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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.
