Sampling For Nematodes
LEXINGTON, KY.
April 24, 2012 – Nematodes are microscopic
roundworms that attack roots of corn and
other plants. In corn, nematodes affect
yield by damaging the root system and interacting
with opportunistic root-rotting fungi. They
become more important when there are other
root-related stresses in the same field, such as
moisture shortage, root damage from insects,
nutrient deficiencies, or compaction.
Although there is increasing interest in nematodes
as potential yield-limiting factors, the
threat these pose varies greatly from one field to
the next. The only way to determine whether nematodes
may be affecting yield is to sample for
nematodes.
When to Sample
The window at 4-6 weeks after planting is
probably the best time to sample, since the nematodes
will be in the root zone and the soil is
often moist enough to be able to insert a soil
probe. Plus, sampling early in the growing season
will give an idea as to whether nematodes
are likely to affect crop productivity. Summer
sampling is less than ideal. During summer, certain
nematodes (like the sting nematode and
needle nematode) move downward in the soil
profile, where the moisture is located. Also,
pulling samples from dry soil is difficult. Sampling
after harvest has its advantages, since it
gives a look at certain nematode populations,especially
endoparasites (lance nematode and
root-lesion nematode, which burrow within the
corn root), as well as the nematodes that go deep
into the soil during summer.
How to sample
The most important thing to realize is that
sampling for corn nematodes is different than
sampling for soybean cyst nematode. For
corn, sampling both soil and roots is advisable
for best results. Sampling guidelines
are as follows:
Sampling soil
• Instead of sampling at random or zigzag
pattern (like you would for soybean
cyst nematode), sample parts of the field
where yield losses or symptoms (stunting,
yellowing in elongated areas of the field)
are not explained by other factors, such
as soil compaction, soil type, etc. Corn
nematode populations can be extremely
variable (see Figure 1), so focus sampling
in problem areas of the field. However, if
some of the corn is severely affected, sample
from the edge of the damaged areas
rather than in the worst areas. It is important
to avoid badly damaged corn, because
corn nematodes require live roots to
feed on, and if plants are severely damaged
or dead, the nematode numbers will
be low.
• Make sure to sample within the row –
that’s right, within the row. This is different
from sampling for soil fertility. Take 20-25
samples.
• Sampling for nematodes in corn requires a
depth of at least 12 inches. This is much deeper
than for soybean cyst nematode. If sampling in
summer or fall, one may need to go as deep as
24-36 inches in order to detect sting nematode
or needle nematode (although these two nematodes
are usually found only in sandy soils).
• Put all 20-25 soil cores in a Ziploc bag. Don’t
break the soil cores, since some nematodes like
stubby root nematode are extremely sensitive to
soil disturbance. Label the bag with a permanent
marker (not a magic marker, which comes
off in water). Store samples in a cool, dry place
until shipment.
Sampling roots
Collect five to ten root masses from V6 plants;
the tops of the plants can be cut off and discarded,
and soil adhering to roots can be removed
as well. Roots can be placed in a plastic
bag separate from your soil samples.
Where to send samples
that can analyze nematodes in
soil samples include:
• University of Illinois,
http://web.extension.illinois.edu/plantclinic/
• Purdue University,
http://extension.enim.purdue.edu/nema/cv/submissionfor.pdf
• Mississippi State University,http://msucares.com/pubs/misc/m1230.pdf
• University of Florida,
http://edis.ifas.ufl.edu/sr011
• Iowa State University,
http://www.extension.iastate.edu/Publications/PD32.pdf Δ
DR. PAUL VINCELLI: Extension Professor and
Provost’s Distinguished Service Professor, University
of Kentucky