Greetings! It is great to be serving the agronomic community of Illinois as the Extension Field Crops Plant Pathologist. My role at the University of Illinois at Urbana-Champaign (UIUC) is to help the producers of Illinois address field crop disease issues that impact productivity and profitability through applied research and extension outreach. Prior to my arrival at Illinois, I had served since 2013 as the Delaware and Maryland Extension Field Crop Plant Pathologist. I grew up in Wisconsin, and it is very exciting for me and my family to be back in the Midwest. I started at UIUC in November and my program will be very active in several areas of field crop disease management research, including soybeans this season, and I look forward to sharing information with you as the season progresses.
Every year, pathologists around the nation collect estimates of losses attributed to diseases in soybeans. You may not realize it, but soybean cyst nematode (SCN) remains the most important yield-robbing pathogen of soybeans in the United States. In 2015, over 109 million bushels of soybeans were estimated to have been lost because of this pesky roundworm. Often, however, these losses go unnoticed or are blamed on other issues.
Why might this be? Unlike foliar diseases or pathogens that produce toxins that move into the canopy and cause dramatic foliar symptoms (e.g., Brown stem rot, sudden death syndrome), SCN lives underground, infects root systems and drains nutrients from the plant. Under severe conditions, plants may appear stunted or become chlorotic because of SCN activity. However, many times foliar symptoms are not evident, and you may not notice any issues until you start looking at the yield monitor and wonder why yield is below expectations.
An important point about SCN is that once roots are infected, nutrients are sucked from the plant and your plant loses yield. The amount of yield loss depends on the numbers of nematodes that infect and feed on the soybean root system over the course of the growing season. A single cyst (female SCN) contains hundreds of eggs. Additional eggs are released from the female into the soil earlier in the infection process. Eggs from the cyst and soil hatch, and new females develop and infect roots.
Upon maturity the female turns into a cyst which, again, contains hundreds of eggs. Under ideal conditions the life cycle of SCN only takes about 4 weeks and multiple generations can occur during the growing season. You can imagine how only a year or two of this cycle can result in initial SCN populations that could be very damaging to soybean productivity. Understanding your SCN populations can help you tailor your management plan to minimize yield losses, determine if a management practice has been effective in reducing SCN, or help explain lower than expected yields. I will follow up on this point in future articles.
I typically recommend producers sample for SCN at the end of the season; however, samples can be acquired before planting if you were not able to sample in the fall. A good guide for sampling SCN can be found at the Tylka lab. Samples can be sent to one of several agricultural services in the state and region, as well at the University of Illinois Plant Diagnostic Clinic. Sample forms are available online as well as shipment instruction.