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December 7, 2016

Six Confirmed Cases of Rust in Commercial Soybean Fields in Brazil

Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.

Embrapa is now reporting that there have been 27 cases of soybean rust confirmed in Brazil with 6 cases in commercial soybean fields and 21 cases in volunteer soybeans. The latest case in commercial soybeans was in the state of Mato Grosso do Sul. There have also been three confirmed cases of soybean rust in commercial soybean fields in Parana and two in Sao Paulo. The total of 27 cases in Brazil compares to 92 cases last year at this time (both in commercial fields and in volunteer soybeans) and 36 cases for the 5-year average.

Thus far this growing season, soybean rust has basically been a non-issue in Brazil. It remains to be seen if that changes going forward, but one advantage this year is that many of the soybeans were planted earlier than normal, which means that they will be exposed to the disease for a shorter period of time. In the state of Mato Grosso for example, the soybeans were planted 2-3 weeks earlier than last year and in some locations the soybeans were planted at a record fast pace.

Soybean rust entered Brazil during the 2000/01 growing season and it is estimated to have cost Brazilian farmers at least US$ 10 billion in control cost and lost productivity. In recent years, the disease has developed resistance to some of the commonly used fungicides in Brazil. As a result, scientists are urging farmers to rotate the chemicals that they use and to use chemicals with different modes of action in order to slow the development of even more resistance. If left untreated, yield losses can be as high as 80%.

The worst year for soybean rust in Brazil was during the 2008/09 growing season when there were 3,514 confirmed cases. The best year was the 2011/12 growing season when there were 261 confirmed cases.

It was the concern about soybean rust that led the state legislature in Mato Grosso to adopt new guidelines as to when soybeans may be planted and harvested in the state. Starting with the 2016/17 growing season, the soybeans in Mato Grosso may be planted starting on September 15th and the planting must be completed by December 31st. All the soybeans must then be harvested by May 5th when the new soybean-free period begins. Then from May 5th to September 15th, there are no live soybean plants permitted in the state. The soybean-free period was put in place to slow the spread of the disease from one growing season to the next.

The new legislation also prohibits the planting of two crops of soybeans in the same field during one growing season, commonly known as safrinha soybeans. In recent years, there have been approximately 250,000 hectares of safrinha soybeans planted in Mato Grosso. Scientists found that the second crop of soybeans greatly increased the chances of the disease spores remaining viable until the next crop of soybeans were planted. Currently, only Mato Grosso has prohibited safrinha soybean production, but other states are expected to adopt the same prohibition over the next few years.