4 minute read
Pushing Back Against Field Resistance
This year, I was asked to go visit a farmer who was experiencing a problem with his soybean field. The field was showing signs of nutrient deficiency, which could be a result of many things. So I asked him if he had ever tested for soybean cyst nematode (SCN). He proudly told me that his farm was one of the first fields tested and found to have SCN in the 1970s, when this pest was first introduced to Illinois. The problem is that he knows that SCN is in his fields, but he and 80 percent of soybean farmers today who have this pest have not had to worry - until now. That's because after SCN was established within the Midwest, university breeders developed resistant varieties to effectively combat SCN. Most of the soybean varieties sold today consist of the same resistance (PI 88788). In turn, many farmers feel that SCN is one less pest that they must worry about in their soybeans.
The reality is that the SCN, or Heterodera glycines (HG), has adapted to this resistance. This did not just happen overnight but has evolved and worsened over the past 30 years. This means that SCN could be reproducing on resistant varieties, which is allowing the pest to continually build in numbers across many fields. Based on a recent study by the University of Illinois, our state’s most common HG type is 2.5.7. This means that these populations can reproduce on the following sources of resistance: PI 88788, PI 209332 and PI 548316. In fact, 100 percent of the populations in that study could reproduce on PI 88788, the primary source of resistance to SCN, highlighting that we are losing an essential management tool.
This is why we now recommend to farmers, like the one I just visited, to test again for SCN to get a handle or a baseline of current SCN populations within their fields. Signs of SCN are not easily identifiable, and there can be significant yield lost without any obvious above-ground symptoms. Current monitoring methods tend to lack accuracy and efficiency, and crop damage thresholds are difficult to establish. When scouting in the field, look for stunting and yellowing in soybeans. Root stunting, discoloration, and fewer nodules are potential below-ground symptoms of SCN. Collecting a soil sample is key to seeing if SCN is present in your field.
The Illinois Soybean Association (ISA) has partnered with the University of Illinois by providing free SCN (egg count) soil sampling. Farmers can scan the QR code for more information, or they can email freeSCNtesting@illinois.edu to request a free SCN kit with instructions and a prepaid shipping label. Allow the university's Plant Clinic a few weeks to analyze your soil sample for SCN so they can provide you with an accurate summary of results. Gathering data from across the state is crucial to identify exactly where SCN is attacking and to quantify its impact on soybean crops. This research will lead to new ways to overcome resistance in the field.
Currently, if you do test for SCN and find that you have high populations in a field, some might say to try to find a soybean variety with an alternate source of resistance. Today, that is easier said than done. There are a few soybean varieties that consist of Peking resistance, but often these varieties might be too early in maturity or not the right fit for your farm. The second most important management strategy to combat SCN is at least a two-year rotation with a non-host crop such as corn to help deplete SCN populations. Seed treatments are a third management tool but only affect the first wave of juveniles that attack the roots and do not provide season-long protection.
We need a multifaceted approach to combat SCN but also want to look at other management tools such as cover crops and methods to pinpoint the pest in fields. Southern Illinois University (SIU) Research funded by ISA, "Assessing the Impact of Cover Crops on SCN Populations in Field Conditions - ILSoyAdvisor," is helping us gain a deeper understanding of cover crops and their potential to mitigate damage caused by SCN. Another multi-year research project conducted by SIU, "Using Multispectral Platforms to Manage the Soybean Cyst Nematode - ILSoyAdvisor," funded by ISA, has already discovered that drone-based remote sensing provides cost-effective, reliable monitoring of SCN damage. For further research updates, go to ILSoyAdvisor.com/learn.
