No. 3 Article 5/April 10, 2009

Considerations for Using Fungicide Seed Treatments on Soybean

Use of fungicide seed treatments on soybean seed is not currently the norm for Illinois producers, but it has increased in the past few years. Beginning with the 2009 season, seed of some varieties (such as all Monsanto Roundup Ready 2 Yield varieties) are being sold pretreated with fungicide treatments, which eliminates the producer's input on whether a fungicide seed treatment is needed and, if so, which product(s) to use.

For those who still have a choice, there are some factors to consider when deciding to use fungicide seed treatments on soybean. In general, there are two potential reasons to treat soybean seeds with a fungicide: if 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 be able to help improve the stand establishment of a variety with poor-quality seed. 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, but it may help in providing a more uniform stand, which could (but doesn't always) translate into greater yields.

In 2008, a field research trial was conducted at Urbana to evaluate the effect of fungicide seed treatments on a soybean seed lot with a low germination rate. In this trial, fungicide seed treatments did improve the yield compared to the untreated check. In addition, some seeds were run through the seed treater without being treated with a fungicide to determine whether running the treater had a detrimental effect. In this trial, there was no significant difference between untreated seed and seed run through the treater with no fungicide applied.

Effect of fungicide seed treatments on poor-quality soybean seed at Urbana, Illinois, in 2008.

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 of time, 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/A; however, the yield advantage became greater when fields were planted earlier (late April to first week of May).

Summary of University of Illinois fungicide seed treatment trials on soybean from 2001 to 2008 (trials through 2006 conducted by Dr. Wayne Pedersen; 2007 and 2008 trials 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 a product that provides broad-spectrum control of many pathogens. The treatment should include one of the active ingredients mefenoxam or metalaxyl, which provide some protection against oomycete pathogens (i.e., Pythium and Phytophthora). In addition, the treatment should contain at least one other fungicide (fludioxonil, trifloxystrobin, pyraclostrobin) that will provide broad-spectrum control against Fusarium and Rhizoctonia.--Carl A. Bradley

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