March 19, 2010

The current forecast is for a wet spring with wet conditions at planting. Given this, soybean seed treatment fungicides may be a good choice in 2010, especially for early planting dates.

Pythium and Phytophthora are two very common seedling diseases affecting soybeans in Nebraska. Of the two soybean diseases favored by wet conditions, Pythium is the most common and is sometimes referred to as “white mold” on plants.

The problem with managing any seedling disease is that you need to select the appropriate fungicide treatment before you put the seed in the ground.

Consider the following factors and if you have any of these conditions, use a seed treatment fungicide for your soybeans.

• Field History of Seedling / Emergence Problems. Ideally you have identified the disease and can match the correct treatment. If not, use a good combination product.
• Early Planting. If you’re considering early planting, fungicide seed treatments are a necessity. Cool, wet soils are conducive to the development poor stands. No-till fields will have cool soils later in the season than fields receiving some tillage. These will more commonly have seedling disease problems.
• Phytophthora History. Fields with a history of Phytophthora will need additional metalaxyl or mefenoxam treatment. Even with resistant varieties I recommend treating for Phytophthora which will favor Pythium and in some instances and you may have purchased the correct resistance source.

Most seed companies offer a standard treatment, but in many instances this will not be sufficient for a field with Phytophthora. Based on your field history, if you know the disease you are trying to control, check with your seed salesman to ensure that you have a good match in your fungicide.

Note: All references in this article to seed treatment apply only to the use of seed treatment fungicides and are not intended to be applied to seed treatment insecticides.

Resources

For more information see:

• NebGuide G1852, Seed Treatment Fungicides for Soybeans, which is currently being updated
• NebGuide G1785, Management of Phytophthora Root and Stem Rot of Soybeans, for information on product rates and management of Phytophtora

See the Crop Watch Soybean Disease Management and Plant Disease Central Web sites for further information on crop plant diseases.

Loren Giesler
Extension Plant Pathologist