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Soybean Cyst
Nematode (SCN)
Compliments of
Agronomy Services Department
Soybean cyst nematode (SCN) is a severe
problem throughout soybean growing areas, causing yield losses as high as 50% in some
fields. The earliest symptoms are often poor soybean growth or an unexplained reduced
yield. The visual symptoms associated with this nematode can easily be confused with
herbicide injury, poor drainage, plant diseases, drought stress or nutrient deficiencies.
Evidence of SCN is often compounded when one of these stresses is already present.
Check root
system
for adult
SCN females
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The life cycle of the SCN,
from egg to egg, takes 21-24 days under optimum conditions
(75-82� F). Therefore, several generations are possible throughout the growing season.
With each female capable of producing 200-500 eggs, the SCN population can grow rapidly
every year soybeans are raised in a particular field. Although the population can be
reduced as much as 55% each year a non-host crop is grown and remains free of host weeds,
the population will grow in a stair-step fashion in a corn/soybean continuous rotation.
To determine if your fields
have SCN at economic-threatening levels, have a soil sample analyzed. Collect many samples
at a depth of 3-4" from within the field, combine them, mix thoroughly and take a
sub-sample of approximately one pint. Label the sample with name, address, county where
sample was taken, date, and send to your local lab. Do not let the sample sit around for
any length of time. Nematodes may succumb without a proper food source, leaving you with
an impression of a lower population. Many University labs are analyzing samples for free
or at reduced charge, compliments of the Soybean Board.
Fall is the best
time to sample
soil for SCN.
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The recommended
crop rotation sequences for reducing soybean cyst nematode to a sub-economic level are as
follows: based on a low to medium population - 3 years without a host crop; for high
population - 5 years without a host crop; for very high populations - 7 years without a
host crop. SCN resistant varieties are included in the non-host category. Some of the host
crops and weeds that SCN thrive on include soybean, garden bean, lespedeza, henbit and
common mullen. There are some crops and weeds that SCN can live on but not grow or
reproduce as rapidly including, hairy vetch, canola, sweet clover, alsikeclover, red
clover, wild mustard, common chickweed and pokeweed.
SCN is not a pest to fear, but
to manage through prudent crop rotation. Since one genetic line (PI88.788) is used in over
90% of the resistant varieties of soybeans grown throughout the corn belt, rotating forms
of resistant varities is not practical. Rotating varieties utilizing the same line is a
more practical solution. New forms of resistance or immunity are targeted to be released
in a few years. Some of these include either GMO or non-GMO forms.
A common question often asked
is "Are there any nematicides that are effective against SCN?" The answer is
yes, but they are not economical to use. Nematacides are very expensive and only provide
protection through part of the season. After the nematacide has degraded, the SCN will
thrive on the healthy plant, often resulting in a higher nematode population at the end of
the season than before treatment was started.
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