Economic Weed Threshold Research Articles

Precision Chemical Weed Management Strategies: A Review and a Design of a New CNN-Based Modular Spot Sprayer

Site-specific weed control offers a great potential for herbicide savings in agricultural crops without causing yield losses and additional weed management costs in the following years. Therefore, precision weed management is an efficient tool to meet the EU targets for pesticide reduction. This review summarizes different commercial technologies and prototypes for precision patch spraying and spot spraying. All the presented technologies have in common that they consist of three essential parts. (1) Sensors and classifiers for weed/crop detection, (2) Decision algorithms to decide whether weed control is needed and to determine a suitable type and rate of herbicide. Usually, decision algorithms are installed on a controller and (3) a precise sprayer with boom section control or single nozzle control. One point that differs between some of the techniques is the way the decision algorithms classify. They are based on different approaches. Green vegetation can be differentiated from soil and crop residues based on spectral information in the visible and near-infrared wavebands (“Green on Brown”). Those sensors can be applied for real-time on/off control of single nozzles to control weeds before sowing after conservation tillage and in the inter-row area of crops. More sophisticated imaging algorithms are used to classify weeds in crops (“Green on Green”). This paper will focus on Convolutional Neural Networks (CNN) for plant species identification. Alternatively, the position of each crop can be recorded during sowing/planting and afterward herbicides can be targeted to single weeds or larger patches of weeds if the economic weed threshold is exceeded. With a standardized protocol of data communication between sensor, controller and sprayer, the user can combine different sensors with different sprayers. In this review, an ISOBUS communication protocol is presented for a spot sprayer. Precision chemical weed control can be realized with tractor-mounted sprayers and autonomous robots. Commercial systems for both classes will be introduced and their economic and environmental benefits and limitations will be highlighted. Farmers ask for robust systems with less need for maintenance and flexible application in different crops.

ECONOMIC WEED THRESHOLD OF MARANTA SOBOLIFERA PLANTS IN OFF-SEASON CORN

Maranta sobolifera (Caetê) has tolerance to chemical management and has spread consistently on the agricultural areas of the western region of Paraná over the years. However, there is little information about its potential to interfere with the main agricultural crops. This study aimed to estimate the economic weed threshold (EWT) of M. sobolifera plants in commercial areas of production of off-season corn. There were losses in grain yield of up to 303.7 kg plant-1 of M. sobolifera. Considering an acceptable loss in grain yield of 614.05 kg ha-1, EWT estimates varied from 2.0 to 41.2 plants m-2 of M. sobolifera. In practice, these data can be used in no-till areas, where complementary control is necessary at the crop post-emergence (V4-V6), after desiccation of the area, to maintain weed density at tolerable levels until the end of the cycle. In addition, factors such as the use of less competitive hybrids, obtaining the maximum productive potential of the crop, increasing the value of the harvested product and the efficiency of chemical management (desiccation) and a reduction in the cost of control contribute to the reduction of the EWT and make the adoption of management practices of M. sobolifera more profitable in off-season corn.

Additive design: the concept and data analysis

SummaryCrop–weed competition is extensively studied in weed science. The additive design, in which weed density varies and the crop density is kept constant, is the most commonly utilised design in plant competition studies. The additive design is important to calculate economic weed thresholds and improve weed control decision‐making. Crop–weed competition studies are usually conducted by weed scientists, who sometimes report misleading conclusions because of lack of statistical knowledge needed for data analysis of such studies. Therefore, the objective of this manuscript is to provide the concept of additive design and demonstrate the model selection approach for describing crop–weed density relationship to non‐statisticians. We evaluated three models routinely used in the literature to interpret data from additive designs, including polynomial quadratic, sigmoid and rectangular hyperbola curves. Based on the described statistical criteria, we demonstrated the rectangular hyperbola to be the most appropriate model to describe data from an additive design study looking at Richardia brasiliensis and Commelina benghalensis competition with maize (Zea mays). Moreover, we describe step‐by‐step how to perform the statistical analysis in R software and interpret the results of crop–weed competition studies. We suggest the use of the rectangular hyperbola as a standardised model for crop–weed competition in additive design.

친환경 고추밭 바랭이와 가는털비름 발생밀도에 따른 고추 수량 반응

This study was conducted to predict the yield response of red pepper and to determine the economic weed threshold levels for red pepper cultivation field from competition with the most serious weeds, Amaranthus patulus and Digitaria ciliaris in Youngyang of Korea. Crop yield as a function of weed density was predicted by using a rectangular hyperbola, and their economic threshold levels were determined by using the equation developed by (1987). The red pepper yield loss models of weeds were predicted as y=304.7/(1+0.063x), R 2 =0.967 in D. ciliaris and y=281.3/(1+0.1723x), R 2 =0.952 in A. patulus. Economic thresholds calculated using Cousens equation were negatively related with the competitiveness of weed. Economic thresholds of each weed were calculated as 18.2 plant 100m -2 in D ciliaris, and 7.2 plant 100 m -2 in A. patulus.

고추밭 잡초 피와 명아주 발생밀도에 따른 경합 및 고추 수량 감소

본 시험은 2010년에 경상북도 농업기술원 영양고추시험장 고추 재배포장에서 밭 잡초로 가장 문제시 되고 있는 잡초 중 피와 명아주를 대상으로 잡초 밀도별 고추와의 경합력을 구명하고 rectangular hyperbola 모델을 기초로 잡초의 밀도에 따른 건고추수량 감소를 예측하여 경제적인 방제 필요수준을 구명하고자 실시하였다. 잡초를 완전 방제 했을 경우를 가상한 건고추 수량은 명아주에서 10a당 323.2kg으로 피의 317.0kg 보다 다소 높았으며, 고추와 잡초의 경합력은 명아주에서 0.29으로 피의 0.1707 보다 높았고, 수량 예측식은 명아주가 y=323.2kg/(1+0.29x), <TEX>$R^2$</TEX>=0.896, 피가 y=317.0kg/(1+0.1707x), <TEX>$R^2$</TEX>=0.895로 나타났다. 제초제 구입 비용을 10a당 6,500원, 제초제 살포 인건비를 20,000원, 건고추의 가격을 kg당 8,000원, 제초제 방제가 95%로 적용하여 구한 경제적 피해 한계 밀도는 잡초 완전 방제시 수량이 10a당 323.2kg이고 잡초 1본당 수량 감수 정도가 0.29인 명아주는 <TEX>$100m^2$</TEX>당 3.7본, 잡초 완전 방제시 수량이 317.0kg이고 잡초 1본당 수량 감수 정도가 0.1707인 피는 <TEX>$100m^2$</TEX>당 6.5본이었다. This study was conducted to predict the yield loss of red pepper and to determine the economic weed thresholds levels for red pepper cultivation field from competition with the most serious weeds, Echinochlor crus-galli (L.) P. beauv. (barnyard grass) and Chenopodium album L. (goosefoot) in Youngyang of Korea. Crop yield as a function of weed density was predicted by using a rectangular hyperbola, and their economic threshold levels were determined by using the equation developed by Cousens (1987). The red pepper yield loss models of weeds were predicted as y=317.0 kg/ (1+0.1707x), <TEX>$R^2$</TEX>=0.895 in E. crus-galli and y=323.2 kg/(1+0.2900x), <TEX>$R^2$</TEX>=0.896 in C. album L.. Economic thresholds calculated using Cousens' equation was negatively related with the competitiveness of weed. Economic thresholds of each weed were calculated as 6.5 plant <TEX>$100m^{-2}$</TEX> in E. crus-galli, and 3.7 plant <TEX>$100m^{-2}$</TEX> in C. album L..

Interferência e nível de dano econômico de Brachiaria plantaginea e Ipomoea nil na cultura do feijão comum

As pesquisas acerca do impacto da interferência das plantas daninhas sobre as culturas normalmente são realizadas com uma única espécie infestante, quando na realidade podem ocorrer diversas. Os objetivos deste trabalho foram avaliar a interferência de Brachiaria plantaginea e Ipomoea nil sobre o rendimento de grãos do feijoeiro (Phaseolus vulgaris) e determinar o nível de dano econômico (NDE) de cada espécie na cultura. Foram realizados dois experimentos a campo com as cultivares de feijão 'IPR Graúna' (Grupo Preto) e 'UTF-06' (Grupo Carioca) em convivência com infestações mistas em diferentes proporções aleatórias das espécies B. plantaginea e I. nil. Modelos de regressão múltiplos foram utilizados para determinar a capacidade de interferência de cada espécie daninha sobre a produtividade da cultura. O impacto de interferência de cada planta de I. nil correspondeu a 2,6 e 0,25 quando comparada a cada planta de B. plantaginea, dependente das proporções relativas na comunidade infestante e das condições de cada experimento. A cultivar 'IPR Graúna' apresentou maior habilidade competitiva do que 'UTF-06'. O NDE foi dependente da proporção relativa de cada espécie daninha na comunidade e foi obtido sob baixas infestações (&lt;16 plantas m-2) em todas as condições testadas e simuladas.

Multispecies weed competition and their economic threshold on the wheat crop

Two field experiments were conducted to evaluate the effects of multispecies weed competition on wheat grain yield and to determine their economic threshold on the crop. The experiments were conducted in 2002, on two sites in Iran: at the Agricultural Research Station on Ferdowsi University of Mashhad (E1) and on the fields of Shirvan's Agricultural College (E2). A 15 x 50 m area of a 15 ha wheat field in E1 and a 15 x 50 m area of a 28 ha wheat field in E2 were selected as experimental sites. These areas were managed like other parts of the fields, except for the use of herbicides. At the beginning of the shooting stage, 30 points were randomly selected by dropping a 50 x 50 cm square marker on each site. The weeds present in E1 were: Avena ludoviciana, Chenopodium album, Solanum nigrum, Stellaria holostea, Convolvulus spp., Fumaria spp., Sonchus spp., and Polygonum aviculare. In E2 the weeds were A. ludoviciana, Erysimum sp., P. aviculare, Rapistrum rugosum, C. album, Salsola kali, and Sonchus sp. The data obtained within the sampled squares were submitted to regression equations and weeds densities were calculated in terms of TCL (Total Competitive Load). The regression analysis model indicated that only A. ludoviciana, Convolvulus spp. and C. album, in E1; and A. ludoviciana, S. kali, and R. rugosum, in E2 had a significant effect on the wheat yield reduction. Weed economic thresholds were 5.23 TCL in E1 and 6.16 TCL in E2; which were equivalent to 5 plants m-2 of A. ludoviciana or 12 plants m-2 of Convolvulus spp. or 19 plants m-2 of C. album in E1; and 6 plants m-2 A. ludoviciana, 13 plants m-2 S. kali and 27 plants m-2 R. rugosum in E2. Simulations of economic weed thresholds using several wheat grain prices and weed control costs allowed a better comparison of the experiments, suggesting that a more competitive crop at location E1 than at E2 was the cause of a lower weed competitive ability at the first location.

Interferência e nível de dano econômico de capim-arroz sobre o arroz em função do arranjo de plantas da cultura

Na cultura do arroz irrigado ocorrem elevadas perdas de produtividade de grãos devido à interferência de plantas daninhas, pois estas também estão adaptadas ao ambiente inundado de cultivo do cereal. Objetivou-se avaliar a interferência e determinar o nível de dano econômico de populações de capim-arroz em arroz irrigado em função do arranjo de plantas da cultura. Foi realizado um experimento em campo, com cultivo de arroz em sistema convencional. Os tratamentos foram constituídos por três arranjos de plantas de arroz, cultivar BRS Pelota (17 e 32 cm e semeadura a lanço), e nove populações de capim-arroz em cada método de semeadura. O modelo de regressão não linear da hipérbole retangular estima adequadamente as perdas de produtividade do arroz irrigado na presença de plantas de capim-arroz. A cultura do arroz semeada a lanço apresenta maior habilidade competitiva com o capim-arroz em relação à semeadura em linha nos espaçamentos de 17 e 32 cm. A variável área foliar apresenta melhor ajuste ao modelo da hipérbole retangular, comparativamente às variáveis população de plantas, massa seca da parte aérea e cobertura do solo. A utilização de semeadura a lanço aumenta o nível de dano econômico, justificando a adoção de medidas de controle do capim-arroz em níveis mais elevados de população. Acréscimo na produtividade de grãos, no preço do arroz e na eficiência do herbicida e redução no custo de controle diminuem os valores do nível de dano econômico, justificando a adoção de medidas de controle em baixas populações de capim-arroz.

Precision farming for weed management: techniques

Site-specific weed control techniques have gained interest in the precision farming community over the last years. Managing weeds on a subfield level requires measuring the varying density of weeds within a field. Decision models aid in the selection and adjustment of the treatments, depending on the weed infestation. The weed control can be done either with herbicides or mechanically. A site-specific herbicide application technology can save large amounts of herbicides. Mechanical weed control techniques adapting to the weed situation in the field are applicable to a wide spectrum of crops. Site-specific techniques for the detection and management of weeds are presented. A system for the discrimination of different weed species and crops from images is described, which generates weed maps automatically. Models for the yield effect of weeds are developed and applied in on-farm-research experimental setups. Economic weed thresholds are derived and used for a herbicide application with a patch sprayer.

Níveis de dano econômico para decisão de controle de capim-arroz (Echinochloa spp.) em arroz irrigado (Oryza sativa)

O nível de dano econômico (NDE) para monitoramento das infestações de capim-arroz em lavouras de arroz irrigado permite adotar medidas de manejo na cultura e usar herbicidas de maneira racional. Objetivou-se com o trabalho determinar NDE para capim-arroz, presente em lavouras de arroz irrigado, calculado na base de um único ano, em função de populações de capim-arroz, de cultivares de arroz e de épocas de entrada de água na lavoura. Para isso, foram conduzidos dois experimentos em delineamento experimental completamente casualizado, sem repetição. No primeiro experimento, os tratamentos foram constituídos de seis cultivares de arroz: BRS-Atalanta e IRGA 421 (ciclo muito curto), IRGA 416, IRGA 417 e Avaxi (ciclo curto) e BRS-Fronteira (ciclo médio); e dez populações de capim-arroz. No segundo experimento usaram-se como tratamentos épocas de início da irrigação: 1, 10 e 20 dias após aplicação dos tratamentos herbicidas (DAT); e populações de capim-arroz. Os NDEs estimados para o capim-arroz variaram em função das práticas de manejo adotadas na cultura do arroz irrigado. Os NDEs estimados para os cultivares de arroz IRGA 416 e 417 foram superiores aos dos demais cultivares quando em competição com capim-arroz. O atraso da entrada de água diminui os NDEs para o cultivar de arroz BRS-Pelota. Aumentos nas perdas de produtividade por unidade de planta daninha, no potencial de produtividade da cultura, no valor do produto colhido e na eficiência do herbicida e diminuição do custo de controle reduziram os NDEs, tornando econômica a adoção de práticas de manejo sob baixas populações de capim-arroz em competição com arroz irrigado.

Reconciling the conservation of in-field biodiversity with crop production using a simulation model of weed growth and competition

The conservation of biodiversity within cropped fields, through tolerating low weed populations, would complement un-cropped wildlife refuges and increase the functional diversity of the farmed landscape. These benefits need to be balanced with the risk of lost crop production from weed competition. A simulation model of weed growth and competition was developed and parameterised for 15 autumn germinating weed species common in UK winter wheat fields. The model was validated over 2 years and used to explore possible management options for reconciling the conservation of in-field biodiversity with winter wheat production. The model successfully predicted biomass production and crop yield loss from weed populations sown in two growing seasons. The predicted outcome of weed competition was highly dependent on weather, particularly the period of over winter growth. The model allows the risk associated with the economic weed threshold approach to be effectively managed—providing the control of less competitive broad leaf weeds is delayed until the spring. There were large differences in the model parameters between the species and the hypothesis that weed growth and competition could be modelled on the level of weed functional group was rejected.

Nível de dano econômico de Brachiaria plantaginea na cultura de milho irrigado

O nível de dano econômico (NDE) consiste na quantidade de plantas daninhas que causa impacto no rendimento de grãos da cultura que justifique o custo de seu controle. Os objetivos deste trabalho foram avaliar a possibilidade de utilizar experimentos de eficácia de herbicidas residuais para determinar o NDE, a partir do rendimento de grãos em relação à densidade de plantas de Brachiaria plantaginea (BRAPL) que emergem após o tratamento, e avaliar o impacto do preço da cultura e do custo do controle no NDE. A densidade de BRAPL foi determinada em um experimento no qual se realizaram tratamentos químicos que possibilitaram a emergência de diferentes quantidades de plantas e, em conseqüência, vários níveis de interferência sobre a cultura do milho. A avaliação da densidade foi feita aos 10, 20, 30, 40 e 50 dias após a emergência (DAE), de forma a abranger o período crítico de prevenção da interferência. Ao final do experimento foi avaliado o rendimento de grãos da cultura do milho. A resposta da regressão entre densidade de BRAPL e rendimento de grãos de milho ajustou curvas do tipo exponencial decrescente nas avaliações realizadas aos 10 e 20 DAE e curvas do tipo logístico (sigmoidal) aos 30, 40 e 50 DAE. O NDE de BRAPL em milho, com base na densidade determinada no início do período crítico de prevenção da interferência (20 DAE), considerando nível de produtividade de 10 t ha-1, variou entre 0,2 e 2,0 plantas m-2, dependendo do preço do milho e do custo do controle. O NDE determinado ao término do período crítico de interferência (50 DAE) correspondeu às densidades de BRAPL de 1,5 a 13 plantas m-2. Conclui-se que o NDE de BRAPL na cultura de milho pode ser estabelecido com dados de densidade desta espécie, determinados em experimentos para testes de herbicidas residuais. Assim, o NDE previsto será adequado para situações em que se deseja decidir por aplicações de herbicidas em pós-emergência em áreas onde foram aspergidos herbicidas residuais. Conclui-se, também, que o NDE de BRAPL em milho aumenta à medida que o preço da cultura diminui e o custo do controle aumenta e que o aumento do preço de grãos reduz o impacto do custo do controle de BRAPL no retorno econômico da cultura.

Real‐time weed detection, decision making and patch spraying in maize, sugarbeet, winter wheat and winter barley

SummaryInformation on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Most of all, it allows a potential reduction in herbicide use, when post‐emergence herbicides are only applied to field sections with weed infestation levels higher than the economic weed threshold; a review of such work is provided. This paper presents a system for site‐specific weed control in sugarbeet (Beta vulgaris L.), maize (Zea mays L.), winter wheat (Triticum aestivum L.) and winter barley (Hordeum vulgare L.), including online weed detection using digital image analysis, computer‐based decision making and global positioning systems (GPS)‐controlled patch spraying. In a 4‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 60% for herbicides against broad‐leaved weeds and 90% for grass weed herbicides. In sugarbeet and maize, average savings for grass weed herbicides were 78% in maize and 36% in sugarbeet. For herbicides against broad‐leaved weeds, 11% were saved in maize and 41% in sugarbeet.

Grower Acceptance of Economic Thresholds for Weed Management in Illinois

Although economic thresholds are often used to make insect control decisions, the use of thresholds for weed management has been limited. Surveys of growers, agricultural chemical dealers, and farm managers/rural appraisers helped identify limitations to grower acceptance of economic thresholds for weed management. Most growers were concerned about harvest problems due to weeds, with 64% identifying this factor as a major limitation. Landlord perception and weed seed production were identified by 38% of the growers as major limitations, while 36% of the growers listed general appearance of the field as reasons. In contrast, 75% of the agricultural chemical dealers and 63% of the farm managers surveyed listed field appearance as a major reason limiting grower acceptance of economic thresholds for weed management. Since grower concerns involve risk management and future profitability, economic weed thresholds that address long-term costs and benefits of weed control decisions may be more fully accepted.

Site Specific Weed Control in Winter Wheat

AbstractField experiments were conducted in two winter wheat fields to assess weed control and quantify the amount of herbicide applied with a GIS map‐based patch sprayer. Site specific weed management decisions were based on previously acquired weed distribution maps and an economic weed threshold model. A weed treatment map (on‐off) was generated and georeferenced to control the sprayer. A global positioning system was used to locate the sprayer in the field. In both fields, Alopecurus myos‐uroides was observed at low infestation levels, Galium aparine at medium infestation levels and the mean density for other broadleaf species exceeded 40 weed seedlings va‐ in both fields. Herbicide application was recommended for 58.3% of the first field and 54.6% of the second field. With the patch sprayer used for this study, 21% less herbicides were sprayed compared to an uniform broadcast application. Additional assessments of weed density in the first field 3 and 6 weeks after site specific weed control showed that almost the entire field was weed free. The results of this study demonstrated that site specific weed control was technically feasible but further investigations are needed to verify and evaluate site specific weed control methods.

Modellversuch zur Beschreibung von Konkurrenzvorgängen zwischen Sommerweizen und einer aus Capsella bursa‐pastoris L., Stellaria media L. und Alopecurus myosuroides Huds. bestehenden Mischverunkrautung

Abstract Investigation to Describe the Competition between Spring Wheat and a Weed Population Consisting of Capsella bursa‐pastoris L., Stellaria media L. and Alopecurus myosuroides Huds. When controlling weeds in cereals using economic threshold as criteria, weed populations must be evaluated for their potential to cause damage at a very early stage. As well as information of actual weed density or weed ground cover, further knowledge about the species specific growth and competition between weed populations is important.For this purpose the growth and competition between the weeds Capsella bursa‐pastoris L., Stellaria media L., Alopecurus myosuroides Huds. and spring wheat (Triticum aestivum L.) as a model of a typical weed mixture in cereals were studied in a container experiment. The growth with time of individual species was documented using true colour image processing. In that these measurements are non‐invasive, the system lends itself specially to time‐dependent analyses. The increasing amount of ground covered by leaves between two observation times served as a parameter to evaluate the increase in biomass over this time period and could be used as a evaluation of the competitiveness of the weed species studied.The results can be summarized as follows: 1) Stellaria media L. proved to be the most competitive of the studied species. 2) The competition to spring wheat from each weed species was similar. 3) A multi species weed population had a tendenci to a lower competitiveness to spring wheat, than a weed population of only‐one species.The importance of this and other similar studies for the improvement for the prediction of economic weed thresholds to estimate weed populations in early stages will be indicated.

Future Outlook for Herbicide-Resistance Research

Management of herbicide resistance will require interdisciplinary research to understand the mechanisms and dynamics of resistance. We believe that models are valuable tools. Models propose hypotheses about biological processes that influence the evolution of resistance and management tools that may reduce resistance in weed populations. Hypotheses help to direct research. For example, our model proposes that fitness and gene flow dramatically influence the evolution of and recovery from resistance in weed populations. Therefore, our research agenda should include ecological investigations of the life-history traits involved in fitness and gene flow. The model suggests thresholds of susceptible weed abundance to reduce selection pressure and to delay resistance. These thresholds will be related closely to economic weed thresholds. While the resistance issue emphasizes the need for basic biological and ecological research, resistance is only a part of the broader research agenda, which calls for holistic and interdisciplinary approaches to understanding and managing crop systems.