April 4, 2008 

Every year soybean producers in some part of the state struggle with damage from seedling disease. Early planting is one factor which can greatly increase the risk of seedling diseases. Cool soil, especially with extra moisture, can create stressful germination and emergence conditions that increase disease potential. The amount of damage from seedling soybean disease varies from year to year, but most producers with a history of stand problems know they are at risk. Unfortunately, with seed treatment there really is no second chance; you need to determine your risk level up front.

Conditions Warranting Seed Treatment

I recommend a seed treatment fungicide if you have any of the following conditions:

•  History of seedling/emergence problems. If you have a field with a history of stand problems, this year you will want to treat the seed with a good combination product.

•  Early planting. If you're considering early planting, fungicide seed treatments are a necessity. With a fungicide treatment, cool, wet soils are very conducive to poor stands. No-till fields will have cool soils later in the season than fields receiving some tillage. No-till field commonly will have more seedling disease problems.

•  Phytophthora history. Fields with a history of Phytophthora will need additional metalaxyl or mefenoxam treatment. Even with resistant varieties, I recommend a treatment as fields with Phytophthora generally also favor Pythium.

The most common fungi involved in seedling diseases in Nebraska are species of Fusarium, Phytophthora, Pythium, and Rhizoctonia. All four are capable of killing soybean seedlings or at least causing sufficient damage to affect the plant's ability to achieve full yield potential. Remember that fields with a history of Phytophthora should be planted to a resistant variety. Fields with a long-term history of Phytophthora may require a different resistance gene if you are noticing Phytophthora-killed plants when you grow resistant varieties. In addition, fields with a history of Phytophthora will require additional levels of mefenoxam or metalaxyl chemistry above the standard rate. See the UNL Extension publication, Management of Phytophthora Root and Stem Rot of Soybean.

If you are not sure which seedling disease problem you had previously, a combination product is a good choice. Most combination products will have activity on Pythium as well as Fusarium and Rhizoctonia. The best approach is to identify the problem and keep notes on the field to match the disease problem with the best treatment.

Loren J. Giesler
Extension Plant Pathologist