You also must select seed treated with the right chemicals to control seedling diseases. Several fungi can cause seedling diseases and different fungicides are effective for different fungi. Two or three fungi often can be found in the same field. Usually a field contains only one dominant pathogen, so select chemicals that target the dominant fungus. If you do not know which fungus is causing stand reduction in your fields, target Rhizoctonia , Pythium , and Phytophthora , which account for 90 percent of seedling diseases in Iowa.
Some chemicals contain several compounds that are effective on all three fungi.
Pythium and Phytophthora are closely related, and most chemicals have the same efficacy for the two fungi. Pathologists in Ohio have conducted seed treatment experiments for many years because of seedling disease problems in that region. The following table shows the relative efficacy of various chemicals in controlling seedling disease pathogens in Ohio. These recommendations are applicable to Iowa because they are based on experimental results generally consistent with many other states, including Iowa. Relative efficacy of seed treatments for control of soybean seedling diseases.