Soybean season is upon us and I have been asked about the effectiveness of seed treatments in soybean by several growers. Are seed treatments useful? As usual, the answer is, “It depends.” Fungicide seed treatments can increase the germination of poor quality seed if the low quality is due to the activity of a fungal pathogen or if seeds are planted into an environment that may delay germination (e.g. cold, wet soils). Poor germination caused by other factors (age, mechanical damage, etc.) will not improve with a fungicide seed treatment. Seed treatments can be viewed as insurance to ensure good seedling emergence, which is critical if you are using reduced seedling rates or you must plant poor quality seed.
In general, the profitability of seed treatments depends on seed quality and the weather conditions from the time of planting until about three weeks after emergence. The following table provides guidelines for the conditions when seed treatments may be useful and recommends some fungicides that can be used to control problematic pathogens. To avoid negative effects on nitrogen-fixing bacterial inoculants, add the inoculant to seed within 4 hours of planting or apply in furrow. Do not use fungicide treated seed for food, feed, or oil.
Table 1. Soybean Seed Treatments and Guidelines1
| Conditions | Active ingredients | Trade Name2 | Comments |
| Early planting into cold and wet soil (<65°F) | metalaxyl, mefanoxam, fludioxanil+mefenoxam | Allegiance FL™, Apron XL LS™, ApronMaxx™ | These fungicides target mainly Pythium damping off. Allegiance™ and Apron™ should be used in combination with other general use fungicide treatments such as captan or thiram. Similarly, the premix ApronMaxx™ can be used. |
| Fungal infested seed lot (germination 75-85%3) | Fludioxanil, captan, thiram | Maxim XL™, Captan-Moly™, Thiram™ | |
| Seed lot germination > 85%3 and normal planting conditions | No seed treatment required | ||
| Seed lot germination <75%3 | No seed treatment recommended. Do not use seed for planting if germination cannot be brought above 75% after cleaning the seed lot. |
1This table is partially reproduced from the 2013 Virginia Field Crops Pest Management guide published by the Virginia Cooperative Extension: http://pubs.ext.vt.edu/456/456-016/456-016.html.
2Fungicides mentioned here are illustrative and not intended as a product endorsement.
3Germination can be determined using a warm seed germination test: http://www.seeds.iastate.edu/seedtest/testing.html).