Phomopsis seed decay of soybean
Phomopsis seed decay is caused by the fungus Diaporthe longicola, and can greatly affect seed quality. Phomopsis-infected seed are cracked and shriveled and are often covered with chalky, white mold. If infected seeds are planted, emergence may be low due to seed rot or seedling blight. Infected seedlings have reddish-brown, pinpoint lesions on the cotyledons or reddish-brown streaks on the stem near the soil line.
Choose varieties with the best resistance package. Tillage and rotation to non-host crops such as corn can reduce inoculum. Timely harvest will help reduce the risk of seed decay and preserve seed quality. Do not plant seed with a high incidence of Phomopsis seed decay. Currently available fungicide seed treatments generally appear to be effective against Phomopsis seed infection. Foliar fungicide applications between R3 and R5 may reduce seed infection especially in seed production fields. Fungicide may improve seed quality, but yield may not be affected.
Gallery Images: A. Tenuta and D. Mueller