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

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

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

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

Sentinel plots for controlling soybean rust

Timely application of fungicides is the only way to effectively and efficiently protect soybean crops from soybean rust infections. Because we do not know when and where the disease outbreaks will occur in the coming season, early detection of soybean rust during the growing season is key for timely applications. Over the past few years in other countries, sentinel plots have been effective in detecting the disease early and guiding producers in making better spray decisions

Soybean rust outlook - June 13

This year\u27s hurricane season started early and the arrival of Tropical Storm Arlene has raised some concerns regarding the risk of soybean rust (SBR) this season. The early start of the hurricane season reflects some similarities between the soybean rust situation and the southern corn leaf blight epidemic in 1970. In that epidemic, one major condition was an unusual tropical storm that occurred in June, which facilitated the spread of the southern corn leaf blight (SCL) pathogen from southern Mississippi and Alabama to the northern Corn Belt