Epidemics of soybean rust (Phakopsora pachyrhizi) in Brazil and Paraguay from 2001 to 2003

In 5 March 2001, a severe rust outbreak was recorded at Pitapó, Paraguay, and the causal organism was determined to be Phakopsora pachyrhizi using polymerase chain reaction (PCR) and DNA sequence analysis. In May, rust surveys showed spread throughout most of Paraguay and into western and northern Parana, Brazil. In the 2001-02 season, rust was widespread in Paraguay, but losses were reduced due to severe drought; however, in Brazil it spread to more than 60% of the soybean acreage, causing field losses estimated at 0.1 million metric tons (MMT). In 2003, the disease was observed in more than 90% of the fields in Brazil, and the projected losses in Mato Grosso and Bahia alone are 2.2 MMT (US$487.3 million). Approximately 80% of the soybean acreage in Brazil was sprayed twice with fungicides at the cost of US$544 million. Differences in efficacy have been observed among the commercial strobilurin and triazol fungicides.