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December 1, 2015

Rio Grande do Sul Reports Most Cases of Soybean Rust in Brazil

One of the results of this year's strong El Nino has been a profileration of soybean rust in Brazil's southernmost state of Rio Grande do Sul. According to Embrapa, there have been 30 confirmed cases of the disease in the state, which is the most of any state in Brazil. The vast majority of the cases thus far have been on volunteer soybeans, but Embrapa is now reporting that the disease has also been confirmed in commercial fields of soybeans as well.

Nationwide, there are now 75 confirmed cases of soybean rust in Brazil. Last year at this time there were 44 cases nationwide and 17 in Rio Grande do Sul. Rust has now been confirmed in commercial soybean fields in all for southern states of Brazil - Sao Paulo, Parana, Santa Catarina, and Rio Grande do Sul.

The reason for the increased number of rust cases has been the wet weather in southern Brazil associated with the strong El Nino. This has allowed the soybeans spilled during harvesting and transport to germinate and act as host plants for the disease. Additionally, El Nino resulted in mild winter temperatures in southern Brazil. Normally, the state of Rio Grande do Sul experiences freezing temperatures during their brief winter season which kills the volunteer soybeans, but those temperatures did not occur this year allowing all the volunteer soybeans to survive.

Wet weather has also delayed the soybean planting and stretched out the soybean planting in the state. The extended planting period could also result in more cases of rust especially for the later planted soybeans.

Brazilian scientists are advising farmers in the state to rotate the fungicides they use to control the disease because some of the chemicals have lost much of their effectiveness due to the disease developing resistance. Embrapa is encouraging farmers in the state to visit their web site to see the results of tests they conducted last growing season comparing the effectiveness of the various fungicides.