Looking Below the Surface
This article was originally published on June 14, 2012 and expired on July 14, 2012. It is provided here for archival purposes and may contain dated information.
Do you have a corn nematode
problem? Is your nematicide doing any good?
According to Plant Diagnostic
Clinic and IPM coordinator Suzanne Bissonnette, unexplained yield losses or
patchy areas of low productivity or vigor may indicate not a herbicide,
nutrient, or environment issue but an established corn nematode population. A
2009-2010 survey supported by the U of I National Institute of Food and
Agriculture-Extension Illinois Pest Management program showed that corn
nematode populations were a bigger issue than had been previously thought.
Corn nematodes include a number
of damaging species, such as dagger, lance, lesion, ring, stunt, and
occasionally, spiral nematode, which may be found in heavy soils.
situations require different types of product application, so it is best that
you send in a sample for analysis before attempting nematode control," said
Bissonnette. "You have no other way of knowing what your initial
population is or if the population is being controlled."
The survey found that about half
of the cornfields in Illinois have lesion nematode populations with densities
at or above the threshold for moderate to severe risk of injury (yield loss).
Lesion nematodes are not only capable of injuring corn roots, but they also
frequently act as vectors for the development of root rots.
It is not true that corn
nematodes are a problem only in very sandy soils. Sandy soil is a risk factor
for only a few species (needle, sting, and stubby-root nematodes throughout
Illinois, and southern root-knot nematode in southern Illinois). Although
needle nematode can kill corn seedlings, most nematodes will not cause severe
injury unless the infestation level is very high.
Bissonnette said, "Consider
sampling for nematodes now, especially in corn fields that are at risk."
Some risk factors include corn-on-corn growing, minimal or no tillage, and the
absence of nematode-suppressing soil-applied insecticides. The best time to
sample for nematode diagnosis is approximately 4 to 6 weeks after planting. The
pest management strategy depends on the species involved and how high their
numbers are, so it is very important to get a good sample.
Start by examining the physical
characteristics of the plants: If there are no symptoms (hot spots) in the
field, sample a representative area of the field, perhaps 10 acres or less.
Sample in a zigzag or "w"-shaped pattern, and collect 20 to 25 cores
in a bucket. If there are hot spots, sample around their edges, not in the
centers, and collect a total of 20 to 25 cores. Record the GPS coordinates for
Sample as deeply as possible
from within the rows when the soil is moist but not wet to a depth of at least
6 to 8 inches. Use a 1-inch-diameter soil probe if possible.
Treat the samples gently because
some corn nematodes are very sensitive to manipulation, and it is important not
to kill them before they reach the lab. Do not break up the cores or drop the
samples. Put the samples in a plastic rather than paper bag to help preserve
moisture during transport, and store them in a cooler. Include the GPS
coordinates for the samples along with contact information when submitting
Symptoms of corn injury caused
by nematodes look similar to those caused by other production problems,
including poor or uneven crop development, yellowing or streaking, and reduced
or brushy root systems. The only way to diagnose corn nematode is by direct
examination under a microscope following an appropriate extraction method.
U of I Plant Clinic nematologist
Alison Colgrove and her staff test soils for nematodes. Services include soil
nematode analysis $40.00, root analysis $40.00, soybean cyst nematode (SCN) egg
counts $20.00, pinewood nematode $20.00. Send samples to the Plant Clinic, 1102
S. Goodwin, S-417 Turner Hall, Urbana, IL, 61801. For specialty testing,
including SCN Hg typing, variety screening, phytosanitary testing, or other
nematode projects and diagnostics, contact Colgrove at email@example.com or 217-333-9057.
More information regarding nematode sample submission can be accessed on the
Plant Clinic website at http://web.extension.illinois.edu/plantclinic/.
Source: Suzanne Bissonnette, Plant Diagnostic Clinic and IPM coordinator, firstname.lastname@example.org
Pull date: July 14, 2012