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November 5, 2018

First Case of Soybean Rust reported in Commercial Fields in Brazil

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

Agronomist in Brazil reported the first confirmed case of soybean rust in a commercial soybean field last week in the municipality of Cafelandia, which is located in western Parana. The agronomists for the Copacol cooperative indicated that this is about 15 days early for the first case to be reported.

Soybean rust is showing up early this year because the soybeans in western Parana were planted early. Approximately 50% of the soybean planted in the region went in the ground about 15 days earlier than normal. Historically, soybean planting in western Parana starts toward the end of September, but this year the planting started immediately after the end of the soybean free period on September 10th.

The weather this year has also been conducive for the early spread of rust spores that have "over wintered" in volunteer soybeans in the region. All volunteer soybeans are supposed to be eliminated during the soybean-free period, but it is virtually impossible to eliminate all the live soybean plants. Therefore, there is always a limited source of rust spores originating from these volunteer soybean plants found along the edges of the field, along roadways, and around storage and transportation facilities.

The recent wet weather has also left the leaves receptive to rust invasion and the daytime temperatures have been in the range of 20 to 25°C (68 to 77°F), which is ideal for spore dispersion.

Emater-PR, which is the state's extension service, has collaborated with 113 farmers in Parana to set up a system to detect when live soybean rust spores appear on their farm. As of last Friday, the system had detected spores on five different farms in western Parana. The goal of this detection system is to alert farmers when rust spores are in their area and the intensity of the outbreak. The system is used to orientate farmers as to when they should be applying fungicides in order to control the disease.

During the 2016/17 growing season, the average in Parana was 2.4 applications of fungicides to control soybean rust. On farms with the monitoring system, the average was 1.5 applications of fungicides and these farms did not suffer any loss of productivity due to rust even though they applied less fungicides. The key is knowing the optimum timing of fungicide applications based on the severity of the disease. Without an accurate assessment of the severity of the disease, farmers are just blindly applying fungicides without regard if it is needed or not.