Control Of Soybean Rust Research Articles

Fungicide sensitivity and monocyclic parameters related to the Phakopsora pachyrhizi–soybean pathosystem from organic and conventional soybean production systems

The failure of chemical control of soybean rust has been related to the selection of less sensitive isolates, and the infection capacity of such isolates could have implications for the management of the disease. The aims of the present study were to compare the sensitivity to tebuconazole and azoxystrobin and the monocycle of soybean rust using isolates of Phakopsora pachyrhizi from two soybean fields with different production systems (organic and conventional) in 2012/13 and 2013/14 seasons, and to monitor mutations in the CYP51 gene. To assess the sensitivity to tebuconazole and azoxystrobin, detached leaf tests and in vitro germination, respectively, were used. To evaluate the monocycle, detached leaves were inoculated with a urediniospore suspension and evaluated daily by counting the number of uredia. The occurrence of the mutations in CYP51 was investigated by a pyrosequencing assay. In both 2012/13 and 2013/14 seasons, the EC50 to tebuconazole was lower for the population from the organic system (0.41 and 0.10 μg mL−1, respectively) compared to the conventional system (1.60 and 4.44 μg mL−1, respectively), while the EC50 to azoxystrobin was similar for both populations. The lower sensitivity to tebuconazole and azoxystrobin was associated with F120L + Y131H mutations in CYP51, and the F129L mutation in CYTB, respectively. The monomolecular model fitted to monocycle data and parameters related to the maximum asymptote and the AUDPC were superior for organic than the conventional system.

Meta-Analytic Modeling of the Decline in Performance of Fungicides for Managing Soybean Rust after a Decade of Use in Brazil.

An apparent decline of fungicide performance for the control of soybean rust in Brazil has been reported but the rate at which it has occurred has not been formally quantified. Control efficacy and yield response to three fungicides applied as single active ingredients (a.i.)-azoxystrobin (AZOX), cyproconazole (CYPR), and tebuconazole (TEBU)-and four applied as mixtures-AZOX+CYPR, picoxystrobin + CYPR, pyraclostrobin + epoxiconazole, and trifloxystrobin + prothioconazole (TRIF+PROT)-were summarized using network meta-analytic models fitted to mean severity and yield data from 250 trials (10-year period). The effect of year was tested on both variables in a meta-regression model. Overall control efficacy ranged from 56 to 84%; the three single-a.i. fungicides performed the poorest (56 to 62%). Yield increase for single-a.i. fungicides was as low as 30% but ranged from 47 to 65% for the premixes. Significant declines in both variables were detected for all fungicides except TRIF+PROT. For TEBU, control efficacy (yield response) declined the most: 78% (18%) to 54% (8%) from 2004-05 to 2013-14. The recent surge of resistant populations of Phakopsora pachyrhizi to both demethylation inhibitor and quinone outside inhibitor fungicides is likely the driving force behind a significant decline after 4 years of fungicide use.

SPRAY NOZZLES PERFORMANCE IN FUNGICIDES APPLICATIONS FOR ASIAN SOYBEAN RUST CONTROL

ABSTRACT: The performance of fungicides in controlling Asian soybean rust depends, in part, the spray quality of these products. The market of components to spray offers new types of nozzles which generate droplets with different characteristics. This study aimed to verify whether applications of fungicides with different spray nozzles interfere in soybean rust control. The experiment was conducted in the 2013/2014 harvest. The experimental design was a randomized block with three replications, and compared ten spray nozzles and a control without fungicide application. The applications were made with a backpack sprayer pressurized with CO2, set to apply a spray volume of 150 L ha-1. For the determination of severity four plants per plot were sampled, quantifying in each leaflet the number of uredinia cm-2, which permitted to integrate the area under the disease progress curve (AUDPC). We concluded that HYPRO GUARDIAN® 120015 Single pre orifice flat spray nozzle, that generates medium size of droplets, provided the lowest AUDPC of soybean rust, as well as the use of fungicide reflected in grain yield, which was on average 288% higher than that obtained by the control without fungicide application.

Use of a Canopy Opener in Fungicide Applications to Improve Asian Soybean Rust Control

Abstract. In soybeans, the leaves of the upper canopy often act as a shield against fungicide penetration, preventing pesticide deposition on target. Fungicide applications to control Asian soybean rust (ASR) are especially difficult because the infection usually starts on the lower canopy. In this study, soybean plants of an early indeterminate cultivar and a determinate cultivar were sprayed with the fungicide azoxystrobin + benzovindiflupyr at six different times of the day with or without the addition of a curtain of chains on the spray boom, which acted as a canopy opener. The number of uredia of cm-2 and grain yield were measured to evaluate application efficacy. We found that the use of the curtain of chains reduced ASR control on the upper canopy for the indeterminate cultivar; however, less of a negative effect was observed for the determinate cultivar. The curtain of chains improved ASR control on the lower and middle canopies at more hours of the day for the determinate cultivar. For both cultivars, the curtain of chains increased ASR control at 6:00, 9:00, and 18:00 h on the lower canopy. Grain yield was also higher with the curtain of chains at 6:00 and 9:00 h for the determinate cultivar. Our results showed that using the curtain of chains could improve fungicide droplet deposition on the lower canopy, leading to greater ASR control and possibly increasing yield. However, it is important to consider the plant architecture and hour of application to maximize the benefit of the curtain of chains. Keywords: Canopy opener, Fungicide penetration, Phakopsora pachyrhizi, Plant architecture, Spray deposition.

Effect of the interaction between fungicide application time and rainfall simulation interval on Asian Soybean Rust control effectiveness

Environmental factors affect the performance of fungicides in soybean (Glycine max (L.) Merr.). They also influence the residual activity of the products applied to the leaves. The objective of this study was to assess the control effectiveness of the interaction between fungicide application and rainfall simulation on Asian Soybean Rust (ASR). Two experiments were conducted, one in the greenhouse, in a completely randomized design, and the other in the field, in a randomized block design. Both the experiments had the same factorial arrangement of 6x5, with four replications. Factor A: Five fungicide applications time at 0400 h, 0900 h, 1400 h, 1800 h, 2300 h and, a control with no application; Factor B: four intervals of time between the application of fungicide and rainfall simulation at 0, 30, 60 and 120 min for the experiment in the greenhouse and at 2, 30, 60, 120 min for the experiment in the field. A control was included for both the experiments with no rainfall. The number of days to the appearance of the first pustules was determined, along with severity of ASR, relative chlorophyll index and productivity. It was found that the ASR control effectiveness of fungicide applications in soybean plants in sunlight was less efficient with rainfall simulation. The rainfall simulation had greater negative effect on disease control effectiveness in applications conducted at night under dew conditions. The application conducted at 0900 h showed the greatest disease control effectiveness in both greenhouse and in the field conditions. The 1400 h application showed decreased fungicide control residual and ASR control effectiveness, possibly due to a combination of the low relative humidity and high temperature. Rainfall simulation carried out at 120 min after application still had the ability to affect the ASR control effectiveness.

Curative and eradicant action of fungicides to control Phakopsora pachyrhizi in soybean plants

ABSTRACT Experiments were carried out in a growth chamber and laboratory to quantify the curative and eradicant actions of fungicides in Asian soybean rust control. The experiments were conducted with the CD 214 RR cultivar, assessing the following fungicides, separately or in association, chlorothalonil, flutriafol, cyproconazole + trifloxystrobin, epoxiconazole + pyraclostrobin, cyproconazole + azoxystrobin, and cyproconazole + picoxystrobin. The fungicides were applied at four (curative) and nine days after inoculation (eradicant treatment). Treatments were evaluated according to the density of lesions and uredia/cm2, and the eradicant treatment was assessed based on the necrosis of lesions/uredia and on uredospore viability. Except for the fungicide chlorothalonil, there was curative action of latent/virtual infections by the fungicides. Penetrant fungicides that are absorbed have curative and eradicant action to soybean rust.

FLUXAPYROXAD IN THE ASIAN SOYBEAN RUST CONTROL IN THE CERRADO BIOME

ABSTRACT The etiologic agent of the Asian soybean rust is the Phakopsora pachyrhizi, which causes a reduction in the photosynthetic leaf area and, consequently, in the crop yield. Chemical control is one of the main measures for its management. The objective of this work was to evaluate the efficacy and selectivity of the fluxapyroxad fungicide on controlling the Asian soybean rust, under the edaphoclimatic conditions of the Cerrado biome. The experiment was conducted in an area under no-tillage system, in the Agricultural Research Center, Rio Verde, Goias, Brazil, during the 2012/2013 crop season, using the cultivar NA7337. A randomized block experimental design was used, with twelve treatments and four replications. The treatments consisted of applications of fluxapyroxad (FX), pyraclostrobin (PT), epoxiconazole (EX) and metconazole (MZ). The average severity of the disease in the plants reached 37% in the Control. All treatments with fungicides differed from the Control. Treatments 9, 10, 11 and 12 provided the greatest rates of soybean rust control. The treatments 10, 11 and 12 had the highest thousand grain weights, and the yields of the treatments 2, 3 and 11, despite higher than the Control, were lower than the treatments 4, 5, 6, 7, 8, 9, 10 and 12, which had statistically equal yields. The increasing in yield, compared to the Control, ranged from 10.05% (pyraclostrobin, epoxiconazole + pyraclostrobin + mineral oil) to 30.55% (pyraclostrobin, pyraclostrobin + fluxapyroxad + mineral oil and pyraclostrobin + metconazole + mineral oil). The highest rates of soybean rust control were presented by fungicides containing fluxapyroxad.

Pontas de pulverização e horários de aplicação no controle químico de ferrugem asiática da soja

Spray nozzles were evaluated at two different spraying times (14h and 17h 30m), in Mato Grosso do Sul, Brazil regarding Asian soybean rust control ( Phakopsora pachyrhizi Sidow). Four spray nozzles were evaluated: deflector plain tips, double deflector plain tips, extended range flat spray tips and double plain tips. A commercial formulation of epoxiconazole and pyraclostrobin (0,5 L ha-1) was sprayed in the plots. Soybean leaves were collected at the top, middle and lower canopy, for assessment of the number of lesions and uredinias. In addition, leaf area affected by P. pachyrhizi was estimated . Plots sprayed with double deflector plain tips had lower uredinia counts in the lower canopy compared to the other tips tested. Sprays done early in the afternoon with double deflector plain nozzles had lower uredinia counts compared to the other treatments. Smaller defoliation and greater a-thousand grain mass were detected in plots sprayed with fungicide using a double deflector plain tip compared to the deflector plain nozzle. Soybean yield was not affected by nozzles and time of fungicide spray.

Sensitivity of Phakopsora pachyrhizi towards quinone‐outside‐inhibitors and demethylation‐inhibitors, and corresponding resistance mechanisms

Since the invasion of Phakopsora pachyrhizi (Syd. & P. Syd.) in Brazil, there have been detrimental yield losses of soybeans [Glycine max (L.) Merr.]. Disease management is mainly based on fungicide treatment. The sensitivity of single P. pachyhrizi isolates towards different demethylation-inhibitors (DMIs) and quinone-outside-inhibitors (QoI) was surveyed and the corresponding resistance mechanisms were analysed. The QoI-response remained stable, while a loss of sensitivity towards DMIs occurred. Molecular analyses of cytochrome b showed an intron after codon 143 which is reported to prevent the development of a G143A mutation. Analysis of cyp51 revealed that point mutations and overexpression are involved in the sensitivity reduction towards DMIs. Of the detected mutations, Y131F and Y131H, respectively, and K142R are likely homologous to mutations found in other pathogens. As suggested by modelling studies, these three mutations as well as additional mutations F120L, I145F and I475T correlate to increased effective doses of 50%, ED50 -values, towards all tested DMIs. Furthermore, a constitutive up-regulation of the cyp51-gene up to ten-fold was noticed in some of the DMI-adapted isolates, while all sensitive isolates responded as the wild type. The G143A mutation is thought to result in significant as well as stable resistance factors towards QoIs, while other mutations play only a minor role. Since G143A development is prevented in Phakopsora pachyhrizi, a stable control of soybean rust with QoIs in future is rather likely. In contrast, a shifting in sensitivity towards DMIs has been observed, which is due to multiple independent mechanisms.

Espectros de gotas e idade de trifólios e sua interação com a área abaixo da curva de progresso da ferrugem da soja

O objetivo do presente trabalho foi avaliar o efeito de espectros de gotas (grossas, médias e finas) na velocidade de absorção de fungicidas, para trifólios de diferentes idades, através de medida indireta expressa pelo residual de controle de ferrugem asiática da soja (Phakopsora pachyrhizi). O delineamento experimental utilizado foi inteiramente casualizado, com quatro repetições, em arranjo fatorial (3x3x5x4), cujos fatores foram compostos por: três espectros de gotas (grossas, médias e finas); três idades fisiológicas de trifólios na planta (1°, 3° e 5° trifólios); quatro períodos de tempo entre a aplicação de fungicidas e chuva simulada (0, 30, 60 e 120min.), mais uma testemunha sem chuva; três tratamentos com fungicida: azoxistrobina + ciproconazol (60+24g i.a. ha-1) + óleo mineral 0,6L ha-1, azoxistrobina (50g i.a. ha-1) + óleo mineral 0,6L ha-1 e ciproconazol (30g i.a. ha-1), mais uma testemunha sem aplicação. Avaliou-se densidade de gotas por centímetro quadrado, diâmetro mediano volumétrico, diâmetro mediano numérico, amplitude relativa, número de dias para o aparecimento da primeira pústula e a área abaixo da curva de progresso da doença. Verificou-se que gotas de menor DMV proporcionam maior velocidade de absorção de fungicidas. Trifólios mais novos absorvem os fungicidas mais rapidamente. A utilização da mistura de azoxistrobina + ciproconazol proporcionou menor evolução da doença com consequente menor área abaixo da curva de progresso da doença.

Effects of Silicon Applications on Soybean Rust Development Under Greenhouse and Field Conditions.

Soybean rust (SBR), caused by Phakopsora pachyrhizi, is one of the most destructive fungal diseases affecting soybean production. Silicon (Si) amendments were studied as an alternative strategy to control SBR because this element was reported to suppress a number of plant diseases in other host-pathogen systems. In greenhouse experiments, soybean cultivars inoculated with P. pachyrhizi received soil applications of wollastonite (CaSiO3) (Si at 0, 0.96, and 1.92 t ha-1) or foliar applications of potassium silicate (K2SiO3) (Si at 0, 500, 1,000, or 2,000 mg kg-1). Greenhouse experiment results demonstrated that Si treatments delayed disease onset by approximately 3 days. The area under disease progress curve (AUDPC) of plants receiving Si treatments also was significantly lower than the AUDPC of non-Si-treated plants. For field experiments, an average 3-day delay in disease onset was observed only for soil Si treatments. Reductions in AUDPC of up to 43 and 36% were also observed for soil and foliar Si treatments, respectively. Considering the natural delayed disease onset due to the inability of the pathogen to overwinter in the major soybean production areas of the United States, the delay in disease onset and the final reduction in AUDPC observed by the soil Si treatments used may lead to the development of SBR control practices that can benefit organic and conventional soybean production systems.

Systems of aerial spraying for soybean rust control

The soybean rust caused by Phakopsora pachyrhizi is considered the main soybean disease and consequently the appropriate selection and the use of spraying equipment are vital for its control. The aim of this study was to evaluate the performance of aerial application equipment for soybean rust control. It was used: Micronair AU 5000 at 10 L ha-1 (with oil) and at 20 L ha-1 (without oil); Stol ARD atomizer at 10 and 20 L ha-1 (both with oil) and Spectrum (electrostatic) at 10 L ha-1 (without oil). The adjuvant was cotton oil (1.0 L ha-1) with emulsifier (BR 455) at 0.025 L ha-1. The field trial was set up at the 3rd fungicide application, when f four replications of each treatment. There were no statistical differences among treatments related to fungicide deposits by at a Confidence Interval of 95%. It was observed that the best results were obtained with Micronair (10 L ha-1 with oil), Stol (20 L ha-1 with oil) and electrostatic system at 10 L ha-1 with the lowest relative humidity (64%).

Assistência de ar em barra de pulverização no controle da ferrugem asiática da soja

O experimento foi instalado em Botucatu, na cultura da soja, safra 2006/2007. Duas tecnologias de aplicação foram comparadas: pulverização convencional (sem ar); pulverização com assistência de ar na barra nas velocidades de 9, 11 e 29 km h-1, sobre alvos artificiais, no controle da ferrugem asiática, em diferentes partes das plantas. Para a superfície adaxial das folhas, na parte superior das plantas, a assistência de ar com 11 km h-1, proporcionou maiores depósitos na superfície das folhas. Na parte inferior das plantas não houve diferença significativa entre os tratamentos. Quanto aos depósitos na superfície abaxial das folhas, na parte superior da planta, a velocidade de ar máxima gerada pelo ventilador (29 km h-1), proporcionou maiores níveis de depósitos. A assistência de ar proporcionou maior produtividade da soja, diferindo da pulverização convencional (sem ar) e testemunha (plantas não tratadas).

Sources of Soybean Rust Resistance Challenged with Single‐Spored Isolates of Phakopsora pachyrhizi

ABSTRACTSoybean rust, caused by the fungus Phakopsora pachyrhizi Syd., is a potentially devastating disease that can cause significant yield losses. Resistance in soybean [Glycine max (L.) Merr.] germplasm, both qualitative and quantitative, may be effective in providing at least partial control of soybean rust. A number of soybean genotypes have resistance to soybean rust, but few of these have been challenged with the recently recovered U.S. isolates. The objective of this study was to evaluate known sources of soybean rust resistance against U.S. isolates of P. pachyrhizi Twenty‐eight soybean genotypes that either contained known major‐genes for resistance or had been reported as new sources of soybean rust resistance, along with two susceptible checks, were challenged with six P. pachyrhizi isolates collected in the U.S. All six isolates produced similar phenotypic reactions within each of the genotypes. Five genotypes, including the Rpp1 source and the isoline of ‘Williams 82’ with Rpp1, had no visible lesions. Eleven genotypes produced red‐brown lesions with few uredinia, including the sources of Rpp2 and Rpp3, and the remainder had susceptible tan lesions, including the source of resistance for Rpp4 Uredinial counts from genotypes producing red‐brown lesions on live and fixed leaflets showed significant variation in the number of uredinia with a genotype × isolate interaction. Uredinial counts from genotypes producing tan lesions on live and fixed leaflets showed significant variation in the number of uredinia among genotypes, but there was no genotype × isolate interaction. There were significant correlations (r = 0.8, P < 0.0001; and r = 0.4, P < 0.0001) between uredinial counts based on live and fixed leaflets within genotypes producing red‐brown lesions and those producing tan lesions, respectively.

Fungicides Associated with Two Adjuvant Formulations for Preventive and Curative Soybean Rust Control

Abstract This two-year study targeted measuring the effect of three different fungicide formulations in order to control soybean rust (Phakopsora pachyrhizi). This study also measured the effect of controlling soybean rust by adding a fixed concentration, 1 % v/v of two adjuvants into the three fungicide formulations and then varying the concentration of the two adjuvants at 0.5, 1.0, and 1.5 % into a tebuconazole formulation only. The first year of the study was conducted in the field in two regions of the Paraná State (Southern region of Brazil). The second year of the study was conducted in a greenhouse and in the field.

Eficiência do controle da ferrugem asiática da soja em função do momento de aplicação sob condições de epidemia em Londrina, PR

Asian soybean rust control efficacy as a function of application timing under epidemic conditions in Londrina, PR

Evaluation of Sequential Fungicide Spray Programs for Control of Soybean Rust

Soybean rust (SBR), caused by the fungus Phakopsora pachyrhiza, has been a recurring problem for soybean growers in the southern United States. In some cases, growers in this region have followed a fungicide spray program consisting of two fungicide applications to protect their crop from the disease. Our study was conducted to determine how various sequential fungicide spray programs perform under the relatively high SBR pressure found in Alabama. Results from this study suggest that there are significant differences in the relative effectiveness of a program based on products used and the sequence in which they are applied. Factors such as recent weather conditions, proximity to sources of SBR, cost of available products, and an estimate of a crops yield potential should be considered when choosing a fungicide program. Accepted for publication 10 February 2009. Published 2 April 2009.

Efeito de pontas de pulverização no controle químico da ferrugem da soja

O controle químico eficiente da ferrugem asiática da soja depende da correta seleção da ponta de pulverização. Este trabalho teve o objetivo de avaliar o efeito da utilização de diferentes pontas de pulverização na aplicação de fungicida para o controle da ferrugem da soja. O ensaio foi conduzido no delineamento em blocos ao acaso, com quatro repetições, em esquema fatorial (4 x 2) + 1: quatro tipos de ponta de pulverização (jato plano defletor duplo, jato plano duplo com pré-orifício e jato cônico vazio com e sem indução de ar), dois volumes de aplicação (150 e 200 L ha-1) e um tratamento adicional que não recebeu fungicida. Realizou-se a semeadura direta da cultivar de soja M-SOY 8008 (ciclo precoce), avaliando-se, após a aplicação do fungicida tebuconazole, a deposição de calda no dossel da cultura, a severidade da ferrugem, o grau de desfolha e a produtividade. Concluiu-se que não houve influência dos tipos de pontas de pulverização e dos volumes de calda no controle da ferrugem. Na parte inferior do dossel, a cobertura proporcionada com a utilização das quatro pontas foi inferior a 7% da área, sendo, portanto, necessário buscar estratégias que incrementem essa deposição. O fungicida reduziu a severidade da ferrugem da soja, o que refletiu na produtividade, que foi, em média, 157% superior à obtida na testemunha.

Utilização de glifosato para o controle de ferrugem da soja

O objetivo deste trabalho foi avaliar o efeito de glifosato sobre a germinação de esporos de Phakopsora pachyrhizi e no controle da ferrugem da soja, aplicado preventiva e erradicativamente, em condições controladas. A germinação de esporos foi avaliada tendo-se vertido, em meio de cultura, soluções de esporos com diferentes concentrações do glifosato (0, 100, 1.000, 10.000 e 20.000 ppm) e fungicidas. Para avaliar o controle da ferrugem, plantas foram pulverizadas com glifosato, com variação da dose e do momento, tendo-se medido a severidade da doença. Houve efeito do produto sobre os esporos do fungo, o que reduziu sua germinação. As pulverizações em plantas, em casa de vegetação, mostraram um efeito do produto sobre a ferrugem, quando aplicado preventivamente, porém com período de proteção curto e fungitoxicidade inferior à do fungicida tebuconazole. O uso do glifosato, avaliado nesse ensaio, não deve ser visto como medida de manejo de ferrugem, e não interfere nas práticas habituais de controle da ferrugem da soja.

Mammalian Cell Cytotoxicity Analysis of Soybean Rust Fungicides

The identification of soybean rust, caused by Phakopsora pachyrhizi H. Sydow & Sydow, in the southern United States in November 2004 (Schneider et al. 2005), in the Midwest in 2006 (Hartman et al. 2007), and elsewhere has increased the concerns of the impact of the pathogen on US soybean production (Miles et al. 2007). The rapid spread of P. pachyrhizi and its potential to cause severe yield losses makes this among the most destructive foliar diseases of soybean. Yield losses of 20%–60% were reported in Asia, with losses of 80% reported from experimental plots in Taiwan (Hartman et al. 1991). Soybean rust could have a major impact on both total soybean production and production costs in the US. The primary control of soybean rust has been with fungicides (Miles et al. 2003). There are four fungicides commercially available in the US that are registered for use on soybean and labeled for soybean rust. These fungicides are Bravo , Echo , Headline , and Quadris . Headline and Quadris are strobilurin products; Bravo and Echo are chlorothalonil products. In addition, there have recently been Section 18 Emergency Exemption requests for additional fungicidal compounds (myclobutanil, tebuconazole, propiconazole, tetraconazole, and trifloxystrobin) and mixtures of compounds (trifloxystrobin and propiconazole; propiconazole and azoxystrobin; and pyraclostrobin and tebuconazole) submitted to the EPA by the Departments of Agriculture from many states (U.S. EPA 2006a). A number of commercial products (e.g., Bumper , UpperCut , Quilt , Laredo , and Stratego ) containing these requested fungicidal compounds have been approved and may now be registered (Section 3 registration status) for management of soybean rust on soybean (U.S. EPA 2006a). While these fungicides have been used on crops (e.g., fruits, vegetables, and cereals), many questions remain regarding the large-scale application of these compounds to soybeans (~74 million acres in the US) in the prevention and treatment of soybean rust. Indeed, there is growing concern about the use of these fungicides since little is known about the toxicity of many of these compounds and their impact on human health. Therefore, the goals of this project were to assess the toxicity of soybean rust fungicides (Table 1) using a mammalian cell cytotoxicity assay and to compare the cytotoxicity (%C1/2) of these fungicides to the published toxicity values of other agrichemicals (insecticides and herbicides).