Weed Management In Direct-seeded Rice Research Articles

Performance of Post-Emergence Herbicide Combinations on Weed Management and Crop Yield in Direct Seeded Rice (Oryza sativa L.)

Direct-seeded rice (DSR), an innovative alternative to traditional transplanting, has gained popularity for its cost-effectiveness and labour-saving attributes. Weeds pose a significant threat to DSR. In this study, the effectiveness of various weed management methods, including hand weeding and herbicide applications, was evaluated. Hand weeding proved most effective in controlling weeds, while specific herbicides, such as bispyribac sodium + pyrazosulfuron (T2) and triafamone + ethoxysulfuron (T6) applied at 16 days after sowing (DAS), demonstrated superior weed control efficiency, improved growth parameters, and enhanced yield. Paspalum distichum was effectively controlled by penoxsulam + cyhalofop-butyl (T7). The study emphasizes the importance of customizing weed control to local conditions, with the choice of suitable herbicides and practices aligning with prevalent weed biotypes in the specific farming system. Understanding the nuanced impacts of post-emergence herbicides is crucial in navigating the intricate landscape of weed management in direct-seeded rice.

Effect of nitrogen levels and weed management on weed flora and yield of direct-seeded rice (Oryza sativa) in southern part of Punjab

An experiment was conducted at Krishi Vigyan Kendra, Ferozepur, Punjab during rainy (kharif) seasons of 2018 and 2019 to study the effects of nitrogen levels and weed management in direct-seeded rice (Oryza sativa L.) (DSR). The results indicated that pendimethalin + bispyribac (W1) (5.25 and 2.95 m2) and oxadiargyl + bispyribac (W2) (6.05 and 3.95 m2) application reduced the density of narrow-leaved weeds (NLW) and broad-leaf weeds (BLW) followed by oxadiargyl + fenoxaprop (W3) (7.0 and 4.55 m2) during both the years. Application of W1 decreased the total weed biomass by 84–98.2%, respectively compared to weedy check (W5) (80.1 and 94.8 g/m2) in both years. Treatment W1 and W2 recorded at par values of grain and straw yield followed by W3. An increase (48.6–72.0%) in grain yield was registered with weed practices compared to weedy check in DSR. W1 and W2 significantly recorded higher N uptake in grain (61.45 and 60.85 kg/ha) and total (100.8 and 99.45 kg/ha) followed by W3 (53.85 and 90.35 kg/ha, respectively). The high infestation of BLW with W3 resulted in the lowest weed control efficiency (WCE) (46.2–53.9%) among the weed control practices. N at 120 and 150 kg/ha recorded the low density and biomass of NLW and BLW. Application of 120 and 150 kg N/ha enhanced the grain yield (4.89 and 5.25 t/ha) and net returns (55.1 and 60.5 × 103 ₹/ha) in both years. No N application recorded lowest N uptake in grain (87.71 kg/ha) and total (80.26 kg/ha) compared to 150 kg N/ha in both years. N levels at 120 and 150 kg/ha recorded higher values of water control efficiency (WCE). Based on the findings, it may be concluded that pendimethalin + bispyribac and oxadiargyl + bispyribac with N 120 kg/ha application can reduce weed flora diversity with higher grain yield of direct-seeded rice in Punjab.

UAV-based Herbicide Application for Efficient Weed Management in Direct-seeded Rice

Background: Weeds are the key pest, which reduce crop productivity. Direct-seeded rice is very prone to early-stage weed infestation during initial crop development. Cultural and mechanical methods are difficult due to unavailability of labour and poor work efficiency. Hence, use of herbicides is an effective method for timely weed control. However, the efficacy of agrochemicals depends on the efficiency of spraying equipment. Conventional knapsack sprayers are used most often to spray herbicides but they are highly time-consuming, labour intensive and labour drudgery practices. Hence, the current experiment was aimed to study the efficiency of unmanned aerial vehicles (UAVs) on weed management. Methods: A field experiment was conducted at Tamil Nadu Agricultural University, Coimbatore during summer, 2022 to evaluate the efficacy of UAV-based herbicide application in direct-seeded rice. The study comprised of five weed management treatments such as pre emergence application of pretilachlor with safener and pyrazosulfuron through both UAV and knapsack sprayer and unweeded check as control. The experimental plot was laid out in a randomized block design with four replications. Result: The experimental findings showed that the application of pre-emergence pretilachlor significantly reduced the density and dry weight of grasses, sedges and broad leaved weeds in knapsack application. Moreover, it was found on par with UAV application of same herbicide without any phytotoxicity to rice seedlings. From the experiment, the application of pre-emergence pretilachlor through UAV is found to be more effective for timely weed control during early stages in direct-seeded rice, which reduce the labour intensity and drudgery than knapsack application.

Evaluation of pre-emergence herbicides for weed management and rice yield in direct-seeded rice in Cambodian lowland ecosystems

Poor weed management in direct-seeded rice (DSR) at crop establishment stage has led to the need to explore different pre-emergence herbicides to reduce weed biomass and increase DSR yield in Cambodian lowland ecosystems. This study evaluated weed and yield responses to pre-emergence herbicides (pendimethalin, pretilachlor, butachlor, oxadiazon and no application as the control) under different weed management options during the 2018 and 2019 early wet seasons in farmers’ rice fields. All pre-emergence herbicides reduced weed flora and pendimethalin was most effective in controlling the population of mainly grassy weeds. Pendimethalin significantly reduced weed dry biomass by 36.2% (21.3 ​g ​m−2) in 2018 compared with the untreated control. In 2019, weed dry biomass was significantly reduced by 46% (17.9 ​g ​m−2) with butachlor compared with the untreated plot. Pendimethalin increased toxicity in rice plants, which decreased SPAD (leaf greenness) by 44.8% and tiller numbers by 39.3% at 7 days after herbicide application (DAPH) compared with butachlor, but plants recovered from pendimethalin toxicity at 14 DAPH. In 2018, oxadiazon herbicide significantly increased grain yield by 61% (4.6 ​t ​ha −1) compared with the untreated control, but oxadiazon produced similar grain yields as pendimethalin. In 2019, there was no significant effect of pre-emergence herbicides on yield but butachlor produced the highest rice yield (3.2 ​t ​ha−1) followed by pendimethalin (2.8 ​t ​ha−1) and oxadiazon (2.7 ​t ​ha−1). Our study demonstrated that pre-emergent herbicides function differently under varying soil-water conditions in 2018 and 2019, therefore rice growers can use butachlor to control weeds in dryer soil conditions and potentially use pendimethalin to control weeds in good soil moisture conditions. This information is crucial and safe in developing appropriate strategies to manage weeds and enhancing DSR productivity in lowland ecosystems.

Understanding Strategic Weed Management in Direct Seeded Rice - A Review

Transplanting in puddled soils (intensive tillage in ponded conditions) with continuous flooding is the most common method of rice crop establishment in Asia. However, the most important problem associated with transplanted rice is that change in soil aggregates and development of hardpan below the soil surface caused due to flooding and puddling, which is not desirable for following wheat crop. Although, this is advantageous for effective weed control in the transplanted rice field. The technique of flooding the field with water is not only very laborious, tidy, and cumbersome but also very expensive, and time-consuming. The direct seeding of rice seems to be the only viable alternative to liberate farmers. However, weeds are the main biological constraint in DSR. Weed problems associated with DSR (direct seeded rice) have been explained in this review paper and also the strategies to develop for weed management in DSR. In this effort the chapter has been covered by elaborating the techniques of prevention, land preparation, effect of sowing time on weed dynamics, impact of planting density on weed dynamics, impact of row spacing, mechanical weed control, nutrient management, water management, chemical weed control and integrated weed management in context to DSR with a view to achieve enhanced rice yield similar to that under transplant condition.

Weed competitive cultivars as a component of integrated weed management in direct-seeded rice: A Review

Weed competitive cultivars as a component of integrated weed management in direct-seeded rice: A Review

Impacts of conservation agriculture and herbicides on weeds, nematodes, herbicide residue and productivity in direct-seeded rice

The transplanted puddled rice (TPR) followed by (∼fb) conventional till wheat (CTW) system (TPR-CTW) in the Indo-Gangetic Plains (IGP) of India is the most remunerative cropping system, serving as the backbone of food security of India. Its sustainability, however, is threatened due to degradation/ scarcity of resources (soil, water, fuel/energy, labour), low inputs-use efficiencies, insurgence/resistance of new weeds/pests, and high pesticides use, and greenhouse gases (GHGs) emissions and global warming. Direct-seeded rice (DSR) can save resources, improve soil conditions, reduce GHGs emissions, and can reverse the declining trends. The performance of DSR, however, is largely influenced by weeds and nematodes. Therefore, this experiment was undertaken to evaluate the impacts of conservation agriculture (CA)-inclusive DSR, supplemented with herbicides/weed control measures on weeds, nematodes, and rice productivity and profitability. Results showed that the DSR fb ZTW had 82 % higher weed densities at 45 days after sowing (DAS) than TPR-CTW. The DSR fb ZTW, and DSR + brown manuring (BM) fb ZTW systems resulted in significantly higher parasitic nematodes, namely, Tylenchorhynchus brevilineatus Williams, Meloidogyne graminicola Golden & Birchfield, Pratylenchus thornei Sher & Allen than TPR-CTW. The CA-based triple cropping system with residue [∼DSR with mungbean residue (MR) fb ZTW with rice residue (RR) fb ZT mungbean (ZTMB) with wheat residue (WR)] led to considerable reduction of these nematodes. It gave similar rice yield with TPR-ZTW and TPR-CTW, and 40–43 % higher yield than DSR-ZTW. Pendimethalin 1.5 kg ha−1 at pre-emergence fb bispyribac-Na 25 g ha-1 at post-emergence and hand weeding (HW) at 35 DAS offered better weed control, higher rice yield (by 123–130 %), net returns (by 327–806 %) and net benefit:cost. The above CA-based triple cropping system with pendimethalin + bispyribac + HW would lead to an effective weed management in DSR without the risk of residual toxicities of pendimethalin and bispyribac-Na to crops grown in sequence. This can serve as an alternative to TPR in the Indian IGP, and in similar agro-ecologies. Controlling weeds using these herbicides may suppress nematodes and reduce the cost of nematodes control.

Weed management approaches in direct-seeded rice in eastern Indian ecologies - A critical and updated review

Direct-seeded rice (DSR) is significant in modern day agriculture because it requires less water input (20%) and labour (65–80 person-days/ha). Moreover, it enables farmers to establish rice early, which allows the crop stand more power to resist flush flood happening more frequently in the beginning of the monsoon. Direct-seeded rice produces at par or higher yield compared to manual transplanted rice but significantly higher yield (1.07 t/ha) compared to traditional manual broadcasted rice followed by beushening practice. It helps to increase system productivity by 0.25 t/ha, increase income by US$ 150/ha, reduce greenhouse gas emission (20% GWP) besides instrumental in reducing straw burning and environmental footprints. Despite all these advantages, the DSR has not been adopted at large scale at farmers’ field in eastern India particularly in Bihar, Odisha and Uttar Pradesh. One of the most important reasons for this is heavy and diversified weed infestation in DSR which consequently reduces rice yields significantly. In the present review article, the authors have tried to compile relevant information on the weed management approaches in DSR with special reference to eastern Indian states. Detailed discussions on weed species based on their occurrence and infestation, critical period of weed competition and different methods of weed management in DSR in eastern Indian ecologies have been enlightened in this paper. It also includes that weed management options in DSR depend on many factors like land situation, soil condition, water status, planting geometry and resources availability; and therefore, one single method of weed management practices may not be sufficient to control all the flushes of diversified weeds. Integrated approach combining cultural, physical and chemical methods can provide a more robust control of weeds in DSR. Relevant data generated in Odisha representing eastern Indian ecologies have also been included herein to further enrich knowledge and skills regarding DSR productivity, in general and possible weed management options, in particular.

Integrated weed management in direct-seeded rice: dynamics and economics

Weeds are often the most severe problem in direct-seeded rice (Oryza sativa L.) (DSR), causes reductions in yield and profitability. The traditional method of controlling rice weeds or manual weeding has several demerits as the practice is uneconomical and difficult. The effects of 10 different weed management practices were evaluated to identify the most effective and economical methods of managing weeds in DSR during in Nepal during the rainy season of 2010. Pendimethalin was applied pre-emergence where 2,4-D, bispyribac sodium, and oxadiargyl were applied post-emergence alone or combined with hand weeding. Sesbania (Sesbania aculeata Wild. Pers.) was co-cultured with rice and killed by 2,4-D. Weed emergence, density, and biomass per unit area of 3 weed types: broadleaf, sedges, and grasses were assessed during 20, 40, 60 days after seeding (DAS), and at harvest. Treatments were compared either to weedy check or weed-free control to determine weed control indices. A total of 42 weed species belonging to 27 genera and 11 families emerged across the growing season of rice. Most of the weeds were annual where broadleaf and sedges were dominant during the first two months, and grasses were dominant under flooding. Weeds reduced the rice yield by more than 80% in weedy-check with respect to weed-free control. A sequential application of pendimethalin as pre-emergence and bispyribac-sodium postemergence herbicides followed by a hand weeding at 45 DAS provided up to 85% weed control over weedy check than other weed control measures. However, that method found uneconomical when compared to the same without hand weeding because of the high cost of manual labor. Pendimethalin was effective in controlling early flush of weeds and bispyribac efficiently controlled weeds even after flooding turned out to be a less expensive method controlling in DSR. An integrated approach of weed management including both pre-emergence and post-emergence herbicides can provide season-long weed control greater economic return.

Effects of nitrogen levels and weed management in direct-seeded rice

A field experiment was conducted at Agricultural Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi to study effect of nitrogen level and weed management in direct-seeded rice. Treatment consisted of 12 treatment combinations which was laid out in the split-plot design having nitrogen levels (100, 120, 140 and 160 kg N/ha) in main plot and three weed management practices, viz. weedy, two hand weeding and bispyribac-sodium 25g/ha fb Cono-weeding in sub-plots replicated thrice. Two hand weeding recorded significantly lower weed biomass and density and better performance of crop growth and yield attributes and yield followed by bispyribac-Na 25 g/ha fb cono-weeding. In case of nitrogen application of 160 kg N/ha showed better performance of growth, yield attributes and yield as compared to other nitrogen treatments. It was observed that application of nitrogen 160 kg/ha and two hand weeding was found best treatment for higher grain yield and net returns.

Integrated weed management in direct-seeded rice

A field investigation was conducted during Kharif season of 2014 and 2015 at Varanasi, Uttar Pradesh, to study the effect of integrated weed management on weed flora, yield and economics of direct seeded rice (Oryza sativa L.). Penoxsulam 35 g/ha at 10 DAS fb 1 hand weeding at 35 DAS reduced weed density of various weed flora, viz. Echinocloa colona (7.27%), Echinocloa crus-galli (6.58%), Cynodon dactylon (7.57%) among grasses; Cyperus iria (8.01%), Cyperus difformis (8.26%) and Fimbristylis miliacea (8.67%) among sedges and Ammannia baccifera (10.12%) and Caesulia axillaris (10.10%) among broad-leaved weeds besides other weeds (11.72%) in comparison to penoxsulam 35 g/ha at 20 DAS fb 1 hand weeding at 35 DAS. Penoxsulam 35 g/ha at 10 DAS fb 1 hand weeding at 35 DAS markedly improved growth attributes, viz. plant height, number of tillers/m2, dry matter accumulation, leaf area index and chlorophyll content at 60 DAS and yield attributes, viz. panicle length, panicle weight, number of panicles/m2, number of grains/panicle and test weight. Penoxsulam 35 g/ha at 10 DAS fb 1 hand weeding at 35 DAS statistically influenced the grain and straw yields and harvest index over all other treatments except hand weeding at 15 and 35 DAS. Highest net return (43790.76) and benefit: cost ratio (2.15) was also observed under penoxsulam 35 g/ha at 10 DAS fb1 HW at 35 DAS.

Assessment of post-emergence weed management in direct-seeded rice

The present study was carried out at G.B. Pant University of Agriculture and Technology, Pantnagar during rainy seasons 2014 and 2015 to determine the efficacy of post-emergence application of cyhalofop-butyl in managing weeds in direct-seeded rice. Eight treatments, viz. cyhalofop-butyl 10% EC at 65, 75, 80 and 90 g/ha, cyhalofop-butyl 10% EC at 75 and 80 g/ha, hand weeding twice at 20 and 40 DAS and untreated control were laid out in a randomized block design with three replications. Application of cyhalofop-butyl controlled grassy weeds better than the non-grassy weeds and recorded maximum weed control efficiency, higher yield attributes and yield. Application of cyhalofop-butyl in rice did not show any phytotoxic effect on succeeding wheat.

Herbicide combinations for weed management in direct-seeded rice

Ten treatments were evaluated during Kharif 2013, 2014 and 2015 at Palampur (Himachal Pradesh) to study their impacts on weeds, crop and economics. Echinochloa colona was the most competitive weed followed by Aeschynomene indica and Panicum dichotomiflorum. Oxadiargyl fb bispyribac, pyrazosulfuron fb bispyribac, pendimethalin fb bispyribac fb manual weeding and bispyribac + chlorimuron + metsulfuron-methyl gave significantly lower count of E. colona and Panicum dichotomiflorum. The economic threshold levels (no/m2) with the weed management practices studied varied between 2.5–17.8/m2. With every 1 weed/m2 increase in density, the grain yield of dry-seeded rice was reduce by 62.4 kg/ha. Manual weeding engaged more labour and had higher cost tending to increase the economic threshold over herbicidal treatments. Cost of weed control under herbicidal/integrated treatments was 14–49% of weed free and 19.9–69.3% of that under mechanical weeding. Oxadiargyl fb bispyribac resulted in highest net return due to weed control. Crop resistance index and efficiency index were highest and weed index was minimum under pendimethalin fb bispyribac fb manual weeding. Weed management index, agronomic management index and integrated weed management index were highest under pendimethalin fb manual weeding followed by bispyribac, pendimethalin fb bispyribac and mechanical weeding. The overall performance index (OPi) was highest under pendimethalin fb bispyribac fb manual weeding (1.34) followed by oxadiargyl fb bispyribac (1.31), pyrazosulfuron fb bispyribac (1.18), bispyriac + chlorimuron + metsulfuron (1.14) and bisppyribac (1.12). Weeds reduced the grain yield of rice by 67.1%.

A new herbicide mixture: bispyribac sodium+metamifop 14% SE for weed control in wet seeded rice

In direct seeded rice (DSR), weeds are the major biotic constraint in improving the productivity of rice. Acute labour shortage and hike in wage rate force the farmers to rely more on herbicides for weed management in DSR. But the continuous use of same herbicide or herbicides with similar mode of action leads to shift in weed flora and resistance development in weeds. One of the ways to overcome these problems is the use of herbicide mixtures. Hence, field experiments were conducted for two seasons kharif 2014 and rabi 2014–15 to assess the bio-efficacy of bispyribac sodium+metamifop, a post-emergence herbicide mixture for broad spectrum weed control in DSR. The experiment was laid out in randomized block design with seven treatments and three replications. The treatments comprised four doses of bispyribac sodium+metamifop viz., 60, 70, 80 and 90 g/ha, bispyribac sodium @ 25 g/ha, hand weeding twice and weedy check.Schoenoplectus juncoides, Cyperus iria, Cyperus difformis, Fimbristylis miliacea, Isachne miliacea, Ludwigia perennis, Limnocharis flava, Sphenoclea zeylanica, Marsilea quadrifolia, Bergia capensis, Commelina diffussa and Monochoria vaginalis were the major weeds in the experimental field. Among the three morphological groups of weeds, sedges was the most predominant one in the experimental site. Results revealed that compared to bispyribac sodium @ 25 g/ha, bispyribac sodium+metamifop @ 70, 80 and 90 g/ha was found more effective in reducing the density and dry weight of weeds. Application of bispyribac sodium+metamifop @ 90 g/ha registered the highest weed control efficiency of 96.62%. Grain yield was also significantly influenced by the weed control treatments. The highest grain yield (8051 kg/ha) and net returns (Rs. 86238/ha) were recorded in bispyribac sodium+metamifop @ 90 g/ha and it was statistically comparable with the lower doses of 80 and 70 g/ha. Bispyribac sodium+metamifop @ 90, 80 and 70 g/ha was significantly superior to hand weeding twice and bispyribac sodium applied @ 25 g/ha in terms of net returns and B: C ratio.

Effect of nitrogen scheduling and weed management on weed density, growth and yield of direct-seeded rice (Oryza sativaL.)

A field experiment was conducted during rainy (kharif) seasons of 2012 and 2013 to study the effect of nitrogen scheduling and weed management in direct-seeded rice (Oryza sativa L.) under irrigated condition. Nitrogen scheduling significantly reduced the total weed density and dry weight and increased the yield-attributing charactersand yield of crop. The results indicated that the minimum total weed density and dry weight, and maximum crop growth and yield attributing characters were recorded under four nitrogen splits: ¼ 2 WS+¼ 4 WS+¼ 6 WS+¼ 8 WS followed by 1/3 2 WS+1/3 4 WS+1/3 6 WS. Application of nitrogen scheduling at ¼ basal+¾ 4 WS and ¼ basal+½ 4 WS+¼ 6 WS recorded higher weed density and dry weightat all stages of observation during both the years. The various weed management treatments significantly decreased the density and dry weight of weed and increased the weed control efficiency, growth and yield attributing characters compared with the weedy check. Application of pendimethalin 1.0 kg/hafb bispyribac+carfentrazone (25 + 20 g)/ha and pendimethalin 1.0 kg/ha fb bispyribac+ethoxysulfuron (25+18 g)/ha recorded minimum weed density and dry weight of weed and increased the weed control efficiency, growth and yield attributing characters comparable to other treatments.

Effect of post–emergence application of cyhalofop-butyl for weed management in direct-seeded rice (Oryza sativa)

A field experiment was conducted during rainy season of 2009 at the research farm of the Indian Agricultural Research Institute, New Delhi to evaluate the appropriate combination of pre-emergence and post-emergence herbicides in direct-seeded rice (Oryza sativa L.). All the weed control treatments brought significant increase in grain (25-52%) and straw yield (27-58%) as compared to season long crop weed competition. Cyhalofop-butyl residues in soil were found below detectable level indicating safety to soil microbial population and succeeding crop. It may be concluded that weeds can be managed during critical period of competition with the sequential application of pretilachlor (750 g/ha) as pre-emergence followed by post- emergence application of cyhalofop-butyl (60 g/ha) at 30 DAS in direct-seeded rice.

Seed Germination Ecology of Echinochloa glabrescens and Its Implication for Management in Rice (Oryza sativa L.)

Echinochloa glabrescens is a C4 grass weed that is very competitive with rice when left uncontrolled. The competitive ability of weeds is intensified in direct-seeded rice production systems. A better understanding is needed of factors affecting weed seed germination, which can be used as a component of integrated weed management in direct-seeded rice. This study was conducted to determine the effects of temperature, light, salt and osmotic stress, burial depth, crop residue, time and depth of flooding, and herbicide application on the emergence, survival, and growth of two populations [Nueva Ecija (NE) and Los Baños (IR)] of E. glabrescens. Seeds from both populations germinated at all temperatures. The NE population had a higher germination rate (88%) from light stimulation than did the IR population (34%). The salt concentration and osmotic potential required to inhibit 50% of germination were 313 mM and −0.24 MPa, respectively, for the NE population and 254 mM and −0.33 MPa, respectively, for the IR population. Emergence in the NE population was totally inhibited at 4-cm burial depth in the soil, whereas that of the IR population was inhibited at 8 cm. Compared with zero residue, the addition of 5 t ha−1 of rice residue reduced emergence in the NE and IR populations by 38% and 9%, respectively. Early flooding (within 2 days after sowing) at 2-cm depth reduced shoot growth by 50% compared with non-flooded conditions. Pretilachlor applied at 0.075 kg ai ha−1 followed by shallow flooding (2-cm depth) reduced seedling emergence by 94−96% compared with the nontreated flooded treatment. Application of postemergence herbicides at 4-leaf stage provided 85−100% control in both populations. Results suggest that integration of different strategies may enable sustainable management of this weed and of weeds with similar germination responses.

Ecological studies on Echinochloa crus-galli and the implications for weed management in direct-seeded rice

Echinochloa crus-galli, a C 4 grass, is one of the world’s most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8 cm. A burial depth of only 0.4 cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6 ton ha −1) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.

Multiple herbicide resistance in barnyardgrass (Echinochloa crus-galli) in direct-seeded rice in the Philippines

Barnyardgrass (Echinochloa crus-galli [L.] Beauv.), a troublesome weed in rice production, has been confirmed for the first time to be resistant to both chloroacetamide (butachlor)- and acetanilide (propanil)-group herbicides commonly used in direct-seeded rice in the Philippines. Resistance screening showed that 17 of 18 sampled populations (94%) were resistant to butachlor + propanil. Dose–response assays using butachlor + propanil on the populations resulted in all but one not being controlled at twice the recommended rate for field application (1.4 kg ai or 2 l/ha) and seven populations not being controlled by 4 l/ha (2.8 kg ai). Dose–response assays using butachlor and propanil separately indicated that the latter populations were resistant to both of the herbicides. LD50 values for butachlor + propanil populations ranged from 0.6 l/ha (0.42 kg ai) to 2.9 l/ha (2.03 kg ai) indicating 1.9 to 9.1 times less sensitivity than a known susceptible population. Thus, what was perceived by farmers to be reduced herbicide efficacy is actually herbicide resistance. Hence, this new development in major herbicides has become a threat in rice production and will alter weed management in direct-seeded rice. Concerted efforts in raising awareness on herbicide resistance and implementing an effective integrated weed management program are needed.

Effect of nitrogen and weed management in direct-seeded rice (Oryza sativa) under upland conditions

A field experiment was conducted during the rainy season of 2002 and 2003 at Sabour study the effect of nitro- gen and weed management in direct-seeded upland rice (Oryza sativa L.). Grain and straw yields of rice and N, P and K uptake by rice crop and weeds increased significantly with successive increase in nitrogen up to 120 kglha. The splits in which basal application of nitrogen was skipped off resulted in significantly higher yield attributes, grain and straw yields and nutrient uptake by crop in comparison to splits wherein part of nitrogen was applied at sowing owing to lower weed dry weight and nutrient depletion by weeds that resulted in higher weed-control effi- ciency and N-use efficiency. Among the weed-management practices, 2 hand-weedings at 20 and 40 days after sowing and pre-emergence application of butachlor at 1.5 kglha + 1 hand-weeding at 30 DAS were at par; they significantly reduced the density and dry weight of weeds and nutrient depletion by weeds. These treatments sig- nificantly increased the nutrient uptake by the crop, resulting in higher grain yield (4.18 and 4.16 tlha) of 120 kg N/ ha as a result of higher weed-control efficiency (90.6 and 84.3%), N-use efficiency (33.5 and 32.9 kg grainlkg of N applied) and production efficiency (60.4 and 60.3 kg grainlkg N applied) respectively. However, minimum nutrient uptake by crop and miximum nutrient removal by weeds were noted under weedy check.