Damping-off diseases are a major concern for early-planted soybean. Because more and more growers are planting early, there is more interest in using seed treatments to promote good stand establishment.
Treating seeds with fungicides may be beneficial under the following conditions:
1. Early planting in cold, wet soils
2. Reduced till and no-till fields
3. Seed with low germination rate (<80%) or low seed vigor
Several kinds of fungi cause seed rot, seedling rot (damping off) and seedling disease. The most common ones in Iowa are Rhizoctonia and Fusarium, the water mold fungi Pythium and Phytophthora, and seed-borne Phomopsis.
The active ingredients mefenoxam and metalaxyl are effective in controlling the water molds Pythium and Phytophthora . When either one of these two chemicals is mixed with other active ingredients, the formulation can be used to control the other soil-borne fungi in addition to Pythium and Phytophthora (Table 1). We initiated an evaluation of fungicide seed treatments in 2004 and will continue in 2006.
For a good description of soybean seedling diseases, read Soybean Seedling Diseases in the Integrated Crop Management newsletter.
Table 1. Specific activity of fungicide seed treatments
| Active Ingredient | Trade names | Pythium | Phytoph- thora | Rhizoctonia | Phomopsis | Fusarium |
|---|---|---|---|---|---|---|
| metalaxyl | Allegiance formulations | excellent | excellent | no activity | no activity | no activity |
| mefenoxam | Apron formulations | excellent | excellent | no activity | no activity | no activity |
| azoxystrobin + metalaxyl | SoyGaard | good | poor | good | good | good |
| captan | many formulations | good | poor | good | fair | fair |
| captan + PCNB +thiabendazole | Rival | poor | poor | good | excellent | excellent |
| captan + PCNB + metalaxyl | Rival Pak | good | good | good | good | good |
| carboxin + thiram | Vitavax-200 | poor | no activity | fair? | excellent | poor |
| carboxin + thiram + metalaxyl | Stiletto | good | good | good | excellent | poor |
| carboxin + captan | Vitavax-captan | fair | poor | good | good | fair |
| fludioxonil | Maxim 4FS | poor | poor | good | good | good |
| fludioxonil + mefenoxam | ApronMaxx formulations | good | good | good | good | good |
| PCNB + ethazole | Terraclor Super-X Terra-Coat L-205N | good | poor | good | no activity | poor |
| thiram | many | fair | poor | good | fair | fair |
Insecticide Seed Treatments
High numbers of bean leaf beetles have created a concern about direct losses from beetle feeding injury plus losses related to bean pod mottle virus. Previously, we have been able to manage the beetles using foliar insecticides, but we do now also have an insecticide seed treatment that can be used to manage the beetles. In 2004 and 2005, Cruiser and Gaucho were registered to use as a seed treatment on soybean in United State, respectively. They are both systemic insecticides and belongs to a new subclass of neonicotinoids. They moves systemically throughout the plant and protects against target pests through contact and stomach activity. We are evaluating both Cruiser and Gaucho in different trials in combinations with different fungicides. The largeste study will be finalized after the 2007 growing season and data will then be available.