EN 
PT_BR Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, registered its first occurrences in October 2024 in Rio Grande do Sul, shortly after the end of the sanitary break, in crops in Cruz Alta. Monitoring carried out by the Department of Agricultural Diagnosis and Research of the Secretariat of Agriculture, Livestock, Sustainable Production and Irrigation (DDPA/Seapi) and by Emater/RS-Ascar detected high levels of spores (infection) in the initial weeks of the 2024/25 crop season, with emphasis on Muitos Capões (602 spores), Três Passos (372), Ijuí (293) and Cruz Alta (205).
The results are included in Technical Circular No. 29 – Monitoring Program for Rust in Rio Grande do Sul. October and November concentrated the highest levels of inoculum, followed by March. Among the regions, the Central Plateau presented the most critical situation, with 5,584 spores, followed by the Upper Plateau–Northeast Mountains (2,908) and the Upper/Middle Uruguay Valley (2,281). The analysis indicated that the fungal peaks occurred shortly after periods of rain and under conditions of high relative humidity.
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Despite the high initial infection rate, the climate slowed the spread of the disease. The 2024/25 crop season was marked by climate neutrality—without a predominance of El Niño or La Niña—but with below-average rainfall in much of the state and heat waves in February and March, when temperatures exceeded 41°C. These factors reduced the formation of new outbreaks and resulted in less spread than observed in the previous crop season, when El Niño favored greater dissemination of rust.
The study also involves the participation of other research institutions, in addition to the Department of Plant Protection (DDV/Seapi). The director of the DDV highlights that the objective is to monitor the presence of the fungus in soybean production areas and identify the meteorological conditions favorable to its development, allowing for the creation of a risk prognosis for the occurrence of Asian soybean rust. “The information generated can be used to initiate disease control and to make decisions regarding the use of fungicides,” emphasizes Ricardo Felicetti.
Research and monitoring
The aerobiological monitoring program for soybean rust in Rio Grande do Sul maintains spore collectors in 77 soybean fields, distributed across 75 municipalities representing the state's 11 ecoclimatic regions. The data is updated weekly and made available on online maps, assisting producers in the preventive management of the disease.
According to Dr. Andréia Mara Rotta de Oliveira, a phytopathologist at Seapi and one of the study's authors, the results of the Technical Circular "reinforce the relevance of climate monitoring combined with pathogen surveillance as an essential strategy for the preventive management of Asian soybean rust."
Currently, the state is observing the soybean sanitary break period, in effect from July 3rd to September 30th, during which the maintenance of volunteer plants or plants in any stage of development is prohibited. This measure is considered fundamental to reducing the survival of the fungus between harvests.
