Rice Weeds Research Articles

Herbicide use history and weed management in Southeast Asia

Southeast Asia’s rich natural resources and favorable climatic conditions make it conducive for intensive rice-based, corn-based and perennial crops-based cropping systems. Regardless of the cropping system, weeds remain to be among the major factors that limit yields. The use of herbicides to manage weeds in these systems has been increasing through the years. The use of 2,4-D started in the late 1940s and remains as a major herbicide to control rice weeds. The 1980s saw the introduction of multiple [...]

Influence of Rice Herbicides on Weed Growth and Nutrient Removal under Different Tillage in Rice–Yellow Sarson Cropping Sequence

A field experiment was conducted during June–February, 2019–20 and 2020–21 to evaluate the impact of tillage and rice herbicides on weed growth, nutrient removal by weeds and the productivity of residual yellow sarson under rice–yellow sarson cropping. Two tillage system viz. zero tillage (ZT–ZT) and conventional tillage (CT–CT) in main plot and six herbicide combinations [oxadiargyl at 90 g ha-1 followed by (fb) bispyribac-sodium at 25 g ha-1, penoxsulam+cyhalofop-butyl at 180 g ha-1, oxadiargyl at 90 g ha-1 fb penoxsulam+cyhalofop-butyl at 180 g ha-1, fenoxaprop-p-ethyl+ethoxysulfuron at 90+15 g ha-1, oxadiargyl at 90 g ha-1 fb fenoxaprop-p-ethyl+ethoxysulfuron at 90+15 g ha-1 and pendimethalin at 1000 g ha-1 fb bispyribac-sodium at 25 g ha-1] along with unweeded and weed free check were assigned in sub plot in rice. Under ZT–ZT, the nutrient removal by weeds was found to be less, while, yellow sarson removed (uptake) greater amount of nutrients besides producing better growth attributes and yield as compared to those under CT–CT. Zero tillage (ZT–ZT) recorded 37.0 and 37.3% higher seed and stick yield of yellow sarson as compared to CT–CT. The herbicides applied in rice had no carryover effect on the growth and yield of the yellow sarson. However, oxadiargyl fb fenoxaprop-p-ethyl+ethoxysulfuron and oxadiargyl fb penoxsulam+cyhalofop-butyl were found to be better to control weeds in rice (92-95% Weed control efficiency) compared to other herbicide combinations (21–91%). Hence, the ZT–ZT system with oxadiargyl at 90 g ha-1 fb fenoxaprop-p-ethyl+ethoxysulfuron at 90+15 g ha-1 and oxadiargyl at 90 g ha-1 fb penoxsulam+cyhalofop-butyl at 180 g ha-1 appeared to be the best option for managing weeds, reducing nutrient loss and obtaining higher yield of yellow sarson under rice–yellow sarson sequence.

Characterization of lodging variation of weedy rice.

Weedy rice (Oryza spp.), one of the most notorious weeds of cultivated rice, evades eradication through stem lodging and seed shattering. Many studies have focused on seed shattering, whereas variations in lodging have received less attention and the underlying mechanisms that cause the differences in lodging between weedy and cultivated rice have not been studied in detail. Here, we compared lodging variation among diverse Chinese weedy rice strains and between weedy rice and co-occurring cultivated rice. The chemical composition of basal stems was determined, and transcriptome and methylome sequencing were used to assess the variation in expression of lodging-related genes. The results showed that the degree of lodging varied between indica-derived weed strains with high lodging levels, which occurred predominantly in southern China, and japonica-derived strains with lower lodging levels, which were found primarily in the north. The more lodging-prone indica weedy rice had a smaller bending stress and lower lignin content than non-lodging accessions. In comparison to co-occurring cultivated rice, there was a lower ratio of cellulose to lignin content in the lodging-prone weedy rice. Variation in DNA methylation of lignin synthesis-related OsSWN1, OsMYBX9, OsPAL1, and Os4CL3 mediated the differences in their expression levels and affected the ratio of cellulose to lignin content. Taken together, our results show that DNA methylation in lignin-related genes regulates variations in stem strength and lodging in weedy rice, and between weed strains and co-occurring cultivated rice.

Protective enzyme activity regulation in cotton (Gossypium hirsutum L.) in response to Scirpus planiculmis stress.

Scirpus planiculmis, an important weed in rice and cotton fields, stresses crop growth and development, leading to yield loss. However, it is unclear how stressed plants respond to this weed. In this study, we analysed the stress effect of S. planiculmis on cotton under different weed densities, competition periods, and distribution conditions from the perspective of morphogenesis, physiological metabolism and crop yield. The effect of a low dose of herbicide on the relationship between cotton and S. planiculmis was also explored. The results showed that plant height, stem diameter, fresh weight, root length, boll number, single boll weight and yield of cotton all decreased with increasing S. planiculmis density and damage. The spatial distribution of S. planiculmis had no significant effect on plant height, stem diameter, fresh weight or root length of cotton, but crop yield loss decreased with increasing distance. S. planiculmis stress altered cotton chlorophyll, soluble protein and malondialdehyde (MDA) content, and protective enzyme activities. Compared with superoxide dismutase (SOD) and peroxidase (POD) activities, catalase (CAT) activity was increased under different S. planiculmis stress conditions. Therefore, we concluded that CAT plays a key role in protecting enzymes involved in defence responses. Under low-dose herbicide action, the activities of protective enzymes were increased, which helped cotton plants to resist S. planiculmis stress. The results revealed that regulating protective enzyme activities is important in cotton responses to S. planiculmis stress.

Novel RNA Viruses Discovered in Weeds in Rice Fields.

Weeds often grow alongside crop plants. In addition to competing with crops for nutrients, water and space, weeds host insect vectors or act as reservoirs for viral diversity. However, little is known about viruses infecting rice weeds. In this work, we used metatranscriptomic deep sequencing to identify RNA viruses from 29 weed samples representing 23 weed species. A total of 224 RNA viruses were identified: 39 newly identified viruses are sufficiently divergent to comprise new families and genera. The newly identified RNA viruses clustered within 18 viral families. Of the identified viruses, 196 are positive-sense single-stranded RNA viruses, 24 are negative-sense single-stranded RNA viruses and 4 are double-stranded RNA viruses. We found that some novel RNA viruses clustered within the families or genera of several plant virus species and have the potential to infect plants. Collectively, these results expand our understanding of viral diversity in rice weeds. Our work will contribute to developing effective strategies with which to manage the spread and epidemiology of plant viruses.

Green water-dispersible coarse powder nano-formulation for allelopathic leaf extract of Mikania micrantha Kunth ex H.B.K. in controlling the rice weed Echinochloa colona (L.) Link

Plant extracts originated from an exotic species, Mikania micrantha Kunth ex H.B.K. have shown appreciable phytoinhibitory activities against a rice weed, Echinocloa colona (L.) Link. In spite of that, the glutinous extracts exhibit poor physicochemical properties preventing it from delivering efficiently and for ease of application. This research study aimed to formulate the leaf extract of M. micrantha with pre-emulsions and lignocellulosic coarse powder for the sake of ameliorated bioefficacy of the extract via nano-delivery system and improved product handling. Three pre-emulsions were developed using rapeseed oil methyl esters (ROME) and disparate bisurfactant mixtures including polyalkoxylated fatty alcohol (PAFA)-alkyl sulfonate (AS), PAFA-cocamidopropyl betaine (CB) and PAFA-alkyl polyglucosides (APG). The pre-emulsions were incorporated with leaf extracts containing the phenolic allelochemicals. The pre-emulsified extracts were loaded onto mercerized lignocellulose by solvent percolation and evaporation (SPE) technique produced the formulated water-dispersible coarse powders, WDP-F1, WDP-F2 and WDP-F3. A non-formulated extract was prepared into water-dispersible powder, WDP-EX for quality control. The results show greater water absorption by the formulated powders in prolonged duration of 7 days exerted the release of higher total amount of phenolic compounds (63.66–86.52%) than the phenolics amount released from the non-formulated powder (41.98%). Transmission electron microscopy (TEM) revealed the formulated extracts exhibited particles release in regular patterns from three dimensional networks and gigantic vesicles, unlike the non-formulated extract liberated uneven particles from disordered aggregates. The particles released from the formulated powders displayed low mean sizes (87.56–103.27 nm) in monodisperse range (PDI = 0.180–0.203). In opposition, non-formulated particles indicated larger mean size (423.93 nm) and polydisperse (PDI = 0.550). In the glasshouse study, the formulated powders promoted significantly higher inhibitions of germination, shoot height, fresh weight and dry weight of E. colona than non-formulated powder and non-treated weedy control. Moreover, the paddy seedling growth and grain yield treated with the formulated powders were statistically equivalent (p = 0.05) to treated with a commercial formulation, Satunil® and weed-free non-treated control. These valuable outcomes genuinely reflected the inspirational use of green water-dispersible coarse powder in the formulation of natural products in fostering the sustainable development of crop protection products.

Predictive Modelling for Rice Weeds in Climate Change: A Review

Rice (Oryza sativa L.) is an important staple food not only for Asians but also for people worldwide. However, weeds in rice fields can cause yield reduction due to their tendency to compete for resources. These significant biological obstacles can potentially cause complete yield loss if inappropriately managed. In addition, future climate change can cause rice weeds to become more competitive against cultivated rice plants by providing new favourable conditions for the unwanted species to expand aggressively. As the effect of climate change on rice weeds has been studied, the abiotic parameters, including carbon dioxide concentration, atmospheric temperature, drought, and soil salinity, can be used to construct predictive modelling to forecast rice weed infestation. If the weed invasion in rice fields can be predicted accurately based on the weather information, the farmers can prepare the countermeasure early to avoid high yield loss. However, some challenges need to be faced by the researchers as the weed invasion depends not only on the climate condition alone. This review summarizes the effect of climatic variation on weed infestation in rice fields. It also discusses how predictive modelling can be developed based on the information of the environmental conditions and their challenges.

Allelopathic Potential of Mangroves from the Red River Estuary against the Rice Weed Echinochloa crus-galli and Variation in Their Leaf Metabolome.

Mangroves are the only forests located at the sea–land interface in tropical and subtropical regions. They are key elements of tropical coastal ecosystems, providing numerous ecosystem services. Among them is the production of specialized metabolites by mangroves and their potential use in agriculture to limit weed growth in cultures. We explored the in vitro allelopathic potential of eight mangrove species’ aqueous leaf extracts (Avicennia marina, Kandelia obovata, Bruguiera gymnorhiza, Sonneratia apetala, Sonneratia caseolaris, Aegiceras corniculatum, Lumnitzera racemosa and Rhizophora stylosa) on the germination and growth of Echinochloa crus-galli, a weed species associated with rice, Oryza sativa. Leaf methanolic extracts of mangrove species were also studied via UHPLC-ESI/qToF to compare their metabolite fingerprints. Our results highlight that A. corniculatum and S. apetala negatively affected E. crus-galli development with a stimulating effect or no effect on O. sativa. Phytochemical investigations of A. corniculatum allowed us to putatively annotate three flavonoids and two saponins. For S. apetala, three flavonoids, a tannin and two unusual sulfated ellagic acid derivatives were found. Some of these compounds are described for the first time in these species. Overall, A. corniculatum and S. apetala leaves are proposed as promising natural alternatives against E. crus-galli and should be further assessed under field conditions.

Weed management in rainfed lowland rice ecology in Nigeria – challenges and opportunities

AbstractDeveloping an effective weed management strategy is crucial to sustainable rice production in Nigeria. Rainfed lowland ecology contributes significantly to the volume of rice cultivated in terms of yield and land acreage. Nevertheless, increased weed infestation remains one of the major production constraints. This review highlights the strength and weaknesses of weed management practices in rainfed lowland ecology and research gaps, and examines the potential for developing a sustainable weed management strategy for lowland rice. In this review, a rainfed lowland situation is described (where water is limited) to engage flooding as a potential weed control option, due to the undulating land terrains. Effective weed management begins with creating a weed-free environment at the critical crop growth stages, such that broadcasted or transplanted rice seedlings can efficiently use water, nutrients, and light. Sustainable weed management practices in Nigerian lowland ecology would therefore imply that farmers begin to incorporate crop rotation to suppress problem weeds in continuous rice cropping systems; adopt conventional or minimum tillage to enhance herbicide efficacy and early establishment of rice; adopt weed-competitive and high-yielding cultivars; and practice appropriate spacing, seeding rate, and seeding methods that can support easy adoption of mechanical weeders and optimum plant population to suppress weed pressure at a later growth stage. This is feasible where farmers are supported with infrastructure, farm machinery, and other necessary inputs. Future research should engage lowland rice farmers in specific agroecological zones.

Multiple compensatory mutations contribute to the de‐domestication of Iberian weedy rice

Societal Impact StatementWeedy plants are a major constraint on agricultural productivity. Weedy rice is a weed that invades rice fields worldwide and is responsible for reductions in rice yields. Studies to date have detected multiple independent weedy rice origins in different parts of the world. We investigated the origin of weedy rice in Spain and Portugal and found that it has evolved from a cultivated rice variety group grown locally. Iberian weeds carry mutations that reverse domesticated pericarp color to its ancestral red color. Our results imply that management strategies are needed to prevent the evolution of troublesome weeds from cultivated ancestors.Summary Weedy rice, a damaging conspecific weed of cultivated rice, has arisen multiple times independently around the world. Understanding all weedy rice origins is necessary to create more effective weed management strategies. The origins of weedy rice in Spain and Portugal, where there are no native Oryza species, are unknown. In this study, we try to identify the likely ancestors of Iberian weedy rice and the mechanisms involved in the evolution of two weedy traits, seed shattering, and red pericarps. We used genotyping by sequencing to understand the origin of Iberian weedy rice and its relationship to other weedy, wild, and cultivated rice groups worldwide. We also genotyped candidate genes for shattering and pericarp color. We find that weedy rice in the Iberian Peninsula has primarily evolved through de‐domestication of temperate japonica cultivars, with minor origins from exotic weedy rice. Iberian weeds have evolved the capacity to shatter seeds via novel loci and have acquired red pericarps via compensatory mutations in the Rc domestication gene. Our results suggest the Iberian weeds have experienced selection at multiple locations in the genome to establish as weeds, likely targeting male fertility genes among other functions. Our characterization of Iberian weedy rice adds to the growing evidence that de‐domestication of cultivated rice varieties is the main source of weedy rice worldwide. Their evolutionary versatility explains why weedy rice continues to be one of the most problematic weeds of cultivated rice.

Impact of temperature and soil moisture on paddy weed and productivity: A case of Lalitpur District, Nepal

Rice (Oryza sativa L.) is a major food crop for around 60% of the global population. The production of rice has been challenged by various biotic and abiotic factors. Temperature and soil moisture are the major abiotic and weeds are the major biotic factors for yield loss. The present experiment was conducted to investigate the impact of temperature and soil moisture on rice weed and rice productivity. The experiment was carried out under different temperatures (ambient, ambient +2°C, and ambient +3°C) and soil moisture (ambient, 25-30%, and 10-15%) conditions for the entire crop growth period from June to October 2014. Rice weeds were recorded after 28, 47 and 93 days of rice transplantation for varied soil moisture. Similarly, at varied temperature weeds were recorded after 19, 44 and 66 days of rice transplantation. The results showed that weed density increases under elevated temperature at 2°C and 3°C than under an ambient condition (existing in the surrounding area). An experiment on soil moisture stress indicates a reduction in rice productivity as the density of weed increases with the deficiency of soil moisture. Further studies on temperature and soil moisture resisting rice variety are essential. This study suggests that research on the control of weed species, targeting those weeds benefited at elevated temperature and soil moisture stress conditions, is necessary.

Distribution and resistance of barnyardgrass to quinclorac in rice fields in Thailand

Background: In Thailand, Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass) is the most problematic weed in rice. Quinclorac was first commercialized in 1997 in Thailand and became the primary herbicide option for barnyardgrass control. The intensive use of quinclorac in rice fields increases the risk of the evolution of resistant barnyardgrass. Objective: This study was conducted to survey the occurrence of quinclorac-resistant barnyardgrass in Thailand, investigate the levels of quinclorac resistance, and evaluate alternative control measures for quinclorac-resistant barnyardgrass. Methods: [...]

Salinity effects on rice, rice weeds, and strategies to secure crop productivity and effective weed control. A review

Salinity effects on rice, rice weeds, and strategies to secure crop productivity and effective weed control. A review

Performance Comparison of the Implementations of Single Row Power Weeder (Single Engine) and Multi-Row Power Weeder (Twin-Engine) in Rice Fields

Weeding rice weeds is done to reduce and prevent the competition of nutrients absorption between weeds/grass and rice plants. Weed control can be applied through various techniques, including pulling and piling the weeds into the soil. Weeds buried in the soil can be decomposed and become nutrients for rice plants. One application of technology used in weeding weeds is the use of single row power weeder (single engine) and multi-row power weeder (twin-engine). The research aimed to compare the performance of using a single row power weeder (single engine) and a multi-row power weeder (twin-engine) in rice fields. The multi-row power weeder was designed by combining a single row power weeder. This research was conducted by testing the performance of the power weeder in rice fields in an area of 14 m x 4 m for each replication. The total area of land used was 560 m2 with five experimental replicates. Weeding activities were carried out on rice plants aged 30 DAP. The results showed a successive comparison between the performance of the single row power weeder (single engine) and the multi-row power weeder (twin-engine), such as the theoretical working capacity was 0.037 ha/hour and 0.054 ha/hour, effective working capacity was 11.11 minutes and 9.78 minutes, the efficiency of the weeder performance was 82.48% and 64.87%, fuel consumption was 1.07 liters/hour and 1.92 liters/hour, and the success rate of weeding was 64.41 % and 59.77 %. The calculation results of the plant damage levels were 15 plants and 31 plants, while the mudding index values were 75.26% and 77.62%. The results of this study showed that the advantages of using a single row power weeder were on the parameters of effective working capacity, weeding efficiency, fuel, weeding success, and low plant damage. The advantages of the multi-row power weeder were the parameters of theoretical working capacity, effective working capacity, and muddling index.

Screening of Herbicides for Rice Seedling Safety and Echinochloa colona Management under Australian Conditions

Different herbicides are currently required for sustainable weed management in aerobic rice. Three pot experiments were conducted using different herbicides to evaluate rice safety and for the control of Echinochloa colona, a major weed of aerobic rice. Among the pre-emergence (PRE) herbicides, it was found that pendimethalin (594 g ai ha−1) and flumioxazin (60 g ai ha−1) were relatively safe herbicides for rice and provided 100% control of E. colona. All other PRE herbicides, such as atrazine, cinmethylin, clomazone, dimethenamid-P, isoxaflutole, metribuzin, prosulfocarb + S-metolachlor, pyroxasulfone, trifluralin, and S-metolachlor reduced the biomass of rice compared with the non-treated control. Dose-response studies revealed that flumioxazin and pendimethalin even at low doses (30 g ai ha−1 for flumioxazin and 294 g ai ha−1 for pendimethalin) provided excellent control (>95%) of E. colona. Post-emergence (POST) application of paraquat (360 g ai ha−1) at the time of rice emergence caused toxicity in the crop, but also provided excellent control of E. colona. When applied just after crop emergence (11 days after sowing), Pendimethalin was found to be safe for rice (2% mortality) and reduced the biomass of E. colona by 88% compared with the non-treated control. It is quite possible that the rice variety Reiziq used in this study may have a tolerance to flumioxazin, which needs further investigation involving more rice varieties. This study suggests that flumioxazin can be used as an alternative to pendimethalin for the sustainable management of E. colona in aerobic rice.

Taxonomy of the weed species of the genus Echinochloa (Poaceae, Paniceae) in Southwestern Europe: Exploring the confused current state of affairs.

The taxonomy of Echinochloa, a predominantly tropical to warm-temperate genus of 40-50 species, including some of the world's worst weeds, is still poorly understood. This is because some species, including the extremely widespread E.crus-galli, show a wide range of morphological, physiological and ecological variation, in part the result of a complex recent evolutionary history. Furthermore, there is often a dearth of clear distinguishing features among species. The same applies to the species established in Southwestern Europe, where unintentionally introduced populations have now established themselves as important weeds of crops, especially maize and rice. Taxonomic and nomenclatural confusion hampers progress in weed science. In this study, we give an identification key that covers the weedy taxa encountered in Southwestern Europe, followed by notes on taxonomy and nomenclature. Moreover, a lectotype is designated for Echinochloafrumentacea. It is argued that current confusion cannot be overcome without including populations of Eastern Asian origin in taxonomic studies and without the joint efforts of experts in the fields of weed science, morphology-based taxonomy, genomics and phylogenetics.

Weed communities in the irrigated rice paddies of northern Iran

Dedicated insights into the diversity, spatial and temporal distribution of rice weed communities, as well as underlying ecological factors, are critical for developing effective ecological weed management strategies in these agroecosystems, leading to the preservation of biodiversity and ecosystem services in a sustainable agriculture framework. To fulfill this aim, 108 vegetation relevés were conducted at 23 sites of rice paddies throughout 9 counties in the north of Iran at various altitudes, during three different phenological stages of rice. Data from vegetation relevés was analyzed using TWINSPAN, resulting in the identification of four main plant community types related to the different stages of rice growth: Echinochloa crus-galli–Paspalum distichum, Spirodela polyrrhiza–Lemna minor, Monochoria vaginalis s.l.–Marsilea quadrifolia, and Cyperus difformis–Ammannia baccifera. Complementary direct (canonical correspondence analysis) and indirect gradient analyses (detrended correspondence analysis) confirmed these communities’ separation and indicated that the most significant environmental factors affecting plant community distribution were soil water content and soil pH. Moreover, out of 72 segetal species of investigated rice paddies, 12 species were alien to Iran, indicating that this agroecosystem provides an important source for the introduction, distribution, and possible spread of alien species into other adjacent ecosystems. Our findings contribute to the knowledge of detecting patterns of weed composition and distribution in rice paddy ecosystems, as well as their interpretation in relation to environmental gradients. They can support the establishment of ecological weed management practices in northern Iran's paddy fields.

Rising atmospheric CO2 concentration affect weedy rice growth, seed shattering and seedbank longevity

AbstractWeedy rice (Oryza sp.) is one of the most troublesome global weeds in cultivated rice. Its troublesome status is associated with characteristics such as seed shattering and dormancy, allowing for long‐term reinfestation and persistence in rice fields. However, the role of rising carbon dioxide levels (CO2) and other climate variables on these characteristics has not, to date, been assessed. The current research objectives were to evaluate two aspects related to climatic change, increased CO2 concentration (400 ± 50 μmol mol−1 and 700 ± 50 μmol mol−1) and water management (continuous and alternate‐wetting drying), to assess plant development, seed shattering and seedbank longevity of weedy rice. Our results indicated that elevated CO2 (700 ± 50 μmol mol−1) increased weedy rice growth and biomass, seed shattering and lengthened viability within the seedbank. Water management did not affect weedy rice growth, seed shattering and seed dormancy. These results suggest that in areas where weedy rice is dominant, its seed bank persistence and potential competition may be exacerbated with rising CO2 levels, with negative consequences for rice production.

Arkansas Rice: Herbicide Resistance Concerns, Production Practices, and Weed Management Costs

An online survey to better understand current weed management practices and concerns in Arkansas rice was distributed in the fall of 2020. A total of 123 respondents from across the Arkansas rice growing region returned the survey covering a total of 236,414 rice hectares, representing about 40% of the planted Arkansas rice hectares in 2020. The most problematic weeds were Echinochloa crus-galli (L.) P. Beauv. (ECG), Cyperus spp., and Oryza sativa L. (weedy rice), respectively, in flooded rice, and ECG, Amaranthus palmeri S. Wats., and Cyperus spp., respectively, in furrow-irrigated rice. Most respondents (78%) reported high concern with herbicide-resistant weeds, and crop rotation (>74%) was the most common strategy listed to control and mitigate the development of herbicide-resistant weeds. A chi-square test of homogeneity showed that strategies implemented to control herbicide-resistant weeds and mitigate the evolution of herbicide-resistant weeds were not dependent on occupation type (farmer, consultant, or industry rep) nor on years of involvement in rice production. Respondents failed to control ECG 44% of the time with their first postemergence herbicide. After initial herbicide failure, 53% of respondents stated two additional herbicide applications were required to control ECG escapes while another 21% of respondents stated it was never controlled. The average ECG population at 2020 harvest was between 0.1 and 1.0 plant m−2 according to 44% of the respondents; however, 41% of respondents indicated an ECG density of 2 to 10 plants m−2 at 2020 harvest. The reported annual average cost of herbicides for rice weed control was $266.40 ha−1 with ECG accounting for 81% of the total cost. Average yield loss attributed to ECG was estimated to be 505–959 kg ha−1 (economic loss of $134–254 ha−1). However, yield loss in the most heavily infested fields was estimated to be 757–1,464 kg ha−1 (economic loss of $200–387 ha−1). Effective, non-chemical approaches to weed management were ranked as the least important current research or educational effort, indicating a paradigm shift in rice producers' weed control line of thought is needed with dwindling herbicide options due to herbicide resistance.

Cyperus iria Weed Growth, Survival, and Fecundity in Response to Varying Weed Emergence Times and Densities in Dry-Seeded Rice Systems

Cyperus iria is amongst the most threatening weeds of rice in Sri Lanka, India, Pakistan, and the Philippines. Broad knowledge about the ecology and fecundity of C. iria is important for its effective management. Field studies were conducted over two seasons (wet (WS) and dry seasons (DS)) to investigate the influence of C. iria populations (40 and 80 plants m−2) on its growth, survival, and fertility, with four emergence times, 3, 15, 30, and 45 d after rice emergence (DARE), during 2013. We postulated that (a) higher plant density of this weed would result in more biomass production and viable seeds per unit area, (b) interference of rice would reduce the biomass production and fecundity of this weed, and (c) delaying weed emergence would lead to downsizing of its percent survival and seed bank enrichment in soil. The results indicated that rice interference decreased C. iria growth and seed production as compared with those of plants established without rice interference. A linear decrease in the percent survival of C. iria without rice and a sigmoid decrease with rice were observed during both seasons. Plant height of C. iria was moderately affected up to 30 DARE, and a significant reduction was observed at 45 DARE. There was a linear relationship between C. iria shoot dry weight and seed number plant −1, across-weed density, seeding rate of rice, and emergence time. C. iria seed production, 1000-seed weight, and seed yield were greater when seedlings emerged simultaneously with the rice crop (3 DARE) than when they emerged late. Under rice weed interference growth, the production of viable seeds was completely stopped at 45 DARE. The delay in the emergence of C. iria up to 45 DARE was unable to produce seed in both seasons. The results of the current studies advocate that the emergence, weed biomass, and seed production of C. iria can be checked by adopting suitable cultural weed management practices, which can impede the emergence of weed relative to rice. These practices, enabling the respective crops to be more competitive, will foster integrated weed management approaches, thus offering a key role in seed detection to the soil seed reservoir or pool by notorious weeds in the field.