Soybean Diseases Have Impacted Iowa Harvest Quality
Farmers and seed retailers should monitor for fungal decay and adjust drying procedures to protect germination rates.
Updated on Oct. 6, 2026 in Agriculture
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Recent wet and warm weather across Iowa has fueled the development of purple seed stain and Diaporthe seed decay in the 2026 soybean crop. These conditions threaten seed quality and germination potential as producers navigate a delayed harvest.
Why it matters
Fungal infections can significantly degrade crop quality and lower yield potential for the 2027 planting season. Managing moisture levels and identifying infection rates early are essential for maintaining the viability of stored seed stock.
Seed treatments can lift germination rates by 10% to 15% for impacted crops. Operators must track the 19% moisture threshold, as fungal growth persists while moisture remains above this level.
The players
Iowa State University Seed Lab
An academic institution that provides agricultural testing services and diagnostic support for state producers.
The details
The Diaporthe fungus primarily infects pods, subsequently spreading to the seeds and resulting in cracked, shriveled beans with chalk-colored mold. Purple seed stain causes characteristic discoloration, further complicating quality assessment. Effective management requires drying seeds to below 19% moisture, which halts further fungal development, while dry storage over winter can help stabilize quality for some affected lots.
Timeline
Late September 2026: Purple seed stain was observed in a central Iowa field.
February 2027: Growers should conduct retesting of seeds that have been dry-stored through the winter.
Spring 2027: Producers may face lower germination rates and seedling blight if infected seeds are used.
Market Landscape
This fungal outbreak follows an unusually wet and warm weather pattern that disrupted the 2026 Iowa soybean harvest. The situation mirrors historical challenges where moisture-driven decay forces growers to re-evaluate seed viability before the upcoming planting season.
Operators should prioritize moisture testing for all harvested soybeans to prevent further fungal spread in storage. Seed lots with more than 20% Diaporthe infection should be flagged, as these are expected to fail germination requirements.
The takeaway
Producers should act now to dry stored seeds below 19% moisture to kill the Diaporthe fungus mycelium. Monitor for symptoms of seedling blight this spring and consult with local laboratory services for germination testing before purchasing or planting 2027 seed stock.
What happens next
The Iowa State University Seed Lab will offer germination testing for seeds intended for the 2027 growing season.
Further reading
For more on managing crop health and seasonal planting challenges, visit our Agriculture section.
Source note: This article includes information reported by Farm Progress.
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