Asian Soybean Rust - Risk Assessment

Sentinel Plot Program

The checkoff-supported sentinel plot program is an extensive system of monitored plots in U.S. soybean-producing states. The program is a cooperative effort of the NSCRP and USB (green) and the USDA (orange).

Soybean rust monitoring and forecasting in North America

Until rust-resistant soybean varieties are in place, a major decision that producers will face is if the potential for rust merits the application of a fungicide. A national monitoring and forecasting network is in place to help producers assess the risk of soybean rust as the season progresses.

Since soybean rust does not overwinter in the north, and must spread from south to north during a growing season, those in the North Central region can continually monitor the situation and adjust their decisions accordingly.

The network is designed to give producers a seven-day notice of when rust could arrive. It consists of

• a network of fields or plots monitored regularly for the presence of soybean rust (sentinel plots)
• a program that monitors the hosts of the rust pathogen
• a spore-tracking system that determines the presence of soybean rust spores
• climate-based epidemiological models that help to forecast spore spread and deposition

The advance warning network may be the soybean producers' best tool to manage rust. It is the most aggressive disease-monitoring program ever developed and is the collaborative effort of many universities, federal agencies, and checkoff organizations. Information from the sentinel plots is mapped and posted at the USDA Pest Information Platform for Extension and Education (PIPE). More than 475 people were involved in the sentinel plot system in 2007, and over 13,412 observations were uploaded to the PIPE website. This represents an enormous amount of cooperative work!

The risk of soybean rust movement into the North Central region will depend on three key factors:

• The occurence of soybean rust during the spring and early summer in the Gulf Coast area, which determines the amount of spores to blow northward;
• The weather conditions in July-August in the northern United States: if the weather is hot and dry, then rust will be less of a concern than if the weather is cool and wet. Rust requires wet leaf periods of at least 8 hours (in the form of rain or dew) and moderate temperatures of 60 to 80° F.
• The northward movement of soybean rust spores in weather systems.

Assessing seasonal epidemics by monitoring the northward movement of rust spores

Source: Timeline to Assess the Risk of Soybean Rust for a Growing Season X.B. Yang, ISU

Producers and their advisors can assess the risk of seasonal epidemics by monitoring the northward movement of rust spores at critical times and in critical regions of the southern United States.

In March, monitor information on outbreaks of Asian soybean rust in Florida and southern Texas. This would be an early indication that rust spores would likely move to the Gulf Coast states and north.

April, May and June are critical months. Watch for soybean rust occurring in Louisiana, Mississippi and Alabama. These are potential regions that would act as a rust pathway to the north. Texas and Georgia also are regions to watch, but with less of an impact on the northern region. If outbreaks occur on soybean plants or kudzu in April and May, the spores are likely to reach northern soybean regions as early as in July. Rust outbreak in June in the south is important but not as great as that in May or earlier.

April and May are also important time periods to check the Climate Prediction Center at NOAA. July and August are critical months for the North Central soybean region, so the prediction with 3-month lead time is a good one to look for. A prediction that includes normal to below normal temperatures and normal to higher moisture levels would be suitable for rust occurrence in the mid North Central region.

Crop Insurance

The brochure Soybean Rust, Crop Insurance and You, from the USDA Risk Management Agency, outlines how insured farmers must seek out and follow the good farming recommendations of agricultural experts such as extension agents and certified crop consultants—and also document the advice received and actions taken. It recommends that farmers follow the development and spread of Asian soybean rust, as well as treatments that may apply to their situation. View USDA publication (pdf) »

Research papers on the risk of soybean rust in the U.S.

Pan, Z., X.B. Yang, S. Pivonia, L. Xue, R. Pasken, and J. Roads, 2006. Long-term prediction of soybean rust entry into the continental United States. Plant Disease 90: 840-848.

Pivonia, S., X.-B., Yang, and Z. Pan, 2005. Assessment of epidemic potential of soybean rust in the United States. Plant Disease 89: 678-682.

Assessment of the Potential Year-Round Establishment of Soybean Rust Throughout the World
S. Pivonia and X.B. Yang
Plant Disease, May 2004 (pdf).

Looking to China to Evaluate the Risk of Soybean Rust in the U.S. (link to ISU)
X.B. Yang, Iowa State University

Knowing the risk of soybean rust by comparison with Brazil (link to ISU)
X.B. Yang, E.M. Del Ponte, and A.P. Dias
Department of Plant Pathology, Iowa State University

Information on these pages is from the cooperative effort of researchers throughout the North Central states. Information from this site can be copied and distributed for educational use. Please credit the source with our name and URL: NCSRP Plant Health Initiative at www.planthealth.info. Please do not use copyrighted photos without permission.