Sampling Corn Fields In Autumn For Nematodes
LEXINGTON, KY.
Nematodes are microscopic roundworms
that attack roots of corn and
other plants (Fig 1.). In corn, nematodes
affect yield by damaging the root
system. They become more important
when there are other root-related
stresses in the same field, such as moisture
shortage, root damage from insects,
or compaction.
There is increasing interest in nematodes
that attack corn, for several reasons:
1. In the past, soil-directed
organophosphate and carbamate insecticides
gave some secondary suppression
of nematodes. Currently, more selective
insecticides, and Bt corn for corn rootworm
control, don’t provide secondary
suppression of nematodes.
2. The increase of no-till production
can favor certain nematodes that are
sensitive to tillage (needle and dagger
nematodes).
3. More corn-following-corn also favors
the needle and dagger nematodes.
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 best way to
determine whether nematodes
may be affecting
yield is to sample for nematodes.
While winter
temperatures will cause
some nematode mortality,
sampling in the autumn
after crop maturity gives a
producer time to react to
findings, by obtaining
seed treated with Avicta®
seed treatment or considering
an alternative crop.
For sampling in the autumn,
use a soil probe
and sample within the
row – that’s right, within
the row. This is different
from sampling for soil fertility.
Sampling within the
row allows you to get a
count of destructive endoparasitic nematodes
(lesion and lance nematodes),
because many of those adults leave the
root as the crop dries down and the roots
die. Sample when the soil is moist but
not wet. Walk a zig-zag pattern, and take
20 cores to a depth of 12 inches. Gently
mix these cores in a container. Don’t let
them dry out or be subjected to temperature
extremes before mailing as soon as
feasible to a nematode laboratory.
Laboratories that can analyze nematodes
in soil samples collected at this
time of year include:
• Purdue University, http://extension.entm. purdue.edu/nematology /cv/submissionform.pdf
• Mississippi State University,
http://msucares.com /pubs/misc/m1230.pdf
• University of Florida,
http://edisifas.ufl.edu/sr011
• Iowa State University,
http://www.extension.iastate.edu/Publications/PD32.pdf. Δ
DR. PAUL VINCELLI: Extension Plant
Pathologist, University of Kentucky