Sometimes we forget that the most yield improvement may well be made by dealing with our endemic pest problems. I'm talking in particular about Soybean Cyst Nematode (SCN). Our chronic yield losses from this pest have not gone away. In Illinois over 80% of the fields are infested with SCN. Managing this pest with the right selection of a SCN resistant variety in affected fields and then following up with timely monitoring is definitely in your best interest.

So, most of the soybean farmers in Illinois have a SCN infestation, but the situation may not be what is commonly perceived. They know, for example, that when SCN numbers are high, plants are stunted, yellow, and yield poorly. They know that planting SCN-resistant varieties will help them recover yields and maybe reduce SCN levels. But how many farmers with SCN-infested fields know that SCN can reduce yields by 30% or greater without causing any stunting or yellowing. How many farmers know how SCN is affecting their ability to manage other problems in soybean fields, such as weeds, insects, and disease-causing pathogens? SCN is a disease that can be managed but it takes some pre-planning, proper seed selection and the additional step of monitoring.

Our U of I Extension Nematologist Dr. Terry Niblack details three reasons why soybean fields need to be sampled regularly. First, even if you have a field currently free of SCN the state infestation rate is expected to move from 80% to 100% of the fields within a decade. So you need to know if and when it shows up to be able to get ahead of the curve in managing the pest.

Next, Dr. Niblack notes that it is much easier to maintain low SCN population numbers in a field than to have to reduce the population from way too high to low. We need to recall that up to 30% yield loss can occur without visible above ground symptoms, and testing the soil is the only way to determine what the population is doing.

Third, even if you have been managing SCN through the selection of SCN resistant varieties, the population still needs to be sampled and monitored. The nematode can reproduce even on SCN-resistant varieties and an increase in SCN population in a managed field would indicate that the current population has been able to overcome the resistant genes being used in your current varieties. You need to know if you have to change your variety selection to utilize SCN resistance genes to mange the adapted population.

A soil sample should be a composite of 20 or more cores taken in a zigzag pattern across a field. One sample can adequately represent a 5-acre area. That may seem daunting, so, what do you do if the field is 300 acres? Niblack recommends collecting samples from two or more arbitrarily selected 5-acre sections that represent similar soil types and crop histories. There's no need to sample the entire field unless you're planning to plant different varieties in different sections of the field. Excellent instructions for sampling are available at http://www.planthealth.info/scn_scout.htm.

Your samples can be sent to a private nematode testing lab or to the University of Illinois Nematology Lab, Department of Crop Science, AW101 Turner Hall, Urbana, IL 61801. Two types of testing can be done. First, a standard population count. This tells you if you do have the nematode and how high that population may be in the field. A second kind of test can also be performed called an HG type test. This test is not necessary for everyone. If a producer has been managing SCN but just doesn't seem to be making any progress against it then that's who would benefit from an HG Type test which will characterize the actual population in the field.

Advances in the understanding of SCN have led to several important refinements in how to detect, monitor and manage SCN in your fields. Taking these steps will take some of the pest risk out of this year's soybean crop.