0% and 74.8%, respectively. In 30 DAS, yield of foxtail millet according to treatment of removing PVC were <TEX>$355kg\;10a^{-1}$</TEX>. At weed competition early in 30 DAS, the removing PVC was good for control. Thus, 30 DAS was judged to be suitable.

Management of complex weeds in sugarcane by ametryn + trifloxysulfuron

Field experiment was conducted to evaluate the bio-efficacy of ametryn 73.15% + trifloxysulfuron 1.85% W.G for the management of grasses, sedge and broad-leaf weeds in sugarcane. The experiment consisted of nine treatments laid out in randomized block design with three replications. Cyperus rotundus, Ipomoea spp, Brachiaria reptans, Echinochloa colona, Digitaria sanguinalis and Dactyloctenium aegyptium were observed as major weeds. Among herbicide treatments, the lowest density of total weeds was observed with ametryn + trifloxysulfuron at 1500 g/ha though the differences were nonsignificant when compared with its lower dose i.e. 1250 g/ha at 15 and 45 days after application (DAA). Application of ametryn + trifloxysulfuron 1250 and 1500 g/ha recorded significantly lower weed dry weight over any other herbicidal treatment at 15 and 45 days. Highest weed control efficiency of total weeds at both 15 and 45 DAA were recorded with the application of ametryn + trifloxysulfuron 1500 g/ha which was closely followed by 1250 g/ha. The highest cane yields (9.04 t/ha and 10.51 t/ha) were recorded from weed free plot being at par with hand weeding thrice at 30, 60 and 90 DAP.

Effect of integrated weed management practices on weed biomass, yield and economics of okra(Abelmoschus esculentus)

A field experiment was conducted during rainy season of 2011 at Gwalior (Madhya Pradesh), India to study the effect of integrated weed management practices on growth, seed yield and economics of okra (Abelmoschusesculentus L. Moench) under the soil of sandy clay loam. In the experimental field Cyperus rotundus, Parthenium hysterophorus, Commelina benghalensis, Digera arvensis, Phyllanthus niruri and Cynodon dactyl on were found as dominant weed flora and contributes about 90% of the total weed flora. Minimum weed dry weight was recorded under two hand weeding (HW) at 15 and 30 days after sowing (DAS) at all the growth stages, followed by under grass mulch (5 t ha−1) one week after germination. Maximum number of weed population was recorded under weedy check. Weed control efficiency ranged from 63.93 to 97.67% at 60 DAS. The highest weed control efficiency was observed in two HW at 15 and 30 DAS (97.67%), followed by grass mulch 5 t ha −1 (97.56%), pendimethalin 1 kg ha −1 pre-emergence (PE) + one HW at 30 DAS (90.34%) and pendimethalin 1 kg ha−1 PE (89.47%). The highest seed yield and stalk yield of okra was recorded from the weed free plot (1102 and 6056 kg ha−1, respectively), which was on par with grass mulch5 tha−1 (1046 and 5935 kg ha). However benefit: cost ratio was higher (7.00) in grass mulch 5 t ha−1, followed by two HW at 15 and 30 DAS (6.47).

Effect of different herbicides on growth and yield attributes and seed cotton yield inhirsutumcotton

A field experiment was conducted during kharif seasons of 2012 and 2014 at C. S. Azad University of Agriculture & Technology, Kanpur to study the effect of different uses of herbicides on growth and yield attributes and seed cotton yield in hirsutum cotton. Data indicated that application of pendimethalin @ 1 kg a. i./ha as PE+quizalofopethyl @ 50 g a. i./ha 30 DAS+one hoeing 50 DAS and weed free plot improved significantly all the growth and yield attributing characters over weedy check. Weed free check plot produced significantly highest seed cotton yield (1311 kg/ha) and lint yield (442 kg/ha) than weedy check. Herbicidal application of pendimethalin @ 1 kg a. i./ha as PE+Quizalofopethyl @ 50 g a. i./ha 30 DAS+one hoeing 50 DAS was found next best treatment of producing significantly higher seed cotton yield (1157 kg/ha) and lint yield (357 kg/ha) than weedy check (514 kg/ha) and (174 kg/ha) seed cotton yield and lint yield, respectively. Lowest dry weight (3.98 g/m2) of weeds was recorded with direct spray of glyphosate 45% SL @ 1 kg a. i./ha. Higher weed control efficiency (83.3%) was recorded with direct spray of glyphosate 45% SL @ 1 kg a. i./ha followed by pendimethalin @ 1 kg a. i./ha as PE+quizalofopethyl @ 50 g a. i./ha 30 DAS+one hoeing 50 DAS (63.5%). Highest net returns (Rs. 19824/ha) and B: C ratio (1.56) were obtained with herbicidal application of pendimethalin @ 1 kg a. i./ha as PE+quizalofopethyl @ 50 g a. i./ha 30 DAS+one hoeing 50 DAS.

Efficacy of post- emergence application of Imazethapyr in summer mungbean (&lt;italic&gt;Vigna radiata&lt;/italic&gt; L.)

Imazethapyr is a now emerging post-emergence (PoE) herbicide for pulses. A field experiment was conducted for two consecutive years (2011-12) to assess the efficacy of imazethapyr in summer mungbean (&lt;italic&gt;Vigna radiate&lt;/italic&gt; L.) in a mild alkaline soil of Kanpur, India. Treatment comprised of five different doses of Imazethapyr [0 (Weedy check), 40, 60, 80, 100 g ha-1] along with weed free treatment. Results revealed that summer mungbean yield was reduced up to 38.6% due to weeds infestation. Post-emergence application of imazethapyr significantly reduced the (P£0.05) weed population and weed biomass and the herbicide effectiveness was increased up to the dose of @ 80 g/ha. The relative suppression effect of imazethapyr was in the order of grassy weed&gt;Sedges&gt;broad-leaf weeds. However, the study suggest that the dose of 100 g/ha is needed for suppressing the &lt;italic&gt;Cyperus spp&lt;/italic&gt;. to a significant extent. The weed control efficiency (WCE) of imazethayr was more than 40 per cent at a dose of 100 g/ha and the corresponding value of weed control index (WCI) was more than 60 per cent. The highest average grain yield of summer mungbean was recorded in weed free plot (926 g/ha) which was on a par with imazethapyr @ 100 g/ha (920 kg/ha) and imazethapyr @ 80 g/ha (883 kg/ha). The increase yield under imazethapyr treated plots was mainly due to the increase in plant biomass, nodule number, root weight, number of seed per plant and number of pod per plant. Although, the net return was highest under imazethapyr @ 100 g/ha (Rs. 24, 880/ha) the marginal rate of return was higher in imazethapyr @ 80 g/ha (627%).

Efficacy and economics of different herbicides, their weed species selectivity, and the productivity of mechanized dry-seeded rice

A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI) farm in Los Baños, Philippines, to evaluate the economic performance of PRE oxadiazon and pendimethalin, early POST butachlor plus propanil and thiobencarb plus 2,4-D, and late POST herbicides bispyribac-sodium and fenoxaprop plus ethoxysulfuron applied solely or sequentially. All herbicide treatments with PRE or early POST herbicides reduced total weed density by 85–100% and biomass by 80–100%, whereas late POST treatments reduced weed density by 32–50% and biomass by 40–62% compared with the nontreated weedy check. The highest grain yield was achieved in weed-free plots (5.9–6.1 t ha−1) and the lowest in weedy plots (0.2 t ha−1). Among the herbicide treatments, rice treated with oxadiazon, thiobencarb plus 2,4-D, and butachlor plus propanil followed by the late POST herbicides had grain yield increments of 23–25, 20 to 26, and 18 to 23 times that of the yield in weedy plots, respectively. The economic analysis showed that the sole application of oxadiazon provided the highest net profit and benefit-cost ratio in both years, which was similar to the treatments involving oxadiazon or early POST herbicides, followed by the sequential application of late POST herbicides.

Yield Losses in Chickpea with Varying Densities of Dragon Spurge (Euphorbia dracunculoides)

Knowledge of economic threshold level and growth habits of weeds in chickpea is essential to implement timely, effective, and economical weed control treatments. The effect of weed density on growth and yield performance in chickpea using dragon spurge as a test weed was investigated for 2 consecutive yr. Dragon spurge density levels of 5, 10, 15, 20, 25, 30, 35, and 40 plants m−2 were compared with weed-free plots. Each increment in densities of dragon spurge from 5 to 40 plants m−2 reduced plant height, number of fruits, seeds, and dry weight per plant. Chickpea grain yield losses varied between 1 to 63% with dragon spurge density ranging from 5 to 40 plants m−2. The seed protein content of chickpea was found to be significantly reduced above a weed density of 25 plants m−2. Maximum N, P and K uptake by dragon spurge was 1,520, 1,020, and 7,350 mg m−2, respectively. Thus, dragon spurge should be controlled at densities above 5 plants m−2 to achieve optimum chickpea yield.

Weed dynamics as influenced by tillage system, sowing time and weed competition duration in dry-seeded rice

Cultural practices alter patterns of crop growth and can modify dynamics of weed-crop competition, and hence need to be investigated to evolve sustainable weed management in dry-seeded rice (DSR). Studies on weed dynamics in DSR sown at different times under two tillage systems were conducted at the Agronomic Research Farm, University of Agriculture, Faisalabad, Pakistan. A commonly grown fine rice cultivar ‛Super Basmati’ was sown on 15th June and 7th July of 2010 and 2011 under zero-till (ZT) and conventional tillage (CONT) and it was subjected to different durations of weed competition [10, 20, 30, 40, and 50 days after sowing (DAS) and season-long competition]. Weed-free plots were maintained under each tillage system and sowing time for comparison. Grassy weeds were higher under ZT while CONT had higher relative proportion of broad-leaved weeds in terms of density and biomass. Density of sedges was higher by 175% in the crop sown on the 7th July than on the 15th June. Delaying sowing time of DSR from mid June to the first week of July reduced weed density by 69 and 43% but their biomass remained unaffected. Tillage systems had no effect on total weed biomass. Plots subjected to season-long weed competition had mostly grasses while broad-leaved weeds were not observed at harvest. In the second year of study, dominance of grassy weeds was increased under both tillage systems and sowing times. Significantly less biomass (48%) of grassy weeds was observed under CONT than ZT in 2010; however, during 2011, this effect was non-significant. Trianthema portulacastrum and Dactyloctenium aegyptium were the dominant broad-leaved and grassy weeds, respectively. Cyperus rotundus was the dominant sedge weed, especially in the crop sown on the 7th July. Relative yield loss (RYL) ranged from 3 to 13% and 7 to 16% when weeds were allowed to compete only for 20 DAS. Under season-long weed competition, RYL ranged from 68 to 77% in 2010 and 74 to 80% in 2011. The sowing time of 15th June was effective in minimizing weed proliferation and rectifying yield penalty associated with the 7th July sowing. The results suggest that DSR in Pakistan should preferably be sown on 15th June under CONT systems and weeds must be controlled before 20 DAS to avoid yield losses. Successful adoption of DSR at growers' fields in Pakistan will depend on whether growers can control weeds and prevent shifts in weed population from intractable weeds to more difficult-to-control weeds as a consequence of DSR adoption.

Effect of crop establishment methods and weed control treatments on weed management, and rice yield

Lower water availability coupled with labor shortage has resulted in the increasing inability of growers to cultivate puddled transplanted rice (PTR). A field study was conducted in the wet season of 2012 and dry season of 2013 to evaluate the performance of five rice establishment methods and four weed control treatments on weed management, and rice yield. Grass weeds were higher in dry-seeded rice (DSR) as compared to PTR and nonpuddled transplanted rice (NPTR). The highest total weed density (225–256plantsm−2) and total weed biomass (315–501gm−2) were recorded in DSR while the lowest (102–129plantsm−2 and 75–387gm−2) in PTR. Compared with the weedy plots, the treatment pretilachlor followed by fenoxaprop plus ethoxysulfuron plus 2,4-D provided excellent weed control. This treatment, however, had a poor performance in NPTR. In both seasons, herbicide efficacy was better in DSR and wet-seeded rice. PTR and DSR produced the maximum rice grain yields. The weed-free plots and herbicide treatments produced 84–614% and 58–504% higher rice grain yield, respectively, than the weedy plots in 2012, and a similar trend was observed in 2013.

Weed management inrabionion (Allium cepaL.)

A field experiment was carried out during rabi season of 2012-13 at Junagadh to find out practically convenient and economically feasible weed management practice in onion. The experiment comprised of ten treatments of pre-emergence and post- emergence herbicides, their combination with hand weeding, weed free and unweeded control. The experiment was laid out in randomized complete block design with three replications. Weed free check treatment (three hand weeding at 15, 30, 45 and 60 DAT) recorded significantly the lowest dry matter of weeds and the highest weed control efficiency. All the growth and yield attributes of onion viz., plant height (58.87 cm), no. of leaves (15.11), neck thickness (1.4 cm), A grade bulb (42.60 %), fresh bulb weight (70 g), bulb diameter (5.75 cm) and bulb yield (40.9 t ha-1) were recorded maximum in weed free plots. This treatment also recorded minimum bolters (0.0 %) and doubles (1.12 %), the highest gross ( 3,27,200 ha-1) & net return ( 2,87,471) and maximum B:C ratio (7.12). However, treatment combined spray of oxyfluorfen @ 0.240 kg ha-1 and propaquizafop @ 0.090 kg ha-1 as PE followed by second spray as POE at 45 DAT was equally effective with this treatment.

The critical period for weed control in dry-seeded rice

The critical crop-weed competition period in a dry-seeded rice system is an important consideration in formulating weed management strategies. Field experiments were conducted in the summer seasons of 2012 and 2013 at the Punjab Agricultural University, Ludhiana, India, to determine the extent of yield loss in two different rice cultivars (PR 114 and PR 115) with different periods of weed interference. Twelve weed control timings were used to identify critical periods of weed competition in dry-seeded rice. PR 114, a long-duration rice cultivar (145 d) having slower initial growth than PR 115 (125 d), was more prone to yield losses. In both years, 100% yield loss was observed where weeds were not controlled throughout the season. In weed-free plots, the grain yield of PR 114 was 6.39–6.80 t ha−1, for PR 115, it was 6.49–6.87 t ha−1. Gompertz and logistic equations fitted to yield data in response to increasing periods of weed control and weed interference showed that, PR 114 had longer critical periods than PR 115. Critical weed-free periods to achieve 95% of weed-free yield for PR 114 was longer than for PR 115 by 31 days in 2012 and 26 days in 2013. Weed infestation also influenced the duration of critical periods. Higher weed pressure in 2012 than in 2013 increased the duration of the critical period of crop-weed competition in that year. The identification of critical crop-weed competition periods for different cultivars will facilitate improved decision-making regarding the timing of weed control and the adoption of cultivars having high weed-suppressing abilities. This will also contribute to the development of integrated weed management in dry-seeded rice systems.

Influence of Integrated Weed Management Practices on Dynamics and Weed Control Efficiency in Dry Direct Seeded Rice

Field experiment under dry direct seeded rice(Oryza sativa L.) was conducted during rainy season of 2010 and 2011 at Regional Agriculture Research Station (RARS), Parwanipur, Bara to develop appropriate weed management practices for dry direct- seeded rice. The trial was laid-out in randomized complete block design (RCBD) and replicated thrice. Observations were taken on weed, plant growth and yield attributing, yield, and socio-economic parameters. The weed density, dry weed weight and weed control efficiency resulted significantly different as influenced by integrated weed management practices. Low weed population density, low weed index and highest weed control efficiency resulted by pendimethalin followed by 2, 4- D followed by one hand weeding were at par with weed free check. Highest yield resulted from weed free plot followed by pendimethalin followed by two hand weeding and pendimethalin followed by 2, 4- D followed by one hand weeding. However, the net return per unit investment resulted highest in pendimethalin followed by 2, 4- D followed by one hand weeding. This proved that amid increasing wage rate and labour scarcity integrated weed management through pendimethalin 30 EC (Stomp) @1 kg a. i. /ha as pre- emergence herbicide application followed by 2, 4- D sodium salt 80 WP @ 0.5 kg a. i. /ha followed by one hand weeding or stale seed bed followed by pendimethalin 30 EC (Stomp) @1 kg a. i. /ha followed by bispyribac (Nominee gold) @25 g a. i. /ha 10% @200 ml/ha at 20 days of seeding resulted best alternative for manual hand weeding practices giving higher net return per unit investment. DOI: http://dx.doi.org/10.3126/njst.v14i2.10413 Nepal Journal of Science and Technology Vol. 14, No. 2 (2013) 33-42

Competitive ability of Australian canola (Brassica napus) genotypes for weed management

Canola (Brassica napus L.) is an important break crop in Australian cropping systems but weeds are a major cost to production and herbicide-resistant weeds are spreading. The potential competitive ability of canola genotypes to both suppress weed growth and maintain grain yield and quality in the presence of weeds has not been determined in Australia. Two experiments examined the range in competitive ability of 16 B. napus genotypes against annual ryegrass (Lolium rigidum Gaud.) and volunteer wheat (Triticum aestivum L.) over two contrasting seasons. Weed biomass at flowering was generally reduced 50% more in the presence of the strongly competitive genotypes than the least competitive, and this has significant benefits for lower weed seed production and reduced seedbank replenishment. Suppression of weed growth was negatively correlated with crop biomass. Significant differences in grain yield of canola were recorded between weedy and weed-free plots, depending on crop genotype, presence of weeds and season. Crop yield tolerance (where 0% = no tolerance and 100% = complete tolerance) to ryegrass competition ranged from 0% (e.g. with CB-Argyle) to 30–40% (e.g. with the hybrids 46Y78 and Hyola-50) in the dry season of 2009. Yield tolerance was higher (50–100%) with the lower densities of volunteer wheat and in the 2010 season. The range between genotypes was similar for both conditions. The hybrids and AV-Garnet were higher yielding and more competitive than the triazine-tolerant cultivars. The ranking of genotypes for competitiveness was strongly influenced by seasonal conditions; some genotypes were consistently more competitive than others. Competitive crops are a low-cost tactic for integrated weed management to reduce dependence on herbicides and retard the spread of herbicide-resistant weeds.