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Issue No. 2, Article 6/April 9, 2010

Fungicide Seed Treatment Considerations for Soybean

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 potential reasons to treat soybean seeds with a fungicide: when poor-quality seed is being planted, and to protect against seedling diseases.

Poor-quality seed. It is always recommended that the highest-quality seed be planted, but this is not always possible. Fungicide seed treatments may help improve stand establishment of a variety with poor-quality seed (Figure 6). This is especially true if the poor quality is due to infection by a fungal seedborne pathogen. If it is due to mechanical damage, a fungicide seed treatment will not increase the germination rate of the seeds, but it may help in providing a more uniform stand, which could (but does not always) translate into greater yields.

Figure 6. Effect of fungicide seed treatments on germination of a soybean seed lot infected with both Sclerotinia sclerotiorum and Phomopsis longicolla. Data courtesy of Carl Bradley, University of Illinois.

Protection against seedling diseases. 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 the seedlings to become established and be productive plants. The risk of being affected by seedling diseases may increase when planting early (April to early May), when planting into a field with a history of seedling disease problems, and when weather conducive for seedling diseases (generally cool and wet) appears just after planting. A summary of University of Illinois soybean seed treatment trials conducted from 2001 to 2008 shows that the average increase in yield obtained with a fungicide seed treatment was 0.8 bu/acre; however, the yield advantage increased when fields were planted earlier (late April to first week of May; Figure 7).

Figure 7. Summary of University of Illinois fungicide seed treatment trials on soybean from 2001 to 2008. (Trials in 2001 to 2006 were conducted by Dr. Wayne Pedersen; in 2007 and 2008 trials were conducted by Dr. Carl Bradley.)

Which product(s) should I use? If you decide to use a seed treatment on soybean, it is important to use products that provide broad-spectrum control of many pathogens. The treatment should include either mefenoxam or metalaxyl as the active ingredient, which provides some protection against oomycete pathogens (Pythium and Phytophthora). The treatment should also contain at least one other fungicide (i.e., fludioxonil, trifloxystrobin, pyraclostrobin, ipconazole) that will provide broad-spectrum control against Fusarium and Rhizoctonia.--Carl A. Bradley

Carl A. Bradley

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