Jan 21, 2010
Brazil At Risk Of An Epidemic Of Soybean Rust
Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.
Worries about soybean rust in Brazil are being heightened by the persistent rainy weather that is ideal for the spread of the disease. The number of confirmed rust cases in Brazil now stands at 977, which is more than any time during the last five years. Last year at this time there were approximately 260 confirmed cases of rust. The state hit the hardest appears to be Goias with 367 confirmed cases followed by Mato Grosso do Sul with 224 and Parana with 193. Additionally, scientists and farmers are reporting that the disease appears to be more aggressive this year than in previous years.
The first confirmed case of soybean rust in Parana was reported when the early-planted soybeans began to flower, which is a month earlier than in previous years. Researchers accredit the early arrival of the disease to rainy weather during the winter, which led to the survival of more than normal amount of volunteer soybeans. Rust spores need to overwinter on a host plant and without it, they cannot survive for more than 60 days. Unfortunately, the numerous volunteer soybeans allowed the spores to persist until a new crop of soybeans had been planted. During the last several years, volunteer soybeans had not been an issue due to the dryer winter weather.
The frequent rains that have fallen this growing season have been ideal for the spread of the disease and have also made it much more difficult to adequately control the disease. Timing of the fungicide applications is critical for adequate control, but the frequent rains have disrupted the timing. Additionally, if the rainfall occurs to soon after application, some of the chemical will be washed off and the treatment will not be as effective. All throughout Brazil, farmers have also been reducing the time interval between applications in an effort to control the disease. Some farmers have reduced the interval between fungicide applications to as short as 12 days in order to keep the disease under control.
One reason why the disease may appear to be more aggressive this year is because it is developing some resistance to the traditional fungicides. As a result, Bayer CropScience is now recommending a mixture of chemicals to give a broader control. Plant breeders have identified genes that offer a level of tolerance to the disease, but the amount of seed available for the 2009-10 growing season was limited.
The amount of damage caused by the disease is yet to be determined, but in some of the hardest hit areas of western Parana, scientists are already reporting yield losses of up to 30%. Farmers in the hardest hit areas are concerned that their chemical costs are going to skyrocket and that the disease could reduce their top end yields.