Nov 12, 2015

Soybean Rust Confirmed in Parana a Month Earlier than Last Year

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

Brazilian scientists have confirmed two cases of soybean rust in commercial soybean fields in the state of Parana. The two cases were found on the sixth and seventh of November in the cities of Tibagi and Ponta Grossa. This is a month earlier than last year when the first case was confirmed in Parana on December 3rd. Last week, Embrapa identified the first case of soybean rust in commercial soybeans in the city of Itabera in the state of Sao Paulo.

All three of these infected soybean fields were planted immediately after the soybean-free period ended on September 15th and the soybeans are now flowering. Scientists are recommending to farmers to immediately start applying fungicides to their soybeans as soon as the disease is identified in their area.

Embrapa has already identified 30 cases of soybean rust on volunteer soybeans in the states of Rio Grande do Sul and Santa Catarina with another 15 cases on volunteer soybeans in the state of Parana. The greater than normal number of cases of rust on volunteer soybeans can be explained by El Nino.

There is no soybean-free period in Brazil's two southern-most states of Rio Grande do Sul and Santa Catarina because freezing temperatures during the brief winter period usually kills any volunteer soybeans. That did not happen this year due to El Nino causing heavy rainfall and mild temperatures across southern Brazil. In fact, the heavy rains in southern Brazil over the winter period resulted in more than the normal number of volunteer soybeans that acted as host plants for the disease.

Due to the earlier than normal confirmation of soybean rust, scientists are already warning farmers in southern Brazil that any late planted soybeans will require a greater than normal number of fungicide applications and shorter intervals between applications.

This growing season will be the last time that farmers in Parana will be allowed to plant safrinha soybeans. Starting with the 2016/17 growing season, the planting of back-to-back crops of soybeans during the same growing season will be prohibited.

Any farmer in Parana that plants safrinha soybeans in January or February of next year can anticipate very heavy disease pressure from soybean rust. Last year for example, some fields of safrinha soybeans in Parana received up to six fungicide applications. As one scientists stated, last year it seemed like soybeans germinated already infected with the disease. Additionally, the number of effective fungicides is declining as the disease develops resistance to some of the fungicides. As a result, scientists are advising farmers to rotate the types of fungicides they use in order to slow down the development of even more resistance.

Last safrinha soybean crop in Parana. Last year safrinha soybeans were sprayed six times due to the amount of rust spores available, the soybeans germinated with the disease.