Soybean seeds and seedlings are susceptible to a number of pathogens lurking in the soil, waiting for the right conditions.

These pathogens include Pythium, Phytophthora, Rhizoctonia and Fusarium species. In North Dakota, soil conditions can turn wet and cold overnight. Under these cool (less than 60 degrees) and wet soils, the soybean seeds will germinate and emerge very slowly, making them more susceptible to attack by seed and seedling pathogens.

Fungicide seed treatments might be a valuable tool to use to protect soybean seeds and seedlings against diseases. Research conducted in multiple years and locations (14 total environments) by Carl Bradley, North Dakota State University Extension Service plant pathologist, shows that there may be an overall benefit using seed treatments on soybeans.

“The biggest benefits were observed in years and locations where soil conditions turned wet and cool after planting,” Bradley says. “In years and locations where ‘big’ benefits were not observed, the seed treatments, generally, paid for themselves.
Averaged over all 14 environments in the study, the net return with the use of seed treatments ranged from $10 to $20 per acre compared with untreated soybeans, depending on the product used.”

Under certain soil types, management practices and field histories, the probability of getting a benefit from a seed treatment probably increases. These conditions include:

• Heavy clay or poorly drained soils
• No-tillage or reduced-tillage
• Early planting
• Tight crop rotations
• Disease history of the field

“When choosing a fungicide seed treatment, choose a product that contains either mefenoxam or metalaxyl,” Bradley says. “These chemicals protect against Pythium and Phytophthora. The product also should contain at least one other chemical, such as fluidoxonil, azoxystrobin or others, that will protect against Fusarium and Rhizoctonia.”

In general, most “newer” seed treatment products are safe on nitrogen-fixing Bradyrhizobium found in inoculants, but some products and formulations may be better than others.

For more information about specific seed treatment products, check the 2006 North Dakota Field Crop Fungicide Guide available through the NDSU Extension Service, as well as the NDSU Extension Plant Pathology Web site.

Always read and follow manufacturers’ label directions.