Stage of detection and number of sprays for controlling soybean rust

During winter extension meetings, three of the most common questions asked about Asian soybean rust were: when will soybean rust show up in the northern United States; how early should a spray application be made; and how many sprays would be needed. It is incorrect that once soybean rust outbreaks occur in coastal regions of the Gulf of Mexico, the disease can be airborne to Iowa within 2 to 3 days and defoliate soybeans in a week or two if no chemical is applied immediately after the spores arrive. Another recent question is whether spraying at the vegetative growth stage is needed. To address all these questions, we need to know the most likely stage of soybean rust when it appears in the United States

Meteorological factors and Asian soybean rust epidemics: a systems approach and implications for risk assessment

Favorable meteorological and environmental conditions are critical components that affect Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, the most damaging fungal disease of soybean. In this review, we used available knowledge on the effect of meteorological factors affecting the disease to construct a systems-based approach to understand the risk of ASR epidemics. The systems approach is based on a hierarchical framework where relevant environmental factors that affect the key stages of the ASR disease cycle are identified and this included both aerobiological and epidemiological components. The formal framework we used examined the following epidemic characteristics: spore release, spore dispersal, spore deposition, infection efficiency, latent period and spore production. It provided the ability to identify the most important meteorological-related factors along with relevant knowledge gaps from which the implications for disease forecasting were described. This is new information that can be used as a guide for further epidemiological research and especially to develop and improve upon both local and regional risk models.Condições meteorológicas e ambientais são componentes críticos nas epidemias de ferrugem asiática da soja (FAS), doença causada pelo fungo Phakopsora pachyrhizi e que causa o maior dano na cultura da soja. Nesta revisão, o conhecimento sobre o efeito de fatores meteorológicos que influenciam nas epidemias foi usado para construir uma abordagem sistêmica para compreender o risco de epidemias de FAS. Esta é baseada em uma estrutura hierárquica onde os fatores relevantes que afetam os estágios chave no ciclo da doença foram delineados, incluindo os componentes aerobiológicos e epidemiológicos. As seguintes características epidemiológicas foram avaliadas: liberação de esporos, dispersão de esporos, deposição de esporos, eficiência de infecção, período latente e produção de esporos. O conhecimento sobre os fatores meteorológicos que afetam cada um dos componentes foi revisado, sendo identificados os fatores mais importantes e as falhas de conhecimento, bem como as implicações para a previsão da doença. A informação é importante para orientar a pesquisa epidemiológica futura e especialmente desenvolver e melhorar modelos de risco da doença em níveis locais a regionais

Soybean rust update - May 2, 2005

Based on our experience with corn rusts, we suspected that disease outbreaks occurring in Florida and southern Texas in March and April would be an indication that rust spores would likely be available to move to Gulf Coast states. The earlier an outbreak occurs in the South, the higher the risk for northern soybean production regions. Since the first detection in kudzu in central Florida in late February, no outbreak was observed in the last two months. The first detection outside Florida on volunteer soybeans was confirmed in southern Georgia

Survey of mycotoxins in Southern Brazilian wheat and evaluation of immunoassay methods

One hundred commercial wheat grain samples were collected during the 2015 sea-son across 78 municipalities in the states of Paraná (PR), Rio Grande do Sul (RS), and São Paulo (SP), Brazil. Separate subsamples were analyzed for the concentration of deoxynivalenol (DON), zearalenona (ZEA) and ochratoxin A (OTA) mycotoxins using two methods: UHPLC-MS/MS (reference method) and a commercial enzyme-linked immunosorbent assay (ELISA) (AgraQuant®). The OTA mycotoxin was not found in the samples by both methods. DON and ZEA were detected in 55 % and 39 % of the samples by the reference method, with overall mean levels of 795.2 μg kg−1 and 79.78 μg kg−1, respectively. There was a significant and positive correlation (Spearman rank) between DON and ZEA estimates by the reference method (r = 0.77, p < 0.001). The DON levels estimated by the immunoassay agreed poorly with the reference, being largely overestimated. Based on a cut-off level of 1000 μg kg−1, the immunoassay correctly classified 57 samples as true negatives and 15 as true positives. Only 28 were classified as false positives. For ZEA, the levels estimated by the two methods were in better agreement than for DON. Using the cut-off level of 200 μg kg−1, 96 % of the samples were classified correctly as true positives and only one sample was classified as false positive. The levels for both mycotoxins were mostly acceptable for human consumption. Further studies should focus on multi-toxin methods compared with immunoassays to understand the reasons of overestimation and the role of immunoassays as a cost-effective solution for fast screening of mycotoxins in the food chain

Can rainfall be a useful predictor of epidemic risk across temporal and spatial scales?

Plant disease epidemics are largely driven by within-season weather variables when inoculum is not limiting. Commonly, predictors in risk assessment models are based on the interaction of temperature and wetness-related variables, relationships which are determined experimentally. There is an increasing interest in providing within-season or inter-seasonal risk information at the region or continent scale, which commonly use models developed for a smaller scale. Hence, the scale matching dilemma that challenges epidemiologists and meteorologists: upscale models or downscale weather data? Successful applications may be found in both cases, which should be supported by validation datasets whenever possible, to prove the usefulness of the approach. For some diseases, rainfall is key for inoculum dispersal and, in warmer regions (e.g., tropics) where temperature is less limiting for epidemics, rainfall extends wetness periods. The drawbacks of using rainfall at small scales relate to its discrete nature and high spatial variability. However, for pre- or early-season predictions at large spatial scales sources of reasonably accurate rainfall summaries are available and may prove useful. The availability of disease datasets at various scales allows the development and evaluation of new models to be applied at the correct scale. We will showcase examples and discuss the usefulness of rainfall as key variable to predict soybean rust and wheat scab from field to region

Climate change impacts on the ecology of 'Fusarium graminearum' species complex and susceptibility of wheat to 'Fusarium' head blight: a review

'Fusarium' head blight (FHB) of wheat, caused mainly by a few members of the 'Fusarium graminearum' species complex (FGSC), is a major threat to agricultural grain production, food safety, and animal health. The severity of disease epidemics and accumulation of associated trichothecene mycotoxins in wheat kernels is strongly driven by meteorological factors. The potential impacts of change in climate are reviewed from the perspective of the FGSC life cycle and host resistance mechanisms influenced by abiotic pressures at the ecological, physiological and molecular level. Alterations in climate patterns and cropping systems may affect the distribution, composition and load of FGSC inoculum, but quantitative information is lacking regarding the differential responses among FGSC members. In general, the coincidence of wet and warm environment during flowering enhances the risk of FHB epidemics, but the magnitude and direction of the change in FHB and mycotoxin risk will be a consequence of a multitude of effects on key processes affecting inoculum dynamics and host susceptibility. Rates of residue decomposition, inoculum production and dispersal may be significantly altered by changes in crop rotations, atmospheric carbon dioxide concentration ([CO₂]), temperature and precipitation patterns, but the impact may be much greater for regions where inoculum is more limited, such as temperate climates. In regions of non-limiting inoculum, climate change effects will likely be greater on the pathogenic rather than on the saprophytic phase. Although the mechanisms by which abiotic stress influences wheat defences against 'Fusarium' species are unknown, available data would suggest that wheat may be more susceptible to 'Fusarium' infection under future climate conditions. Additional research in this area should be a priority so that breeding efforts and climate resilient management strategies can be developed

Models and applications for risk assessment and prediction of Asian soybean rust epidemics

Asian rust of soybean [Glycine max (L.) Merril] is one of the most important fungal diseases of this crop worldwide. The recent introduction of Phakopsora pachyrhiziSyd. & P. Syd in the Americas represents a major threat to soybean production in the main growing regions, and significant losses have already been reported. P. pachyrhizi is extremely aggressive under favorable weather conditions, causing rapid plant defoliation. Epidemiological studies, under both controlled and natural environmental conditions, have been done for several decades with the aim of elucidating factors that affect the disease cycle as a basis for disease modeling. The recent spread of Asian soybean rust to major production regions in the world has promoted new development, testing and application of mathematical models to assess the risk and predict the disease. These efforts have included the integration of new data, epidemiological knowledge, statistical methods, and advances in computer simulation to develop models and systems with different spatial and temporal scales, objectives and audience. In this review, we present a comprehensive discussion on the models and systems that have been tested to predict and assess the risk of Asian soybean rust. Limitations, uncertainties and challenges for modelers are also discussed

Timing of Triazole-Based Spray Schedules for Managing Mungbean Powdery Mildew in Australia: a Meta-Analysis

Powdery mildew (PM), caused by two fungal species, Podosphaera xanthii and Erysiphe vignae, is a yield limiting foliar disease commonly found in mungbean (Vigna radiata) cropping areas of eastern region of Australia. Effective control of the disease relies largely on fungicide applications, mainly of the triazole group. Uncertainty in the current fungicide spray schedule recommendations, which advise commencing with a spray at the first signs of PM, prompted this study to evaluate PM severity and crop yield data obtained from fungicide trials which also tested spray schedules starting before (early) or after (late) first signs, applied singly or combined with a follow-up spray. A meta-analytic approach was employed to obtain mean differences of the PM severity and crop yield between plots sprayed with specific triazole-based spray schedules and nontreated plots. From 26 trials, 14 and 15 met the criteria for inclusion in the respective PM severity and yield analyses. The schedule with the first spray starting at first sign, with a follow-up spray 14 days later, resulted in significantly lower disease severity compared to all other schedules. However, the yield protected was only numerically higher and not statistically different compared to: single-spray at first sign, single-spray late or two-spray starting late. PM severity and yield in the early sprayed plots did not differ from the nontreated plots. These findings support the current recommendations and provide additional evidence that yields are still protected when delaying the first spray up to a week after disease onset. They also suggest that additional sprays may not always be necessary, thus reducing direct fungicide costs, indirect costs due to fungicide insensitivity and potential adverse effects to the environment

Soybean rust outlook--July 18, 2005

During the past week, soybean rust was found for the first time infecting a commercial soybean field in southern Alabama, 1 mile northwest of a sentinel plot that was found to be infected three weeks earlier. Earlier this week, it was confirmed in a sentinel plot in George County, southeastern Mississippi, at very low levels. In the Alabama field, the disease level was also at very low levels, and the farmer has sprayed the field during the past weekend. The disease was also found in a second sentinel plot in Georgia