Begin Scouting For Soybean Cyst Nematode

It is that time of year again for me to talk about soybean cyst nematode. While driving to Purdue University in West Lafayette, Indiana early last week, Terry Anderson (AAFC- Harrow) and I noticed a large number of fields that were displaying typical SCN symptoms.

Our comment at the time was that it would not be long for those same symptoms to show up in Ontario and it wasn't. SCN symptoms are showing up in the traditional areas of southwest Ontario plus in newer areas such as the Princeton area (thanks to Leanne Freitag, Cargill). Symptoms have accelerated this week primarily due to the dry conditions and the early spring we experienced.

The spring allowed the nematode to begin development early and the dry conditions have been good for SCN reproduction. The return to more seasonal temperatures will help the nematode.

Growers need to scout their fields and dig-up plants. Pay particular attention to fields where the plants are stunted and/or the stands tend to have an uneven or wavy appearance. Affected areas are commonly oval or elliptical that increase in size annually and often elongate according to the direction of tillage or soil texture patterns of the field. The leaf margins of infected plants are yellow and may resemble nitrogen, manganese or potassium deficiencies. The root systems of infected plants are usually poorly developed and discoloured due to secondary invaders (root rot organisms).

In addition, the roots have a reduced number of functional nitrogen fixing nodules. Symptoms are more pronounced when soybeans are under stress from dry conditions, soil compaction or low soil fertility. Symptoms often show up in stressed areas of the field or entry ways / field boundaries (infested soil). Keep in mind though that the most common SCN symptom - IS NO SYMPTOMS!

Figure 1. SCN Cyst on Soybean Roots

The lack of symptoms is particularly true when the crop is growing vigorously. The above ground symptoms I described earlier often disappear under good growing conditions so don't be surprised if this occurs when we get a good rain. The fact that SCN damage can go under the radar is one reason why many growers are unaware they have a SCN problem until yields are affected significantly.
Therefore be proactive! Get out and enjoy the cooler temperatures and don't forget to dig up those soybean plants. Examine them for the small white to yellow cysts (pin-head size). This is still the best method to detect SCN.

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