The use of seed treatments on soybean has increased in the last few years in Illinois. Some companies are now offering their own proprietary treatments, and a few new treatments are available. Commonly used seed treatments along with their active ingredients are listed in Table 1.
Fungicide seed treatments for soybeans can be used to help ensure good emergence and uniform stands, but they may not always result in a yield advantage. In general, there are two reasons to treat soybean seeds with a fungicide: if poor-quality seed is being planted, and to protect against seedling diseases.
It is always recommended that the highest-quality seeds be planted, but this practice is not always possible. Fungicide seed treatments may be able to help improve stand establishment of a variety with poor-quality seed. This is especially true if the reduced quality is due to infection by a fungal seedborne pathogen. If the poor quality is the result of mechanical damage, a fungicide seed treatment will not increase the germination rate of the seeds, but it may help provide a more uniform stand.
Seedling diseases of soybean can be caused by pathogens such as Pythium, Phytophthora, Rhizoctonia, and Fusarium. In some cases, a complex of these pathogens may affect soybean seedlings. Fungicide seed treatments can be effective in protecting seeds and seedlings from these pathogens for a short period, which may allow seedlings to become established and be productive plants. The risk of being affected by seedling diseases may increase when planting into cooler soils (typically observed in late April and early May) and when planting into a field with a history of seedling disease problems.
University of Illinois soybean seed treatment trials conducted from 2005 to 2010 across several locations (Figure 1) showed that the average yield response to fungicide seed treatments was 0.3 bu/A; however, there is a general trend for yield responses to increase when fields are planted earlier into cooler soils (late April to first week of May)