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Corn+Soybean Digest

Forecasting Soybean Rust

Since Asian soybean rust was first identified in Louisiana last November, and eight Southern states since then, the American soybean industry has been on alert for the disease. Researchers anticipate a high likelihood that soybean rust will reappear during the 2005 growing season, but it is uncertain when and where the first confirmed cases may appear and how the disease may spread after that.

Surveillance and scouting of host plants and sentinel soybean plots are underway to detect severity and spread of the disease. To further assist growers in preparing for this new disease challenge, researchers have diligently been working to develop forecast maps that may help predict future aerial dispersal of soybean rust spores, deposition of spores onto soybean plants and the development of the disease across the U.S.

The forecasts, which are displayed as easy-to-read color maps, are being posted daily on the Internet at

In addition to model predictions, scouting observations will be overlaid on the maps. These observations will be used to verify the presence of the disease and help calibrate the forecast models. It's anticipated the forecast models will be updated three times weekly from now through October.


Development of the forecast maps is a collaborative effort among researchers and field personnel within USDA's Animal Plant and Health Inspection Service (APHIS), the Agricultural Research Service (ARS), the Cooperative State Research, Education, and Extension Service (CSREES) and university-based Cooperative Extension Services. Many of these collaborators will also participate in the scouting of soybean rust, along with state department of agriculture employees and industry field representatives.

The actual model development is being led by Scott Isard, an aerobiologist at Penn State University in collaboration with Charlie Main of North Carolina State University (NCSU) and Joe Russo of ZedX, Inc., an information technology company specializing in the development of weather-dependent, decision-support products.

The model is unique in its ability to combine regional spore transport and local disease development data by taking into consideration weather factors such as rain, which can wash the spores out of the air; ultraviolet radiation, which kills the airborne spores while they travel; and wind to predict spore movement and survival.

The soybean rust model builds on the successes of earlier forecast trajectory models, developed to predict tobacco blue mold and cucurbit downy mildew. Because the new model represents an advanced design, those involved believe the forecasts it generates will provide the most detailed tracking of disease behavior to date.

By using the model in 2004, the team led by Isard predicted early last summer the likelihood that soybean rust spores could be carried from sources in South America to the Gulf Coast of the U.S. via a vigorous hurricane season. After Hurricane Ivan passed and rust was found in Louisiana, the transport models were used again to guide scouts to likely areas in the southeastern U.S. to look for other infections. Using this guidance, rust was found in a total of nine states.

AS THE 2005 soybean growing season progresses in the U.S., the soybean rust model has been enhanced to include not only spore transport and survivability, but also timing with susceptible stages of a soybean crop and local disease development.

Output from the improved model will be used to predict the movement of spores and develop maps to guide scouting and surveillance efforts of host plants and sentinel plots. As survey teams confirm the locations of soybean rust occurrences in the U.S., the updated information will further refine the model predictions.

By accessing the link provided on the USDA Web site, growers can view county-level scouting instructions, official confirmation of disease presence, and timely guidelines for disease control provided by state specialists.

Cooperative Extension specialists and researchers alike in U.S. soybean growing areas are looking forward to this season's Web-based products resulting from the collaborative modeling effort. “This should really be a good tool to help soybean growers manage risk,” says Penn State Plant Pathologist Erick DeWolfe. He further suggests that “producers should use these forecasts as a cue to step up monitoring efforts if they are in a higher risk zone, and if appropriate make fungicide spraying preparations.”

Steve Koenning, a NCSU plant pathologist, echoes DeWolfe's sentiment saying that the modeling system should be a valuable tool for soybean growers to better plan rust management strategies.

“By combining the forecast map information with the maps that indicate where soybean rust has been confirmed, growers should be able to make a more informed decision on whether to spray and when,” Koenning says.

As with any new decision support tool, DeWolfe cautions that “this will be a learning year.” However, he adds, “We have a lot of people with experience in managing this disease, and these forecast models are just one more source of information to make their recommendations more precise.”

More On Rust

Rust Tracks, which provides up-to-date information about Asian soybean rust, is sponsored by Syngenta Crop Protection. For more information about soybean rust, visit Syngenta's Web site,

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