Asian Soybean RustIdentification & Treatment Guide 2026
Phakopsora pachyrhizi · Family: Phakopsoraceae
Asian soybean rust (Phakopsora pachyrhizi) causes tan to dark brown pustules on leaf undersides, leading to rapid defoliation and 10-80% yield loss. No durable resistance exists. Manage with preventive fungicide applications (triazole + strobilurin) at R1-R2 stage, early planting, monitoring sentinel plots, and observing the vazio sanitário (soybean-free period) in Brazil.
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criticalAsian Soybean Rust
- Affects
- leavespetiolesstemspods
- Peak Season
- Humid weather with temperatures 18-26°C and prolonged leaf wetness; mid to late growing season
- Spread Risk
- Fast
- Spread By
- Windborne urediniospores (can travel thousands of km), rain splash
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Symptoms: What does Asian Soybean Rust look like?
Visual identification guide — tap each stage for details
Tiny tan angular lesions on lower leaves
Small (1-2 mm) grayish-green to tan angular spots appear on lower leaves, often overlooked without close inspection using a hand lens.
Tan to brown pustules on leaf underside
Lesions develop raised pustules (uredinia) on the lower leaf surface. Pustules are tan to dark brown and produce abundant powdery spores. Multiple pustules per lesion are characteristic.
Rapid defoliation and pod fill failure
Leaves yellow and drop rapidly. Severe defoliation during pod fill causes shriveled seeds, reduced pod count, and dramatic yield loss. Complete defoliation can occur within 2-3 weeks of symptom onset.
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