Greensboro, North Carolina
December, 2008
Source: Seeds of Progress -
Syngenta Seed Care
newsletter
Syngenta FarmAssist
What is a corn nematode?
Corn nematodes are microscopic, non-segmented roundworms that
appear in every soil type in every corn-growing county in the
United States. They are small and usually transparent, making
most species invisible to the naked eye. Corn nematodes are
obligate parasites that need a host species to feed, and they do
so using a stylet. The stylet enables nematodes to pierce corn
roots, gain entry to root interiors and inject enzymes directly
into the roots. The damage caused to corn crops by nematodes is
hard to identify and often misdiagnosed despite being widespread
and potentially very harmful. Damage from nematode attacks
presents itself with many different symptoms, and oftentimes,
there are no visible symptoms, but yield is impacted.
Symptoms of nematode attacks vary greatly depending on the type
of nematode feeding on the roots. None of the symptoms, however,
are exclusive to nematode pressure and therefore make diagnosing
nematode presence by symptoms alone nearly impossible. Growers
may notice above-ground symptoms such as small ears and kernels,
uneven tasseling and plant height, stunted plants, leaf
yellowing and thin stands when nematodes are feeding on corn
roots. Below-ground symptoms of nematode pressure include root
branching, lack of fine roots, root galling, swollen roots and
necrotic lesions. These symptoms indicate that yield loss is
likely to occur. However, in many cases nematode damage may
occur with little or no above ground symptomology.
Calculating corn yield loss caused by nematodes is extremely
difficult because corn nematode symptoms can be the same as
symptoms of disease and environmental pressures. Due to the
difficulty of diagnosing nematode damage, very few estimates on
corn yield loss based on nematode pressure exist. However, one
1994 estimate assessed that more than $81 million worth of corn
was lost that year in Illinois alone.
Who…or what…is in your field?
Many different species of nematodes live in the corn fields of
the United States. In fact, the majority of corn nematode
species are native to the United States and were present before
corn was even cultivated domestically. Each corn nematode
species belongs to one of three categories depending on how it
feeds on plant roots. Ectoparasitic nematodes feed from the
outside of the root while endoparasitic nematodes completely
enter the root to feed. Semi-endoparasitic nematodes only
partially enter the root to feed, while part of the nematode
remains outside the root.
Corn Nematode Species
Lesion: Lesion
nematodes are one of the most populous nematode species
found in corn fields. As an endoparasitic nematode, the
lesion nematode completely enters the root to feed and
reproduce. Corn is able to tolerate small populations of
lesion nematodes, but once the population grows, symptoms
including blackened roots, chlorosis, stunting, and nutrient
deficiency may occur.
Needle: Needle nematodes are the largest and most
destructive corn nematodes. They appear in sandy soils and
attack roots from the outside. Complications arise when
sampling for needle nematodes because they congregate in
large groups very close to the roots and do not migrate to
areas between crop rows. Needle nematodes stunt and even
kill corn seedlings early in the season, generating large
yield losses.
Root-knot: Root-knot nematodes begin to feed on the
inside of roots of corn as immature larvae. Their secretions
cause plant cells at the feeding site to enlarge and produce
galls on the roots that can be visible to the naked eye.
These galls absorb the resources of the plant and are
vulnerable to other infections. Currently, root-knot
nematodes only cause problems in corn fields in the southern
part of the United States.
Stubby-root: Stubby-root nematodes feed on the
external portion of the growing root tip. Diagnosing these
nematodes by taking soil samples is often difficult because
their short life cycles result in rapid population increases
and decreases. Stubby-root nematodes do not usually kill
corn plants, but the severe stunting they cause can reduce
yields considerably.
Lance: Lance nematodes feed on the outside of the
root, but eventually they partially or completely embed
themselves within the roots. Usually only moderate damage is
caused by infestations of this nematode.
Sting: Sting nematodes feed externally and obstruct
root elongation. These nematodes typically populate areas
that are consistently moist. Sting nematodes inject a toxic
enzyme into the roots of their host while feeding, resulting
in significant damage, yield loss and even plant death.
Dagger: Dagger nematodes are migratory ectoparasites
that feed on the outside of the roots near the tips. Dagger
nematodes can initiate severe root injury called root
devitalization by feeding on the tips of corn roots.
Ring: Ring nematodes are ectoparasitic and feed
throughout the corn root systems.
Spiral: Spiral nematodes feed on the outside of corn
roots. They may interact with other pressures and increase
stress on corn in hot and dry weather.
Stunt: More ectoparasitic nematode species are stunt
nematodes than any other type. Most corn fields have at
least a small population of stunt nematodes.
Finding the culprits
To accurately determine the presence and extent of nematode
infestations in corn, it is important to collect soil and root
samples to send to a nematode diagnostic laboratory for
analysis. Using a spade or soil probe, collect 20 soil and root
samples at least 8 inches deep in the root zone. Take the
samples randomly throughout the field but adjacent to living
plants in both the affected areas and healthy-looking areas
nearby. Be sure to include as much of the fibrous root system as
possible. The sample area should not represent more than 20
acres of corn. Experts suggest growers take multiple samples
throughout the year, but if taking only one sample is feasible,
the best time to sample is four to six weeks after planting.
Place each soil core in a plastic bag and keep it in a cool but
not freezing location, such as a refrigerator or cooler, until
you send the entire sample to the laboratory. Notify the lab
prior to shipment. Ship samples early in the week to prevent
delays over the weekend and minimize exposure to extreme
temperatures. Do not let the soil cores get too wet or dry, and
handle them as carefully as possible.
Where they live
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Putting your guard up
Corn nematode management can be very difficult. Agronomic
methods, such as tilling and crop rotation, are good starting
points in helping reduce corn nematode populations, which are
sensitive to soil disturbance. However, changing production
practices such as the increase in corn-on-corn and no-till
farming are hampering the use of these methods and helping to
escalate corn nematode populations across the Corn Belt. To help
protect corn fields against these damaging pests, Syngenta Seed
Care is developing a seed treatment nematicide and has submitted
it for EPA approval.
Want to learn more?
Click the following link to visit the Corn Nematode CEU Module
to learn more about corn nematodes and the threat they pose to
growers. After reviewing the tutorial there is a short quiz.
Certified Crop Advisers (CCA) will be eligible for one
Continuing Education Unit upon completing the quiz. A CCA must
supply his or her e-mail address and CCA number in order to
receive the quiz results.
www.farmassist.com/NematodeTutorial
©2008 Syngenta Crop Protection, Inc. P.O. Box 18300,
Greensboro, NC 27419.
Important: Always read and follow label instructions before
buying or using Syngenta products.
Syngenta Seed Care™ is a trademark of a Syngenta Group Company.
The maps included in this article are copyrighted materials and
may not be reproduced without the express, written consent of
Syngenta Crop Protection, Inc. |
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