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November 19, 2015

Soybean Rust Moving into Commercial Soybean Fields in Brazil

Soybean farmers in southern Brazil have been alerted by scientists that soybean rust has now been detected in commercial soybean fields in Sao Paulo and Parana. The arrival of the disease in commercial fields is coming about a month earlier than last year. Embrapa is now reporting 66 confirmed cases of soybean rust with 11 of those cases in commercial soybean fields.

The state of Rio Grande do Sul has the most confirmed cases with 29, followed by Parana with 17, Sao Paulo with 10, Mato Grosso with 5, Mato Grosso do Sul with 2, and Minas Gerais, Santa Catarina and Tocantins with one each. Last year at this time there were 40 confirmed cases and the ten-year average is 10 confirmed cases.

Up until this point, nearly all the confirmed cases of soybeans rust have been identified in volunteer soybeans. These are soybeans that were spilled during harvesting or in transport and subsequently germinated in the field or alongside highways and around storage facilities. These volunteer soybeans can harbor the disease in between growing season and is the main reason why most Brazilian states have adopted a soybean-free period during which land owners are directed to destroy all live soybean plants.

The main reason why there have been so many cases of rust in volunteer soybeans this year is the persistent wet weather in southern Brazil associated with El Nino. Additionally, El Nino has also resulted in mild weather during the winter season in southern Brazil. Normally, occasional frosts in southern Brazil would kill the volunteer soybeans, but that did not happen this year, which allowed the soybeans to profligate.

Finding rust in soybean fields this early in the growing season does not necessarily mean that the soybean yields will be impacted, but it does mean that farmers will be spending more money on additional fungicide applications in order to control the disease. The later planted soybeans could have a more significant problem because those fields will be exposed to the disease for a much longer period of time. Farmers are concerned because chemical costs have risen this year due to a depreciation of the Brazilian currency. Therefore, more applications mean higher costs at a time when profit margins are already thin.

Scientists are warning farmers not to try and save money by limiting fungicide applications or by using cheaper chemicals that may not be as effective against the disease. They are advising farmers to use the most effective chemicals and to rotate their chemical use in order to put less pressure on the disease to develop resistance to the fungicides.

Embrapa has been tracking soybean rust in Brazil since the 2005/06 growing season. The worst year was 2008/09 when 3,514 cases of the disease were confirmed. The best year was 2011/12 when just 261 cases were confirmed. Brazilian scientists and farmers have been doing a much better job in controlling the disease. As an example, the 10-year average for the number of cases per year is 1,389, but if you look at just the last five years, the average is 428 cases.