We recently participated in a Soybean Cyst Nematode (SCN) Summit hosted by Syngenta.  Most of the Extension Nematologists in the Midwestern US were in attendance.  SCN remains the single largest yield-limiting disease in soybeans, accounting for billions of dollars of losses annually.  Our nematologists are now sounding the alarm on an emerging and very serious new problem with SCN. 

Today, 98% of commercial soybean varieties derive their genetic resistance to SCN from the same source, PI88788.  In essence, the industry has placed nearly all of our genetic eggs in the same basket, and for good reason. PI88788 has provided SCN resistance while not compromising yield potential.  The problem we now face is that SCN populations in soil samples submitted from throughout the Midwest soybean belt are demonstrating the capability to reproduce on PI88788.  Resistant varieties by definition do not allow more than 10% female SCN reproduction on their root systems.  Many of the samples now coming into diagnostic laboratories are showing anywhere from 20% up to more than 50% reproduction on PI88788.

This means that SCN populations are biologically adapting to thrive on our best genetic tools to combat them.  Resistant populations emerge through natural selection, and the process is accelerated when the same selective pressure is applied repeatedly.  In this case, we planted only one source of genetic resistance over and over again, gradually building up SCN populations that were able to survive on those varieties.

So what can be done?  The same best management practices apply to SCN that have always applied.  First, take the test to beat the pest – soil sampling is the only way to know the magnitude of the problem and the characteristics of the SCN population in your soils.  Second, rotate to non-host crops like corn, wheat, and alfalfa to suppress SCN reproduction.  Third, control alternate host weeds like the winter annuals purple deadnettle and henbit.  Fourth, rotate to a different PI88788 variety with inherently better SCN resistance ratings. 

In addition, some new and very effective seed treatment tools are now available to shore up PI88788 until new genetic tools are developed.  Clariva from Syngenta offers a biological mode of action called Pasteuria nishizawe that provides full-season protection against SCN.  Bayer CropScience offers a product called ILeVO with the active ingredient fluopyram, which provides 45 days of nematicidal activity and protection against sudden death syndrome. 

We conducted trials with both products in 2015 and found large yield response potential when the products are placed in high risk scenarios with elevated SCN numbers, resistant SCN populations, susceptible varieties, and environmental conditions favorable to disease development.  I encourage farmers to consider trying these tools in their production systems in 2016.

By: Tim Laatsch, Insect and Plant Disease Technical Manager