Brazil Maintains Dominance in Global Soybean Production
19 December 2024, Brazil: For the past four years, Brazil has held the title of the world’s leading soybean producer, with over 70% of its output allocated for export. As of November 2024, the nation reported foreign sales totaling US$42.08 billion, with the 2024-2025 harvest already covering 90% of the anticipated area, as per data from the National Supply Company (Conab). However, the ongoing threat of Asian rust poses a significant risk to crop yields.
Asian rust, caused by the fungus Phakopsora pachyrhizi, is prevalent across all soybean-producing regions in Brazil and can drastically reduce yields by as much as 90%. The disease begins when spores produced on host plants during the off-season are dispersed by the wind and land on soybean leaves. Optimal conditions for germination occur when temperatures range from 18°C to 26°C and the leaves remain wet for at least six hours. Once germinated, the fungus infiltrates the leaf tissues, leading to infection.
Symptoms of Asian rust include small spots on the leaves that develop into gray or brown lesions, primarily on the underside. Additionally, small blister-like structures, known as uredia, may appear, leading to early leaf drop and hindering grain development. Each uredium can produce spores for approximately 21 days, facilitating the spread of the disease both within the crop and to distant areas. The fungus can survive on soybean plants and in certain habitats even after the growing season ends.
Strategies to Combat Asian Rust
Due to the high genetic variability of the fungus, breeding resistant soybean varieties poses a challenge. Consequently, chemical control remains the most effective strategy. “To achieve the best results, producers must select suitable fungicides and apply them at the right time, adhering to the manufacturer’s guidelines to prevent the development of resistance,” stated Fábio Kagi, Regulatory Affairs Manager at the National Union of Plant Protection Products Industry (Sindiveg).
Ongoing monitoring of crops is crucial. Regular inspections allow for the early detection of disease symptoms, enabling prompt intervention. Rotating soybeans with other crops can help reduce soil-borne fungus levels. Moreover, removing volunteer plants and other hosts is essential to prevent the pathogen from establishing itself.
Integrated crop management practices include implementing a sanitary gap—keeping fields free of soybeans for at least 60 days during the off-season, suitably adjusting sowing areas for effective spraying, and ensuring balanced fertilization. Additionally, early planting aligned with regional conditions supports soybean development in less disease-prone environments. Proper spacing between plants also enhances fungicide penetration into leaves, improving treatment effectiveness.
Addressing Root Rot Issues
Another significant challenge for soybean producers is root rot, which can lead to substantial yield losses. This disease can be triggered by various pathogens, including Phytophthora sojae, resulting in symptoms like seed rot, seedling death, and wilting of primary and secondary roots. It typically occurs in cold, acidic, and waterlogged soils. Preventative measures include using resistant varieties, improving soil drainage, practicing crop rotation, and applying targeted fungicides.
Root rot can also stem from Fusarium spp., which causes plant wilting and root discoloration, particularly in compacted, overly moist soils. Solutions focus on enhancing drainage, managing nitrogen inputs, and implementing crop rotation strategies.
“Consistent monitoring and swift action upon noticing initial disease symptoms are critical. Employing the right management practices, along with efficient pesticide use, ensures the health of soybean crops and their profitability,” Kagi concluded.
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