Soybean seed is increasingly costly, which makes getting a good stand the first time more valuable than ever. Seed rot and seedling diseases can make getting a good stand more difficult by reducing germination, emergence and seedling survival of soybeans, said Doug Jardine, K-State Research and Extension plant pathologist.
A good insurance policy for protecting stands and yields is to use a planting time fungicide seed treatment, Jardine said.
“K-State fungicide seed treatment evaluations have shown an average yield increase of two-and-a-half bushels per acre when a seed treatment was routinely used over the past eight years,” he said.
Jardine lists the following recommendations, which are based on more than 20 years of field research:
- All soybean seed planted before May 15 in eastern and central Kansas should be treated with a fungicide seed treatment. Where soybeans are being planted before May 15, it is especially beneficial to include products containing metalaxyl or mefenoxam for Pythium control.
- No-till fields planted before May 31 also should be treated.
- There is no K-State data on the effect of seed treatments in western Kansas, but irrigated soybeans in that region also should probably be treated with a fungicide seed treatment if planted before May 15.
- For soybeans planted in June or later, fungicide seed treatments only occasionally pay off.
Since it is difficult to know or predict what seedling diseases may be a problem in any particular field, Jardine said it is usually best to select a product that will give a broad spectrum of disease control, somewhat similar to tank mixing herbicides.
“Among the systemic fungicides used for soybean seed treatment, mefenoxam and metalaxyl are effective against Pythium and Phytophthora soilborne diseases. In addition, azoxystrobin, carboxin, fludioxonil, ipconazole, thiabendazole, trifloxystrobin and triticonazole are effective against Fusarium and Rhizoctonia soilborne diseases, as well as any of the seedborne diseases,” Jardine explained.
Several products have a combination of these ingredients to provide broad-spectrum control, he said. There also are some soybean seed treatments that combine fungicides and insecticides, he added.
There are some minor differences in the efficacy of each product against the various soilborne and seedborne diseases, he said. “But as long as you use a product that combines one fungicide from each of the two major groups of systemic products, as mentioned above, your soybean seed will be protected,” Jardine said.
If a rhizobial inoculant is to be used, check the product label for compatibility and specific instructions on usage, he added. Not all seed treatment fungicides are compatible, particularly some of the older materials, he noted.