Rice Ecosystem, Allelopathy and Environment – A Review

Enhanced weed control can occur when chemical herbicides are applied in combination with microbial agents. Synergy between chemicals and biologicals was first observed with fungal bioherbicides. Use of a herbicide with a fungal-bioherbicide does not appear to widen the weed spectrum of the bioherbicide but does increase the efficacy. In some cases the synergy may result from a suppression of phytoalexin synthesis by the chemical herbicide. Use of synthetic herbicides to synergize mycoherbicides will in some cases reduce herbicide use rate and improve mycoherbicide efficacy. We report here that synergy occurs between chemical herbicides and bacterial agents. We have discovered that bacteria which cause little or no injury to weeds when applied alone can enhance the stability of low levels of chemical herbicides to control a broad spectrum of weeds. We term this synergistic combination the X-tend system. In the first year of X-tend field trials, the level of weed control required for commercialization was not obtained consistently across geographic locations. Consistency will need to be improved through selection of more robust microbial strains and/or improvements in formulations

The continued use of synthetic herbicides to control weeds leads to environmental pollution and health issues. Consequently, chemical formulations have been increasingly banned. However, sustainable solutions are lacking in the market. Alternatively, valorisation of phytotoxic waste to reduce the herbicides use promotes sustainability, meeting circular economy. We aimed at assessing the herbicidal potential of aqueous extracts of waste from the management of invasive plants (Acacia dealbata bark, Oxalis pes-caprae biomass) and agri-food (spent coffee grounds) on common urban weeds (Achillea ageratum, Conyza canadensis and Dittrichia viscosa) in Portugal. In vitro (paper and soil) and pot assays (soil) were conducted to test the pre-emergence (germination and seedlings) and post-emergence (well-stablished plants) effect of waste extracts on these weeds. Extracts reduced pre-emergence performance of weeds, but marginally affected post-emergence parameters. Germination was inhibited up to 83% by O. pes-caprae in A. ageratum, up to 88% and 87% by A. dealbata and O. pes-caprae in C. canadensis, and up to 70% by concentration in D. viscosa. A. dealbata and O. pes-caprae extracts also drastically reduced radicle length (30% and 55% in A. ageratum, 77% and 81% in C. canadensis, 90% and 92% in D. viscosa, respectively). However, soil neutralized the inhibitory pre-emergence effect. The main findings highlight that the use of A. dealbata and O. pes-caprae extracts as bioherbicides may require an additional synthetic herbicides application, as extracts alone cannot fully control urban weeds in areas without soil. Combining bioherbicides and commercial formulations still reduces the application of toxic chemicals, promoting sustainability.

Botolempangan Village in Bontoa Sub-district is one of the centers of paddy rice production in Maros Regency, with characteristics of rain-fed paddy fields that have many obstacles to weed infestation, especially if the dry season is abandoned from rice farming activities, before being planted during the rainy season where farmers are very dependent on the use of herbicides. Dependence on the use of synthetic (inorganic) herbicides occurs from the pre-growth period of seeds, seedlings to the maintenance process. High costs result in considerable inefficiencies in rice farming. Training in technology transfer efforts to make Organic Herbicide Formulations, and their applications are carried out to increase the Empowerment and Efficiency of rice farming on Rainfed Rice Fields. With the efficiency target is to increase the profit of paddy rice farming, minimizing inorganic herbicide inputs. The output of this activity ultimately produces products that can be applied to at least reduce or reduce the use of inorganic herbicides. At the end of the activity, farmer business groups are able to produce and apply Organic Herbicide Formulations on Demoplots on Farmer-Owned Land.

Herbicides play a crucial role in modern agriculture by controlling weeds and ensuring sustainable crop productivity. However, the use of herbicides has raised concerns regarding their contamination, posing serious threat to the environment, biodiversity, and food safety. Recent trends indicate a decline in the overall volume of herbicides usage, suggesting a shift towards more specific and targeted formulations of herbicides. Also, there has been an increased use of systemic and pre-emergence herbicides. The global agriculture still faces several challenges because of the adverse environmental impacts caused by herbicide contamination, both at the application site and offsite. In view of the growing concern, it is necessary to develop new herbicides with greater selectivity or bio-based herbicide that can degrade after successful control of the intended weed population and minimize or eliminate the environmental hazards. Furthermore, the adoption of integrated weed management practices rather than prolonged and repeated use of herbicide in agriculture can effectively reduce the growth of herbicide-resistant weed populations. The present review is a single valuable resource, providing insights into the recent trends and future challenges associated with herbicide use in modern agriculture, with a focus on human health and food safety. Also, we emphasize the advancements in herbicide technology, emergence of new herbicide-resistant weed species, regulatory considerations, and alternative approaches in herbicide use, all of which are particularly valuable to agroecology, policymakers, and stakeholders.Graphical

This series of papers was presented at the Symposium on Integrating Alternative Strategies into Weed Management held during the 1994 ASA‐CSSA‐SSSA annual meetings in Seattle. The program was sponsored by Division A‐8 (Integrated Agricultural Systems) and NCR‐177—a North Central Region technical working group on Non‐Herbicide Alternatives for Weed Management, the Weed Science Society of America, and Divisional co‐sponsors A3, A5, A4, and C3. Executive Summary Weeds are a major problem in production agriculture throughout the world. Weeds have been part of the challenge in maintaining adequate food supplies since agrarian ways of life evolved. In order to maintain yields of plants and animals, weeds must be controlled. In 1992, losses due to weeds in the USA and Canada were estimated at $4.1 billion, with estimated losses exceeding $19 billion if herbicides were not available. However, problems with herbicides, including groundwater and surface water contamination, other offsite movement, and pesticide residues in food, has sparked public awareness and restrictions of herbicide use. These problems have challenged weed scientists to consider alternative and integrated systems of weed management to reduce herbicide inputs and impacts. In order to determine what the term “alternative” weed management strategies represents, one must first define the conventional strategies producers use. If this symposium were presented in the 1950s, we probably would have described chemical‐based strategies that were developed around such organic chemicals as 2,4‐D, simazine, and atrazine, and some inorganic chemicals. Use rates of these chemicals would average about 4 to 6 Ib ai per acre. These herbicides would be presented as an alternative to hand‐pulling, cultivation, more cultivation, and inorganic chemicals applied at rates of 60 to 100 lb/acre. Use of herbicides reduced the number of cultivations and labor needed for effective weed control and allowed an increase in farm size. In fact, farm labor requirements in the USA decreased by 25% from 1947 to 1986, while chemical use increased by 800% (Osteen and Szmedra, 1989). In the 1990s, our conventional strategies for weed management are organic chemical based. The herbicide families used today include some of the older herbicides used in the 1950s including 2,4‐D and the triazines. More recently, herbicide families added to the chemical arsenal include sulfonyl ureas, immidiazilinones, and aryloxyphenoxies. Some of the newer herbicides are used at rates 10 to 100 times lower than the older herbicides. Nevertheless, herbicide use has increased in the USA from 71 million lb ai in 1964 to 456 million lb ai in 1986. Virtually all the acreage of some crops is treated with some herbicide. The application of herbicide saves labor and time, has given excellent control of some of the most persistent weeds, has increased yields, and has allowed the growth of farm sizes. Increased herbicide use has not been without cost or public concern. Producers are being pressured to reduce herbicide use on crops. Government regulations reveal a society concerned with sometimes real and often perceived risks that are associated with herbicides. These risks include: contamination of ground and surface water, herbicide residues that may increase the risk of human or animal health problems, and the harming of already endangered plant species. As agriculture steps into the 21 st century, agricultural scientists must help producers meet the increasing demand for food while providing methods that minimize weed interference (which probably does not equal weed control) and undesirable environmental impact. This does not mean throwing out all herbicides. The “alternative” weed management tactics described in the following technical reports presented at the symposium encompass a range of integrated methods including crop competition, cover crops, mechanical control, and biocontrol agents. Considerations and challenges for developing integrated systems are also discussed, including the governmental policy issues that help or hinder adoption of alternative weed management systems, the need to understand weed biology and ecology to make systems work, and techniques used to develop alternative weed management strategies. Several other topics were considered at the symposium, such as the environmental consequences of weed management, the use of crop rotation, and extension challenges. The symposium drew about 200 participants and featured highly spirited discussions. The day following the symposium, a volunteer session had about 20 posters devoted to alternative weed management strategies in rangeland, crops, and Christmas tree plantations. The following papers provide information on the challenges and guidance on the development of alternative strategies for weed management. Through adoption and modification, we can meet the challenges of today and the hture. On behalf of NCR‐177 and others, we would like to thank all those who contributed to this program. Sharon Clay and Steve Oberle Symposium organizers ( clay@mg.sdstate.edu )

Bioherbicides: Dead in the water? A review of the existing products for integrated weed management

Allelopathic compounds are metabolites released from plants that might be beneficial or detrimental to the growth of receptor plants. These compounds are involved in the environmental complex of managed or natural ecosystems. Allelopathic compounds have been shown to play important roles in the determination of plant diversity, dominance, succession, and climax of natural vegetation and in the plant productivity of agroecosystems. The overuse of synthetic agrochemicals often causes environmental hazards, an imbalance of soil microorganisms, nutrient deficiency, and change of soil physicochemical properties, resulting in a decrease of crop productivity. The incorporation of allelopathic substances into agricultural management may reduce the use of synthetic herbicides, fungicides, and insecticides and lessen environmental deterioration. Scientists in many different habitats around the world have demonstrated the above examples previously. It is known that most volatile compounds, such as terpenoids, are released from plants in drought areas. In contrast, water-borne phytotoxins, such as phenolics, flavonoids, or alkaloids, are released from plants in humid zone areas. Both allelopathy and autointoxication play an important mechanism in regulating plant biodiversity and plant productivity. A unique case study of a pasture-forest intercropping system, which is particularly emphasized here, could be used as a model for forest management. After the deforestation of coniferous or hardwood forests, a pasture grass, kikuyu grass (Pennisetum clandestinum), was transplanted onto the land. The grass was quickly established within 6 months. Significant suppression of weed growth by the kikuyu grass was found; however, the growth of coniferous or hardwood plants was not suppressed but stimulated. This example as well as others described in this text clearly indicate that allelopathy plays a significant role in sustainable agriculture. Nevertheless, room for allelopathic research in the next century is available for biologists, biochemists, biotechnologists, and chemists. Future allelopathic research should focus on the following tasks: (1) a continuous survey of potential allelochemicals from natural vegetation or microorganisms, (2) the establishment of practical ways of using allelochemicals in the field, (3) to understand the mode of action of allelopathic chemicals in receptor organisms, (4) to understand the role of allelopathic chemicals in biodiversity and ecosystem function, (5) to explore advanced biotechnology for allocating allelopathic chemical genes in plants or microorganisms for biological control, and (6) to challenge the natural product chemists to develop a better methodology for isolating allelopathic compounds or their degraded compounds from the environment, particularly the soil environment.

Phytotoxic effects of Salvia rosmarinus essential oil on Acacia saligna seedling growth

Weeds cause significant yield loss in many agriculture crops; thus, management practices are urgently needed to alleviate losses while conserving environmental and human health. This study aimed to evaluate the allelopathic potential of Wedelia leaf and flower extracts on the germination and early growth stage of three plant species. The research was conducted using a completely randomized design experiment with two factors and four replicates. The first factor was extract sources: leaves (S1) and flowers (S2). The second factor was the concentration: control (C0) and extract concentrations of 1% (C1), 5% (C5), and 10% (C10). The extract was tested on three different plant species: soybean (Glycine max), nutsedge (Cyperus rotundus), and billygoat weed (Ageratum conyzoides). Fifty seeds of three different plants were germinated separately in Petri dishes and treated using Wedelia extracts. The allelochemicals in Wedelia leaf and flower extracts inhibited germination and induced abnormal sprouting. Wedelia leaf extract showed the most pronounced inhibitory effects and highest inhibition levels across all measured parameters. Moreover, a clear concentration-response relationship was observed, where increased extract concentration increased the degree of inhibition. These findings contribute to the development of bioherbicides and can help reduce the use of synthetic herbicides for more sustainable agriculture. Keywords: Ageratum conyzoides, bioherbicide, Cyperus rotundus, Glycine max, weed control

The indiscriminate use of synthetic herbicides reduces its effectiveness. Bioherbicides produced with metabolites emerge as an alternative to managing weeds. We aimed to analyze the phytotoxic potential of the essential oil of Vanillosmopsis arborea (EOVA) and the α-bisabolol molecule, its main component. We evaluated the effects of EOVA and α-bisabolol at different concentrations on the germination, growth, antioxidant metabolism, and photosynthesis of different species. EOVA and α-bisabolol showed promising phytotoxic effects on the germination and initial growth of the weed Senna occidentalis, inhibiting the activity of the antioxidant enzymes and increasing lipid peroxidation. α-Bisabolol reduced the weed seedling growth by inducing oxidative stress, which suggests a greater role in postemergence. Moreover, in the weed postemergence, both EOVA and α-bisabolol caused damage in the shoots, reduced the chlorophyll content, and increased lipid peroxidation besides reducing photosynthesis in S. occidentalis. Overall, we suggest the promising action of α-bisabolol and EOVA as bioherbicides for weed control.

Allelopathic compounds are metabolites released from plants that might be beneficial or detrimental to the growth of receptor plants. These compounds are involved in the environmental complex of managed or natural ecosystems. Allelopathic compounds have been shown to play important roles in the determination of plant diversity, dominance, succession, and climax of natural vegetation and in the plant productivity of agroecosystems. The overuse of synthetic agrochemicals often causes environmental hazards, an imbalance of soil microorganisms, nutrient deficiency, and change of soil physicochemical properties, resulting in a decrease of crop productivity. The incorporation of allelopathic substances into agricultural management may reduce the use of synthetic herbicides, fungicides, and insecticides and lessen environmental deterioration. Scientists in many different habitats around the world have demonstrated the above examples previously. It is known that most volatile compounds, such as terpenoids, are released from plants in drought areas. In contrast, water-borne phytotoxins, such as phenolics, flavonoids, or alkaloids, are released from plants in humid zone areas. Both allelopathy and autointoxication play an important mechanism in regulating plant biodiversity and plant productivity. A unique case study of a pasture-forest intercropping system, which is particularly emphasized here, could be used as a model for forest management. After the deforestation of coniferous or hardwood forests, a pasture grass, kikuyu grass (Pennisetum clandestinum), was transplanted onto the land. The grass was quickly established within 6 months. Significant suppression of weed growth by the kikuyu grass was found; however, the growth of coniferous or hardwood plants was not suppressed but stimulated. This example as well as others described in this text clearly indicate that allelopathy plays a significant role in sustainable agriculture. Nevertheless, room for allelopathic research in the next century is available for biologists, biochemists, biotechnologists, and chemists. Future allelopathic research should focus on the following tasks: (1) a continuous survey of potential allelochemicals from natural vegetation or microorganisms, (2) the establishment of practical ways of using allelochemicals in the field, (3) to understand the mode of action of allelopathic chemicals in receptor organisms, (4) to understand the role of allelopathic chemicals in biodiversity and ecosystem function, (5) to explore advanced biotechnology for allocating allelopathic chemical genes in plants or microorganisms for biological control, and (6) to challenge the natural product chemists to develop a better methodology for isolating allelopathic compounds or their degraded compounds from the environment, particularly the soil environment.

Purpose. To study the influence of predecessors on the formation of weed and pest species composition in spring barley sowings and the grain yield loss. Methods. Field, physical, mathematical and statistical. Results. The most common weed species in spring barley sowings during vegetation season are the following: Cirsium arvense, Sonchus oleraceus, Ambrosia artemisiifolia, Elymus repens, Sinapis arvensis, Consolida regalis, and Polygonum lapathifolium. The number of weeds per 1 m2 of spring barley sowings affected the amount of grain losses. After pealosses, the lowest grain loss (0.01 to 0.24 t/ha) was at the number of weeds from 5 to 10 per m2. The increase in the number of weeds has contributed to the increase in the grain loss. However, this figure varied over weed species. Thus, under the infestation with Sinapis arvensis and Consolida regalis, the grain yield loss was significantly lower compared to the control with the largest number of weeds. The largest grain loss occurred from Cirsium arvense and Sonchus oleraceus reaching 0.53–0.53 t/ha in at the number of weeds 20 per m2. Given the Polygonum lapathifolium, Ambrosia artemisiifolia, Sinapis arvensis, and Elymus repens, this figure ranged from 0.19 to 0.34 t/ha. When spring barley was grown after sugar beet, grain yield loss was significantly lower than under the number of weeds from 12 to 20 per 1 m2. However, the trend of falling grain yield caused by weeds was similar. The smallest grain loss caused Sinapis arvensis and Consolida regalis, while the largest one was caused by root and shoot and rhizome weeds. The number of pests in spring barley crops varied from 1.0 to 1.8 per 1 m2 (plant). In the case of spring barley cultivation after pea, the grain yield loss varied from 0.52 to 0.73 t/ha, while after sugar beet from 0.34 to 0.41 t/ha, varying over the years of the study. Because the air temperature was similar during the pest development period, the number of pests varied little. Lower grain yield loss after sugar beet was due to fewer common pests. Conclusions. It was found that the largest grain yield loss was caused by such weeds species as Cirsium arvense, Sonchus oleraceus, Ambrosia artemisiifolia, and Elymus repens ranging between 0.47 and 0.55 t/ha in the amount of 20 plants per m2. Sinapis arvensis and Consolida regalis caused the lowest grain loss ranging from 0.26 to 0.28 t/ha. Under Sinapis arvensis, this figure ranged from 0.02 to 0.34 t/ha, depending on the weed number. In the sowing of spring barley, Schizaphis graminum Rond., Lema lichenis Voet., Phyllotreta vittula Redt, Carabidae, Aelia acuminata, and Eurygaster integriceps Put. were found. Pest control in spring barley sowings provides 0.52 to 0.73 t/ha of grain yield growth after pea cultivation and 0.34 to 0.41 t/ha after sugar beet.

SummaryThe effects of herbicide dose on rice‐weed competition were investigated to develop a combined model, which can be utilised to estimate an optimum herbicide dose for a given weed density in paddy rice cultivation. Field studies were conducted in Suwon for rice‐Echinochloa crus‐galli competition and Iksan for rice‐Eleocharis kuroguwai during 2007. The competitive effect of the weeds E. crus‐galli and E. kuroguwai decreased with increasing doses of flucetosulfuron and azimsulfuron, respectively, in the same manner as the standard dose–response curve. The combination of the rectangular hyperbolic model and the standard dose–response curve adequately described the complex effects of herbicide dose and weed competition on rice yield. Parameter estimates were used with the model to predict rice yield and estimate the doses of flucetosulfuron and azimsulfuron required to restrict rice yield loss caused by E. crus‐galli and E. kuroguwai, respectively, to an acceptable level. For a rice yield of 5.0 t ha−1, the model recommended flucetosulfuron doses of 8.7, 13.4 and 20.1 g a.i. ha−1 when infested with E. crus‐galli at 12, 24 and 48 plants m−2 respectively. For a rice yield of 5.2 t ha−1, the model recommended azimsulfuron doses of 3.9, 7.5 and 12.6 g a.i. ha−1 when infested with E. kuroguwai at 24, 48 and 96 plants m−2 respectively. The theoretical outputs of the combined model appear robust and indicate there are opportunities for reduced herbicide use in the field. These now require evaluation under field conditions.

The objective of this research was to explore the influence that weed decision threshold (DT; expressed as plants m−2), weed spatial distribution patterns, and spatial resolution of sampling have on potential reduction in herbicide use under site-specific weed management. As a case study, a small plot located in a typical corn field in central Spain was used, constructing very precise distribution maps of the major weeds present. These initial maps were used to generate herbicide prescription maps for each weed species based on different DTs and sampling resolutions. The simulation of herbicide prescription maps consisted of on/off spraying decisions based on information from two different approaches for weed detection: ground-based vs. aerial sensors. In general, simulations based on ground sensors resulted in higher herbicide savings than those based on aerial sensors. The extent of herbicide reductions derived from patch spraying was directly related to the density and the spatial distribution of each weed species. Herbicide savings were potentially high (up to 66%) with relatively sparse patchy weed species (e.g., johnsongrass) but were only moderate (10 to 20%) with abundant and regularly distributed weed species (e.g., velvetleaf). However, DT has proven to be a key factor, with higher DTs resulting in reductions in herbicide use for all the weed species and all sampling procedures and resolutions. Moreover, increasing DT from 6 to 12 plants m−2resulted in additional herbicide savings of up to 50% in the simulations for johnsongrass and up to 28% savings in the simulations for common cocklebur. Nonetheless, since DT determines the accuracy of patch spraying, the consequences of using higher DTs could be leaving areas unsprayed, which could adversely affect crop yields and future weed infestations, including herbicide-resistant weeds. Considering that the relationship between DT and accuracy of herbicide application depends on weed spatial pattern, this work has demonstrated the possibility of using higher DT values in weeds with a clear patchy distribution compared with weeds distributed regularly.

Long-term studies are crucial for evaluating how intercropping affects the agronomic, environmental, and socio-economic sustainability of sugarcane systems. Intercropping with cover crops is expected to improve soil fertility and reduce herbicide use; however, its long-term effects on yield, weed dynamics, and production costs remain unclear, particularly under tropical conditions. Weed pressure has been hypothesized to drive yield decline over time, yet the temporal evolution of weed communities and their consequences for system sustainability remain poorly understood. We hypothesized that intercropping would modify ecosystem functions and services by increasing weed diversity and soil fertility, reducing herbicide use, and also increasing labor and production costs. To test this hypothesis, we conducted the first 7-year field experiment on Reunion Island, comparing four sugarcane intercropping systems with conventional chemical and low weed control systems. A multi-criteria approach assessed weed community dynamics, soil fertility, sugarcane yield and quality, herbicide use, labor, and economic performance over a complete crop cycle, including multiple ratoons. We show that weed pressure increased over time in both chemical and intercropping systems due to greater weed cover and species richness. Weed community structure differed during the first 3 years but later homogenized under sugarcane dominance. This increase led to more manual weeding in intercropping systems and to increased herbicide use in chemical ones, resulting in a 61% reduction in herbicide use under intercropping. After 7 years, soil chemical and biological fertility remained unchanged, while physical fertility improved with companion crop and weed development. Sugarcane yield and sucrose content were maintained, but production costs and working hours increased. This study demonstrates that sugarcane intercropping reduces herbicide dependence without compromising yield, though at higher labor costs. Systems maintaining spontaneous flora in inter-rows appear to offer a promising compromise for sustainable weed management. Further research on this system should be conducted in different pedoclimatic conditions.