Optimal Weed Management Research Articles

Metsulfuron methyl: A versatile low dose and high efficiency herbicide for optimal weed management in transplanted rice

Metsulfuron methyl: A versatile low dose and high efficiency herbicide for optimal weed management in transplanted rice

Dynamic changes in weed abundance and biodiversity following different green manure establishment

Weeds have a negative impact on agricultural production by competing with cultivated crops for resources and fostering conditions conducive to disease and insect pest dissemination. Hence, optimal weed management is of paramount importance for sustainable agricultural. In this study, the ability of four distinct green manure species to suppress weeds was determined in a field experiment conducted in Chongqing, Southwest China. After cultivating the green manure species, the weed density and diversity were monitored over the following year. The findings highlight a notable trend in the suppressive ability of green manures, with increased suppression observed from November to March, an optimal level observed from March to May, and a gradual decline observed thereafter. Poaceae (Lolium perenne L.) demonstrated the highest efficacy in suppressing weeds. The meta-analysis underscore the exceptional suppressive effects of poaceous green manures on weed as well and prove sustained planting for three or more consecutive years yielded superior weed suppression outcomes. Green manure had the most prominent inhibitory effect on poaceae weeds, followed by Polygonaceae and Caryophyllaceae. The field experiment also investigated the effect of green manures on weed community composition, they increased in the proportion of perennial weeds within these communities. This study offers valuable insights that can guide policymakers, agricultural experts, and farmers in devising effective weed management strategies. By highlighting the potential benefits of green manures and unraveling their nuanced impact, this study contributes to the arsenal of sustainable agricultural practices.

Strategic tillage in Australian conservation agricultural systems to address soil constraints: How does it impact weed management?

AbstractIn the conservation agricultural systems practised in Australia, cultivation is not commonly utilised for the purpose of weed control. However, occasional use of tillage (strategic tillage) is implemented every few years for soil amelioration, to address constraints such as acidity, water repellence or soil compaction. Depending on the tillage method, the soil amelioration process buries or disturbs the topsoil. The act of amelioration also changes the soil physical and chemical properties and affects crop growth. While these strategic tillage practices are not usually applied for weed control, they are likely to have an impact on weed seedbank burial, which will in turn affect seed dormancy and seedbank depletion. Strategic tillage impacts on seed burial and soil characteristics will also affect weed emergence, plant survival, competitive ability of weeds against the crop and efficiency of soil applied pre‐emergent herbicides. If growers understand the impacts of soil amelioration on weed demography, they can more effectively plan management strategies to apply following the strategic tillage practice. Weed seed burial resulting from a full soil inversion is understood, but for many soil tillage implements, more data is needed on the extent of soil mixing, burial of topsoil and the weed seedbank, physical control of existing weeds and stimulation of emergence following the tillage event. Within the agronomic system, there is no research on optimal timing for a tillage event within the year. There are multiple studies to indicate that strategic tillage can reduce weed density, but in most studies, the weed density increases in subsequent years. This indicates that more research is required on the interaction of amelioration and weed ecology, and optimal weed management strategies following a strategic tillage event to maintain weeds at low densities. However, this review also highlights that, where the impacts of soil amelioration are understood, existing data on weed ecology can be applied to potentially determine impacts of amelioration on weed growth.

Impact of Integrated Weed Management on Bulb Yield of Onion

The experiment was conducted at Regional Spices Research Centre, Bangladesh Agricultural Research Institute, Magura, Bangladesh during 2016-2017 and 2017- 2018 to optimize weed management practice for onion bulb production through Integrated Weed Management (IWM). The experiment was laid out in a Randomized Complete Block Design with three replications. Two different herbicides (Oxadiazon and Pendimethalin) with different doses in combination with hand weeding (HW) were used as treatments. The total number of treatments were 12 viz. T1=Oxadiazon@1.0 l/ha, T2=Oxadiazon@1.5 l/ha, T3= Oxadiazon@2.0 l/ha, T4= Oxadiazon@1.0 l/ha + one HW at 45 DAT (Days After Transplanting), T5= Oxadiazon@1.5 l/ha + one HW at 45 DAT,T6= Oxadiazon@2.0 l/ha + one HW at 45 DAT, T7=Pendimethalin@1.0 l/ha, T8=Pendimethalin@1.5 l/ha, T9= Pendimethalin@1.0 l/ha + HW at 45 DAT, T10= Pendimethalin@1.5 l/ha+ HW at 45 DAT, T11= Weed free and T12 = Weedy check (control). The onion var. BARI Piaz-1 was used as the test crop. The highest bulb yield (7.63 tha-1 in 2016 & 9.56 t ha-1in 2017) and benefit cost ratio (2.14 in 2016 and 2.46 in 2017) were obtained from T6= Oxadiazon@2.0 l/ha + one hand weeding at 45 DAT while the lowest bulb yield (4.22 t ha-1in 2016 and 6.28 t ha-1in 2017) was obtained from T12 = Weedy check (control), while lowest benefit cost ratio (1.33 in 2016 and 1.74 in 2017) from treatment T11 =Weed free. It was concluded that Oxadiazon@2.0 l/ha with one hand weeding at 45 days after transplanting performed better for controlling weed and maximizing bulb yield of onion.
 Bangladesh Agron. J. 2020, 23(1): 83-89

Role of Soil Sorption and Microbial Degradation on Dissipation of Mesotrione in Plant-Available Soil Water

Mesotrione is a carotenoid biosynthesis-inhibiting herbicide labeled for pre-emergence and postemergence weed control in corn production. Understanding the factors that influence the dissipation of mesotrione in soil and in the plant-available water (PAW) is important for the environmental fate assessment and optimal weed management practices. The present research investigated the role of soil properties and microbial activities on the interrelated sorption and degradation processes of mesotrione in four soils by direct measurements of PAW. We found that mesotrione bound to the soils time dependently, with approximately 14 d to reach equilibrium. The 24-h batch-slurry equilibrium experiments provided the sorption partition coefficient ranging from 0.26 to 3.53 L kg(-1), depending on soil organic carbon and pH. The dissipation of mesotrione in the soil-bound phase was primarily attributed to desorption to the PAW. Degradation in the PAW was rapid and primarily dependent on microbial actions, with half-degradation time (DT(50)) <3 d in all four soils tested. The rapid degradation in the PAW became rate limited by sorption as more available molecules were depleted in the soil pore water, resulting in a more slowed overall process for the total soil-water system (DT(50) <26 d). The dissipation of mesotrione in the PAW was due to microbial metabolism and time-dependent sorption to the soils. A coupled kinetics model calibrated with the data from the laboratory centrifugation technique provided an effective approach to investigate the interrelated processes of sorption and degradation in realistic soil moisture conditions.

Modeling of Glyphosate Application Timing in Glyphosate-Resistant Soybean

The introduction of herbicide-resistant crops and postemergence herbicides with a wide action spectrum shifted the research focus from how to when crops should be treated. To maximize net return of herbicide applications, the evolution of weed–crop competition over time must be considered and its effects quantified. A model for predicting the yield trend in relation to weed removal time, considering emergence dynamics and density, was tested on data from glyphosate-resistant soybean grown in cropping systems in Italy and Argentina. Despite an ample variation of weed emergence dynamics and weed load in the four trials, the model satisfactorily predicted yield loss evolution. The estimated optimum time for weed control (OTWC) varied from about 18 d after soybean emergence in Argentina to 20 to 23 d in Italy, with time windows for spraying ranging from 14 to 28 d. Within these limits a single glyphosate application ensures good weed control at low cost and avoids side effects like the more probable unfavorable weed flora evolution with double applications and the presence of residues in grains. Despite the apparent simplicity of weed control based on nonselective herbicides, the study outlines that many variables have to be considered to optimize weed management, particularly for the time evolution of the infestation and, subsequently, a proper timing of herbicide application.

A bioeconomic model for determining the optimal response strategies for a new weed incursion

Invasions by non-indigenous plant species pose serious economic threats to Australian agricultural industries. When a new invader is identified a rapid response is critical, particularly if the invasive species has the ability to spread rapidly. An early decision is required whether to attempt to eradicate or contain the infestation, or do nothing and leave it to landholders to manage. These decisions should be based on economic considerations that account for long term benefits and costs. This paper describes a bioeconomic simulation framework with a mathematical model representing weed spread linked to a dynamic programming model to provide a means of determining the economically optimal weed management strategies over time, from the government’s perspective. The modelling framework is used to evaluate hypothetical case study invasive weed control scenarios in the Australian cropping systems. The benefit–cost ratios of invasion control are shown to be generally very high and clearly, there are significant benefits to be achieved by controlling highly invasive weeds when initial infestations are at a low level. Even if the invasion cannot be eradicated due to its high invasiveness or budget constraints, it still pays to maintain invasions at low levels.

Optimal weed management in crop rotations: incorporating economics is crucial

Van Den Berg F, Gilligan CA, Gerdessen JC, Gregoire LAH &amp; VanDen Bosch F (2010). Optimal weed management in crop rotations: incorporating economics is crucial. Weed Research50, 413–424.SummaryAlthough the effects of crop rotation sequence and length on weed population dynamics have been studied, it is not clear whether or not the best strategy, from a weed population dynamics point of view, is also the economic optimal strategy. It is also not clear which biological and economic parameters are most important in determining this optimal strategy. We use a density‐dependent periodic matrix model, integrated with an economic model, to study the effect of rotation length and weed control on the average annual net profit (ANP). The system of the weed Persicaria maculosa in carrots (crop A) and spring wheat (crop B) is used as an example case study. The bio‐economic model shows that income is roughly constant with rotation length, apart from the shortest rotation sequence. These results are in agreement with a previous model study, which was restricted to biological dynamics. However, where the purely biological model suggests that weeding effort should be focussed on spring wheat years in the rotation, our bio‐economic model shows that this is not a viable economic strategy. In fact, the mean ANP over a rotation is mainly determined by the ANP in carrot years (where the gross margin is high) and depends on the balance between the increase in seed population density in carrot years and its decrease in wheat years, in combination with weeding costs. The model can easily be extended to incorporate other damaging organisms, making the model broadly suitable for analysing a range of weed management strategies from an economic perspective.

Planting Date and Glyphosate Timing on Soybean

Planting date of soybean may be one factor that affects the crop's ability to compete with weeds. Field experiments were conducted over 3 yr at two locations in Illinois to determine whether planting date affects optimal weed management strategies and the critical time of weed removal (CTWR) in glyphosate-resistant soybean. Across planting dates, a PRE application of metolachlor plus metribuzin followed by a single glyphosate application at a 10- or 20-cm weed height at Monmouth or at a 20-cm weed height at Urbana was effective at protecting yield. At Monmouth, higher yields occurred with sequential glyphosate applications than with a single application in the early planting in 2 yr when weeds were removed at a height of 10 cm. Across planting dates, highest yields at Monmouth occurred with a single glyphosate application when weeds were 20 to 30 cm tall. At Urbana, the CTWR was not affected by planting date and occurred between 176 and 290 growing-degree days (GDD) after planting, corresponding to the V1...

The social construction of weeds: different reactions to an emergent problem by farmers, officials and researchers

Rapid population increase in southern Benin has changed the prevailing system of shifting cultivation into one of more permanent land use. New herbaceous weeds exacerbated rural poverty through crop failure, higher labour inputs, rising costs of production and reduced availability of suitable land. We investigated how different actors reacted to the emergence of weeds, in terms of the construction of knowledge, labour practices and technology development. Weeds have become an important cause of rural poverty. Farmers have actively engaged in technology development and new labour practices have emerged. Officials early on did report weed problems, especially where export crops were concerned. Researchers have not translated the new weed problem into a research priority until very recently, resulting in limited and inappropriate weed management technologies. The challenge of the research of which this study is part is to optimize weed management, by combining emergent indigenous weed management practices with scientific knowledge.

The importance of seasonal variability and tactical responses to risk on estimating the economic benefits of integrated weed management

AbstractSeasonal variability is an important source of risk faced by farmers and, regardless of an individual's attitude to risk, there are options to tactically adjust production strategies as the outcomes of risk become known. The objective of this article is to measure the economic benefits of alternative approaches to managing weeds, one of the most serious production problems in Australian cropping systems. A bioeconomic model that combines weed biology, crop growth and economics is developed to value the effects of seasonal variability and the role of tactical responses and sequential decision making in determining an optimal integrated weed management strategy. This shows that there are substantial differences in the measured long‐term benefits from deterministic and stochastic simulations. It is concluded that, for research evaluation of technologies that involve complex biological and dynamic systems, ignoring the impacts of seasonal variability, responses to risk and sequential decision making can lead to an incorrect estimate of the economic benefits of a technology. In this case study of optimal weed management strategies in Australia, the size of the error is high.

A model for predicting invasive weed and grass dynamics. I. Model development

Invasive weed managers are presented with a complicated and ever-enlarging set of management alternatives. Identifying the optimal weed management strategy for a given set of conditions requires predicting how candidate strategies will affect plant community composition. Although field experiments have advanced our ability to predict postmanagement composition, extrapolation problems limit the prediction accuracy achieved by interpreting treatment means as predictions. Examples of extrapolation problems include nonlinear relationships between competing plants, site-to-site variation in plant population growth rates, and the carrying capacities of desired species and weeds. Our objective was to develop a model that improves predictions of weed management outcomes by overcoming a subset of these problems. To develop the model, we used data from two field experiments in which four Kentucky bluegrass, six western wheatgrass, and six invasive plant (i.e., leafy spurge) densities were combined in field plots. Graphs of our model's predictions vs. observed field experiment data indicate that the model predicted the data accurately. Our model may improve predictions of plant community response to invasive weed management actions.

Environmental weed control policy in Australia: current approaches, policy limitations and future directions

Plant invasions of natural systems threaten biodiversity and ecosystem processes across many biomes. Historically most plant invasions have been facilitated by human activities such as industry, transport and landscape modification. Consequently, both causes and management of weed invasion are dependent on human behaviour and management advice provided by ecologists needs to take account of this fact. This paper assesses current environmental weed control policy in Australia and asks: are government, land managers and the scientific community using available social levers to achieve optimal weed management? We do this by comparing aspects of weed policy with a generalized natural resource policy framework. Adequacy of issue characterization and policy framing are discussed with particular reference to public perceptions of the weed problem, policy scaling and defining policy principles and goals. The implementation of policy Instruments, including regulation, VOluntary incentives, education, Information, motivational instruments, property-right instruments and pricing mechanisms are reviewed. Limitations of current instruments and potential options to improve instrument effectiveness are discussed. Funding arrangements for environmental weed control are also reported: environmental weed invasion generally represents an external cost to economic markets which has resulted in relatively low funding levels for control operations. Finally, review and monitoring procedures in weed programmes and policy are addressed. Rigorous monitoring systems are important in effective, adaptive weed management where control techniques are continually refined to improve ecological outcomes. The utility of maintaining links between project outcomes and policy inputs along with methods of implementing appropriate monitoring are discussed.

Models for Improving the Targeting and Implementation of Biological Control of Weeds1

Abstract Managers are faced with considerable uncertainty about the systems they manage; yet, they are still expected to optimize weed management. A wide variety of mathematical models can be used to improve the efficacy and implementation of biocontrol for invasive plants. In this article, applied insights that have been generated by mathematical models of biological control systems are described. First, the ways in which models can be used to help choose appropriate agents for biocontrol are outlined. In particular, a novel example showing how demographic and dispersal models can be linked to address the life-history stage to target to reduce either local abundance or spatial spread of weeds is presented. Second, the use of stochastic optimization models to improve biological control release and redistribution strategies is reviewed. The discussion outlines the way in which learning about uncertainties can be explicitly included in the management process. These two topics demonstrate the use of ecologic...

Compensatory responses of late watergrass (Echinochloa phyllopogon) and rice to resource limitations

The development of optimal weed management strategies that rely, in part, on crop interference will require an understanding of how weeds compensate for limitations in above- and belowground resources. Trade-offs in the leaf morphology and biomass partitioning of rice and late watergrass were investigated under glasshouse conditions in 1999 and 2000. Both species responded to shade with increased height, reduced biomass, greater partitioning of biomass to leaves, and greater leaf area ratios. At the lowest light level (18% sunlight), plants of both species showed little response to nitrogen (N). However, height, tillers, biomass, and leaf area increased for plants grown at 50% and full sunlight as N increased from 0 to 224 kg N ha−1. Late watergrass exhibited more plasticity in specific leaf area and root weight ratio than rice in response to shade. This plasticity contributed to the ability of late watergrass to maintain a higher percent of its tillers and total dry weight than rice when sunlight was reduced by 50%. These results support the hypothesis that except at low light levels, limited N further reduces the growth of shaded late watergrass plants. Thus, weed management strategies that limit the plasticity of late watergrass by manipulating light and N availability are likely to be more effective than strategies that rely on manipulating a single resource.

WeedSOFT®: a weed management decision support system

WeedSOFT® is a decision support system that was developed to help farmers and consultants in Nebraska with the selection of optimal weed management strategies. WeedSOFT® evolved from HERB, a bioeconomic model for soybean that was developed in North Carolina. The program is composed of four independent modules, namely, ADVISOR, EnviroFX, MapVIEW, and WeedVIEW. ADVISOR helps the user select a treatment based on maximum yield or maximum net gain. EnviroFX and MapVIEW provide environmentally relevant herbicide information and county soil maps that indicate vulnerability to groundwater contamination. WeedVIEW is a visual library of color images and line drawings of 46 common weed species. Over 500 farmers and consultants in Nebraska and adjacent states use WeedSOFT®. As a result of the current regionalization effort, the user base is expected to increase rapidly during the next 2 or 3 yr. This article explains the algorithms implemented in the current version of WeedSOFT®.

Quantificação dos herbicidas glyphosate e sulfosate na água após simulação de chuva

A lavagem de herbicidas aplicados nas folhas das plantas é influenciada por características relacionadas com a planta e por fatores ambientais. Dentre os fatores ambientais, umidade do solo e precipitação pluvial podem interferir de forma significativa no desempenho desses produtos; assim, o conhecimento dessa interferência é fundamental para racionalização da aplicação de herbicidas no manejo das plantas daninhas. O objetivo deste trabalho foi quantificar resíduos dos herbicidas glyphosate e sulfosate na água, após aplicação foliar desses herbicidas e de 53 mm h-1 de chuva simulada sobre plantas de Brachiaria brizantha cultivadas em ausência e sob estresse hídrico. Utilizou-se neste estudo o tomateiro (Lycopersicon esculentum) 'Santa Clara' como planta-teste. O comprimento de raiz foi a característica mais sensível e também a mais adequada para evidenciar a resposta das plantas às doses dos herbicidas, e o tomateiro se mostrou mais sensível ao glyphosate do que ao sulfosate. Os valores de I50 para o glyphosate e o sulfosate obtidos nas curvas-padrão foram de 324,1 e 407,8 mg L-1, respectivamente, para o comprimento de raiz. O I50 foi menor quando os herbicidas foram aplicados em plantas sob estresse hídrico.

Apocynum cannabinumseed germination and vegetative shoot emergence

Apocynum cannabinumis a native creeping perennial distributed throughout the U.S., with increasing importance in reduced tillage systems throughout the Midwest.Apocynum cannabinumhas been shown to be a difficult species to control in field crops. Effective weed management is often a function of the timing of control practice. Knowledge of weed emergence patterns may be useful in predicting the optimum time of weed management. The objectives of these studies were to describe how temperature and moisture affectA. cannabinumseed germination and to describe the relationship between growing degree units (GDU) andA. cannabinumvegetative shoot emergence. At constant temperatures, seed germination was described as a sigmoidal function of temperature (r2= 0.83), with maximum germination (32%) from 26 to 34 C. Under alternating temperatures, seed germination increased in a linear relationship between mean temperatures of 15 and 34 C (r2= 0.85). Maximum seed germination (88%) occurred at a mean temperature of 34 C under alternating temperatures. The relationship between seed germination and osmotic potential between −1.0 and 0 MPa was described by a gompertz function (r2= 0.98). Germination at −1.0 MPa was 4% and increased in a near linear manner to the nontreated control (0 MPa), which had 80% germination. Vegetative shoot emergence in 1997 and 1998 had a sigmoidal relationship to GDU using a base temperature of 6 C (r2= 0.96). However, initial shoot appearance was not consistent over years, with first emergence recorded on May 21, 1997 (132 GDU), and May 5, 1998 (73 GDU). Approximately 50% of the shoots emerged before June 7, 1997 (282 GDU), and May 21, 1998 (285 GDU); therefore, optimal weed management programs will need to be initiated following this GDU accumulation.

Optimization of Weed Management Systems: The Role of Ecological Models of Interplant Competition

The strategy to optimize weed management systems with a minimum use of herbicides includes both the adaptation of crop management practices and well designed decision making systems, based on postemergence observations of weed infestations. Both strategies require thorough quantitative insight into the crop weed ecosystem, which can be provided by systems analysis, using process based models. These models also can be applied to similar systems like intercropping. For practical application, however, a simple measure of weed infestation and a simple model which relates weed infestation to yield loss are required. Recent progress in model development is discussed. An alternative empirical model that predicts yield loss from the relative leaf area of the weeds shortly after crop emergence, seems to be a useful approach for prediction of yield loss shortly after crop emergence. The use of systems approaches at different levels of detail for bridging the gap between research and practical application is discussed.