By Anne Dorrance, Extension Soybean Disease Specialist

This year’s early harvest provides the perfect opportunity to take a look at the SCN populations in your fields.  We know that the state is now “polluted” with SCN, but fortunately most of those fields are at very low levels — where they should be kept.  

However, there are some surprising locations where individual fields are getting or have gotten into trouble with very high populations. So let’s review the loss levels for SCN for the majority of soil types here.

If your SCN report in the past has come back as:

Not detected. This is not surprising. Remember that SCN sits in pockets and can be quite variable (Figure 1). Continue to monitor your fields.

Trace. May begin to measure some yield loss on susceptible varieties, especially on lighter soils.

Low. Plant SCN-resistant varieties or rotate to a non-host crop (corn or wheat). 

Moderate. Rotate to a non-host crop and follow with SCN resistant varieties the following year. We have planted susceptible varieties in fields with this level of SCN and have recorded 20-50% yield loss. 

High. Rotate to a non-host crop for 2-3 years, then sample SCN to determine if populations have declined to a level where soybeans can be planted again.

SCN is picky about what it feeds and reproduces on but it does like a few weed hosts and cover crops as well as soybean. If you have SCN in your fields, it is important to also control winter annuals such as purple deadnettle, but also avoid cover crops such as several of the clovers, cowpea and common and hairy vetch. 

SCN sampling is recommended in the fall because in most cases this is what the population will be in the spring. Warmer weather this year and hopefully no frozen ground should give ample time to collect and process the samples before spring planting. 

Processing of samples does cost time and money, so here are a few thoughts on how to sample or how to target your sampling to get the best information for your money. 

Through funds from the soybean check-off, we have completed several targeted surveys over the past 5 years. My group tended to target those fields where yields were stuck at or below 30 bushels per acre. Or when we sampled we hit those pockets in the field where the soybeans tended to be shorter or where they matured earlier and always yielded less that the rest of the field. We were able to detect SCN in almost all of these situations, so these are the ones that should have the top priority for sampling. 

Visit the Ohio State University website for updated information on where to send samples.