South Dakolta, USA
May 12, 2016

Source: iGrow
Written collaboratively by Jonathan Kleinjan, Febina Mathew, and Adam Varenhorst.

Seedling blight of soybean

Early to mid-May temperatures for South Dakota are forecast to be cooler than normal. These cool temperatures, along with waterlogged soil in many areas of the state, set up favorable conditions for the development of certain soybean seedling diseases.

Fungicide Seed Treatments

Fungicide seed treatments can be effective at managing seedling blights and soybean root rots. Currently there are no soybean varieties available to growers with genetic resistance to the pathogens that cause seedling and root diseases such as Pithium root rot, Fusarium root rot, and Rhizoctonia root and stem rot (damping-off). While there are soybean varieties available with partial genetic resistance to Phytophthora root rot and sudden death syndrome, fungicide seed treatments can provide additional protection against these pathogens.

Insecticide Seed Treatments

Insecticide seed treatments target several above- and belowground early season insect pests. For soybean, the belowground insect pests include wireworms, seed corn maggots, and white grubs. The early season aboveground pests that insecticide seed treatments are labeled for include bean leaf beetle and grape colaspis beetle. In addition, some seed treatments are also labeled for soybean aphids. However, it is important to remember that insecticide seed treatments have a period of effectiveness that ranges from 20-40 days depending on environmental conditions and soybean aphids typically infest soybeans much later than this timeframe.

Soybean Seed Treatment Research

At this time, most soybean seed treatments are a package containing both fungicide and insecticide seed treatments. Ongoing research at SDSU is examining the efficacy of both the fungicide and insecticide components of a seed treatment package to determine which of these components is most important to protect soybean yields.

In 2015, a soybean seed treatment study conducted by Febina Mathew (SDSU) examined five different types of seed treatment packages on a commonly planted soybean variety at two locations. The soil at the Brookings location was heavy, somewhat poorly drained and the soil at the Volga location was well-drained and highly productive. The results from this study found up to an approximate 8 bu/acre response over the untreated check (Table 1).

Table 1. Effects of five seed treatment packages on soybean yield in two South Dakota testing locations in 2015.

Findings

The results in Table 1 show that seed treatments can provide varying levels of yield response in soybeans. This variation is most likely due to the different active ingredients present in the respective seed treatments. The 2016 South Dakota Pest Management Guide for Soybeans provides a summary of seed treatments, their active ingredients, and type of pest protection.

It is important to remember that while yield response to seed treatment was evident in these two locations in 2015, this level of response may not be evident in every location during every growing season. In some years and at some locations there may be no response to seed treatments. It is difficult to predict which seedling diseases and insect pests will be a problem from one year to the next. Seed treatments are particularly recommended if there is a concern about early-season soybean disease or insect pressure (for example, if a field has a history of root rot) or if a field has problems such as soil compaction or poorly drained soils. Treatments can also be useful to protect plant populations when growers use low seeding rates or plant soybean seed with a less than ideal germination rate.
For Further Reading

    Soybean Seed and Seedling Diseases. University of Minnesota Extension.
    Evaluation of Fungicide and Insecticide Seed Treatments on Soybean at Three Locations in Iowa in 2012. Iowa State University Extension and Outreach – Department of Entomology.
    Probability of Return on Investment with Using Soybean Seed Treatments. University of Wisconsin – Extension.

Website: http://www.sdstate.edu

Published: May 13, 2016