CORN INSECTS

AND PESTS
DESCRIPTION
AND ITS LIFE
CYCLE
RAMIL C.
SUBINGSUBING
TOT CORN FACILITATOR
Black Cutworm (Agrotis ipsilon)
Description:
Larvae are grayish-black with a paler underside
and no distinct markings on their bodies. Mature larvae
are about 3.5 cm (1 1/4 in.) long and hide in the soil
during the day. They can be found near freshly cut
plants, under soil clumps or along a poorly closed seed
furrow. Adult moths are grey with a small black dagger
marking on each forewing.
Damage:

Plants attacked by young larvae

will have small holes or gouges in the
leaves. Plants may suddenly wilt,
because the stem has been hollowed
out or fed on underground. Larger
larvae cut off the plant at or just below
ground level. Factors that favor
cutworm outbreaks include a history of
cutworm damage, presence of winter
annual weeds such as chickweed and
Management Strategies:

* Using seed treatments specifically for black cutworm

control is not recommended, since cutworm is a sporadic
pest. For fields with a frequent history of cutworm injury,
consider planting Bt corn hybrids containing Cry1F and/or
using an insecticide seed treatment at planting. These
products are most effective on younger larvae.

* Foliar insecticide treatment is most effective when

applied to the soil soon after cutworms have hatched.
Cutworms are most active in the evening, so insecticides
applied at night/evening are more effective. Foliar
insecticide application to mature larvae (larger than 2.5
cm or 1 in.) is not recommended since most of the
damage has occurred and control may be inadequate.

* It is not necessary to treat the entire field, only those

Corn Flea Beetle (Chaetocnema
pulicaria)
Description:
Very tiny (1.8 mm), black, shiny beetles with
elongated hind legs, which are used for jumping when
disturbed.
Damage:
Planting seasons following mild winters
experience higher beetle activity. Only
susceptible varieties and seed corn inbreds
show yield loss. Long feeding scratches or
window-paning are found on the leaves,
usually running parallel with the leaf veins.

Flea beetles are vectors of Stewarts'

bacterial wilt, which over-winters in the gut
of the insect. Symptoms of Stewarts' wilt
include linear lesions on the leaves with
wavy edges. Plants may wilt or become
stunted from this disease.
Management Strategies:
Models help predict the risk of high adult
activity each year based on winter temperatures
and adult survival.

* Use insecticide seed treatments on susceptible

hybrids and inbreds, and for those fields with a
history of flea beetle activity.

* Avoid early planting dates for varieties

susceptible to Stewart's wilt. Plant fields with a
history of Stewart's wilt to resistant hybrids.

* Additional foliar sprays may be necessary for seed

corn and susceptible varieties if populations are
very high. It is not economical to spray corn with
insecticides to protect against the flea beetles
Potato Stem Borer (Hydraecia
micacea)
Description:
Larvae are light purple to pink, and
approximately 4 cm (1 1/2 in.) in length when
mature. Adults are brown moths that are active
during August and September.
Life History:

This pest is more severe in the eastern

counties, but infestations occur throughout the
province. There is one generation per year.
Eggs are laid in two or three parallel rows
under the leaf sheath.
These hatch in late April, and the small
larvae initially bore into the stalks of grass plants.
By late May, the larvae outgrow the grass
stalks and move to nearby thicker stalk crops
such as corn. These larvae continue to feed until
late June, pupate and emerge as adults in late
July.
Damage:
Larvae are the only damaging stage.
Damage is usually most severe at field edges or
near grassy, weedy areas. Larvae feed on plants
in late May through early June. On young plants,
the larvae will burrow into the base of the plant,
below the soil line. Plants may be cut at the base,
similar to cutworm injury. At the three or more
leaf stage, they feed inside the whorl at the base
of the corn plant, causing the upper one or two
leaves to wilt, while the lower part of the plant
remains healthy. Fields at higher risks include
grassy or weed-infested fields the previous year;
fields following sod and conservation-till fields.
Management Strategies:
* There is no effective or economic chemical
control for this insect, since the borer remains
inside the plant where it is protected.

* Good weed control, especially of grassy weeds,

is effective in reducing the risk of damage next
year.

* Fall plowing or burn down can reduce the

number of over-wintering eggs. Parasitic wasps
generally keep this pest below economically
damaging levels.
Europeian Corn Borer (Ostrinia nubilalis)

Description:
European corn borer (ECB) egg masses are
flat, creamy white and layered over each other,
making the egg mass appear similar to fish
scales.
Damage:
Early-season larvae feed on leaves, creating
small pinholes and eventually migrate into the
whorl of the plant and attack the enclosed tassel.
Later-season larvae feed briefly on the leaves,
bore into the midrib of the leaf and then migrate
into the stalk of the plant and husk of the ear.
Larvae may also feed directly on the developing
kernels. Stalk lodging and ear droppage may
occur as a result of significant infestations. This
pest can carry both stalk rots and ear rots into
the plant. High-risk factors include no-till fields
with high residue, those with frequent corn crops
in the rotation, regions with a high percentage of
corn (50% or greater in region) and regions where
Management Strategies for Non-Bt Corn
Hybrids:

* Insecticides have generally not provided economic

control of ECB in field corn.

* When ECB Bt corn hybrids cannot be used, select non-

Bt corn hybrids with resistance or tolerance to ECB
feeding that have good agronomics.

* Shredding debris after harvest is an effective way to

destroy borers over-wintering in stalks and stubble. Leave
as little stalk as possible.

* Immature stages of ECB are attacked by natural

enemies, which contribute to reducing population
densities. Predators such as lady beetles and minute
pirate bugs feed on the eggs and young larvae. Parasitic
Management Strategies for ECB Bt Corn Hybrids:

• If ECB is a moderate-to-high risk in your

region, consider planting transgenic Bt corn
hybrids that control ECB. Use Bt hybrids
that express the Bt toxin in the ear as well
as the stalk to help avoid stalk and ear rot.

* If ECB Bt corn is planned, the Canadian

Food Inspection Agency requires that insect
resistance management strategies be
followed. This requirement is endorsed by
the Canadian Corn Pest Coalition.
Corn Rootworm (Diabrotica virgifera and Diabrotica
barberi)
Description:
There are two species of corn rootworm
(CRW) in Ontario. Western corn rootworm (WCR)
adults are yellow to green with three black stripes
on their wings
Damage:

Both adults and larvae feed on corn. Larvae

feed on and within the roots from mid-June to
mid-July, interfering with nutrient and water
uptake, causing stress to the plant. Larger larvae
feed on the brace roots, reducing the stability of
the plant, causing it to lodge or gooseneck. Adults
feed on pollen and clip the silks, interfering with
pollination. If tassels and ears have not emerged,
they will feed on the leaves, stripping tissue on
the underside of leaves between the veins,
leaving "window panes." Risk factors include
continuous corn fields, fields with high beetle
populations in corn from previous seasons or
Management Strategies:
• Crop rotation is the best strategy and is superior to
insecticides for reducing rootworm populations. Since corn
is the primary host crop, avoid planting corn on corn.
Continuous corn fields produce up to 4 million beetles per
hectare.

• Although rootworm insecticides can protect the crop

from damage, on average they reduce beetle emergence
by only 25%.

* If crop rotation is not practical, it may be necessary to

treat fields of continuous corn with high rate insecticide
seed treatment, soil-applied insecticide or to plant
transgenic CRW Bt hybrids.

* If extensive goose-necking occurs or monitoring for

adults in August shows significant populations, and corn is
targeted for the field next year, use of a control strategy
Western Bean Cutworm (Striacosta
albicosta)
corn, dry edible beans
Description:
Western bean cutworm (WBC) larvae are tan
to pink in colour and do not have warts or spots
(tubercles) on them, unlike European corn borer.
The only distinguishing marking WBC larvae have
is on their pronotum, the shield-like structure just
behind the head of the larvae. The WBC's
pronotum has two broad dark brown stripes. Adult
moths are easy to identify from other corn pests.
Each wing of the moth has a white band running
along the edge or margin of the wing and has a
spot or "moon" and boomerang-like mark on it.
Damage in Corn:
Young larvae feed on the tassels and silks
until they are large enough to tunnel into the ear
and feed extensively on the kernels. In whorl-
stage corn, larvae will feed on the developing
pollen. Entry holes can sometimes be seen on the
outside of the husk though they can also enter
through the silk channels. Unlike corn earworm,
western bean cutworms are not cannibals and
therefore multiple larvae can feed on the same
ear. Additional impact to quality can be expected
from ear rots and secondary pests that may come
in and feed on the damaged ears.
Management Strategies for Corn :
* Transgenic Bt corn hybrids containing Cry1F protein
provide some protection from WBC.

* Foliar insecticide timing is critical. Once the larvae

enter the corn ear, or bean pod, insecticides are no longer
effective.

* Timing of application must coincide with egg hatch

when young larvae are feeding.

* Deep tillage can help disturb and kill larvae over-

wintering in soil chambers.

* Heavy rain can reduce young larvae survival.

* Several natural enemies feed on egg masses and young

Corn Earworm (Helicoverpa zea)
Description:
Corn earworm larvae vary greatly in colour from
light green to yellow. The full-grown larvae are 4 cm (1
1/2 in.) long with prominent stripes running the length of
their bodies.
Damage:
Larvae may feed on leaves and tassels but
mainly are found feeding on silks and developing
kernels. Larvae damage tassels, causing poor
pollination, and consume silks, affecting ear
development. Fields at risk are those planted late
that will be freshly silk during peak larvae
population time.

Unlike European corn borer, western bean

cutworm and fall armyworm, corn earworm does
not leave entry holes into the ear husk as it
enters directly via the silk channels. Feeding is
concentrated at the top third of the ear tip.
Management Strategies:
* Earlier-planted corn may have a chance to escape the
peak infestations of corn earworm if they silk early
enough.

* Insecticides have generally not provided economic

control of corn earworm in field corn. There may be some
value in treating seed corn to maintain kernel quality.

* Several natural enemies exist in the field, including

trichogramma wasps, lady beetles, lacewings and
parasitic flies, that help to keep pest populations in check.

* Some transgenic Bt hybrids provide suppression of corn

earworm but should not be used for the sole purpose of
controlling a sporadic pest such as corn earworm.
Fall Armyworm (Spodoptera
frugiperda)
corn, winter cereals
Description:

Full-grown fall armyworms are 4

cm (1 1/2 in.) long, varying in colour
from light tan or green to near-black.
Three white, thin strips run down the
back. One thicker, yellow band with
red spots runs along the side, just
above the legs of the larvae.
Damage:
Fall armyworm is an occasional pest of grass
crops such as corn and wheat. The larvae feed on
the whorl leaves and ears predominately from
late July to September. Fall armyworm feeding
occurs in the daytime, unlike true armyworm
feeding, which occurs at night. Initial leaf feeding
appears as tiny holes similar to ECB feeding but
as the larvae grow, holes become very large, with
ragged edges. Moist, reddish-brown grass can be
found nearby.

Damage to the ear is similar to that of corn

earworm. However, the fall armyworm entry hole
can easily be seen coming from the side of the
Management Strategies in Corn:
* Bt corn hybrids containing Cry1F protein provide some
protection against fall armyworm.

* Armyworm tend to move in large numbers from one field to

another. When this happens, spray the border of the invaded
field. Chemical control is not effective on larvae larger
than 2.5 cm (1 in.) or on those concentrated in the ear.

• Parasites and other beneficial organisms usually keep

armyworms from reaching damaging levels. Avoid treating with
insecticides when large numbers of parasitized larvae are
present.

* Late-planted corn is most susceptible to leaf and whorl

feeding. Grassy areas in and along the field borders are
attractive to the egg-laying moths. Therefore, controlling
grasses and weeds from the corn field is recommended. Late-
season grass control may not be a good option since this will
cause the feeding larvae to migrate from the grassy weeds that
Corn Leaf Aphid (Rhopalosiphum
maidis)
Description:
These aphids are small (2 mm or less),
bluish-green, soft-bodied insects with black
legs and short black cornicles ("tailpipes")
near the rear of the abdomen Plate 81.
They have piercing and sucking mouthparts
and feed on the juices (nutrients) of young
plant tissue (tassel and whorl). They
secrete a sticky substance referred to as
"honeydew," which can become coated
with a blotchy, sooty mould.
Damage:
The degree of feeding injury depends
on the size of the population. Nymphs and
adults feed primarily on the whorls of the
plant, removing nutrients and water.
Symptoms include yellowing, wilting and
curling of the leaves. During dry periods
when the plants are stressed, symptoms
may be amplified. As densities increase,
leaf surfaces and tassels often become
black and sooty as mould begins to grow
on the honeydew. Tassels may become
gummy, causing poor pollination. They are
Management Strategies:
* Chemical control is warranted only if the
natural enemies and parasites of the corn
leaf aphids are not present and aphid
densities are above threshold. There are
several natural enemies that exist and are
quite effective at controlling corn leaf
aphids. These include lady beetle adults
and larvae, lacewing adults and larvae, and
a few parasitic wasps.

* Chemical control will kill natural enemies

and may lead to a resurgence of the aphid
“It's not the monkey on
top that make a tree fall
but it's the work and
effort of numerous small