Many of us say “SCN” like we were spitting and with good reason. Soybean Cyst Nematode remains a thief of yield potential in many soybean production fields across the state, and in spite of our efforts, seems to continue to expand in territory. While we can begin looking for live SCN females attached to soybean roots about five weeks after planting, this is the time of year where field counts are usually highest and thus easiest to identify as problems.
Above ground symptoms are exacerbated by drought stress as the root system becomes stunted by SCN often accompanied by fewer nitrogen-fixing nodules. Symptoms may include stunted growth, yellowing, and symptoms of early maturation. In fields where you know you have SCN populations that can promote these symptoms, now is the time of year to do pre-harvest field surveys and gain a better understanding of the cause of what you actually see in those individual fields this year.
Anecdotal evidence in research suggests that even low level soybean aphid pressure promotes greater SCN egg numbers. While research to prove this definitively is still ongoing, if you have fields where aphid pressure has been particularly high this year, an SCN survey there might have greater importance for next year rotation and planting decisions.
We are approaching the season where pressure to make seed decisions for next year begins. In that light, and before the serious pressure of soybean harvest begins, use the information from your field surveys to prepare for how your fields will be planted next year. Remember to consider the cultivars you plant with SCN resistance and rotate both the cropping system and the SCN resistance mechanisms you utilize. Over use of the same resistance mechanism will increase the potential of pests like SCN to overcome that genetic combination further limiting your options for yield potential in future years. As you look at planning for next year, here is another consideration pointed out by Bruce Potter, University of Minnesota IPM Specialist at SWROC during a field day this summer. Bruce suggested that if you had drowned out areas in a corn field this spring and came in once they dried out and planted soybean you’ve lost your SCN crop rotation effect. The balance of recovering income potential on acreage and continuing a host cycle for a soil born pest must enter into your total management plan for each field. The severity of the SCN problem in individual fields must be considered in future years if a drowned out event occurs in terms of what you plant back in those flooded out areas. Finally in your field management decisions, consider that even though the current soybean crop is at R4-R5 in most areas and we are moving toward the end of another season, weeds such as chickweed, purple dead nettle and milk vetch serve as a host for SCN until frost. If your field has prevent plant or drowned out areas where planting anything was not possible, those weeds can also support SCN populations.
For some good news, the research supported by the soybean check off continues and I’d like to give you an update on one of our SCN projects lead by Dr. Nevin Young at the U of M. Dr. Young’s project in concert with Dr. Jim Orf is using molecular and traditional breeding to improve genetic resistance in soybeans adapted to Minnesota. Dr. Young’s first quarter report for this year indicates that they 70 different SCN resistant parents in field crossing blocks to combine SCN resistance with other essential traits including high yield, aphid resistance, SDS resistance and IDC tolerance to name a few. His laboratory is also evaluating a large pool of lines using marker-assisted selection to screen for new genetic resistance combinations and is projecting a release rate for three new cultivars per year with SCN resistance mechanisms. Current lines Dr. Young’s lab is evaluating involve crosses from about eight additional resistance sources as a result of materials provided by Dr. Senyu Chen’s SCN research to find novel SCN resistant and tolerance genes. All of this is exciting progress and the result of the Production Action Team composed of soybean farmers directing your check off dollars in research to ultimately put more soybeans in your bin. We are all working together to continue to offer Minnesota soybean farmers the best pool of options against yield robbing problems such as soybean cyst nematode.