Introduction
See Table
4-1,Symptoms in the Field
See Scouting
Calendar
See Scouting
Calendar as text
Wireworm
Identification:
The larva of this insect is the damaging stage. Wireworms are
7-35 mm long larvae that are cylindrical, copper-brown-coloured
and hardened.
See Wireworm
images
Impact and Risk Factors:
The larvae can live up to 6 years in the soil. Due to their
long life cycle, the larvae can damage several successive crops,
feeding on the roots of weeds, grasses and crop plants. They are
most active during the months of April to June and occur most
often in fields that have little disturbance. Non-uniform growth
or gaps in the stand may be due to wireworm feeding on germinating
seeds. Injured seedlings appear stunted and wilted with leaves
sometimes becoming purple or blue at the tips. The problem is
usually worse in the second year out of sod after high grass-weed
pressure, or when cereals are frequently in the rotation. They
are also generally more prevalent in sandier soils, especially
on the knolls.
Scouting Method:
Wireworms should be scouted in mid-April, prior to planting.
To scout for wireworms, a few weeks before planting, establish
two bait stations per high-action site in each field. Dig a hole
at each station, approximately 15 cm wide and 5-8 cm deep. Choose
one or two high-action sites in the field (i.e., sandy knolls,
heavy grass infestations). Bury a nylon mesh bag with 1 cup equal
parts untreated and soaked corn and wheat or freshly cut potatoes
at the bottom of the station. Mound the soil over the bait to
prevent standing water and place a flag next to it so that it
is easy to find again. Return to the stations a few days before
planting to sift through the bag contents to record the number
of larvae found per station.
Action Threshold:
One wireworm per bait station.
Management Strategies:
Use an insecticide seed treatments or in-furrow insecticide
at planting in high risk fields (i.e. fields with sandy soils
following grassy sods) or if baits indicate thresholds have been
reached. No rescue treatments are available. Control grassy weeds
in crops previous to corn.
Seedcorn Maggot
Identification:
The seedcorn maggot is a small, yellowish-white, headless,
legless larva. The maggots burrow into germinating seeds and the
below-ground parts of emerging seedlings, producing weak seedlings.
See Seedcorn
Maggot images
Impact and Risk Factors:
Damage to corn by seedcorn maggot is rare in Ontario. Seedcorn
maggot is usually a problem during cool, wet springs when germination
is delayed or seed has been planted too deep. The adult females
are attracted to moist soils that give off an odour of decaying
organic matter such as crop residues, areas where manure has been
applied or freshly tilled soil. Weeds are also attractive to females.
The maggots feed on the swollen, ungerminated seed. They can be
found in the cotyledon, embryo and hypocotyl. Slow emergence and
or reduced stand establishment can occur. Seedlings that escape
and germinate often die or lag behind.
Scouting Method:
Unlike wireworm, seedcorn maggot damage is usually found over
a generalized, large portion of the field. Look for signs of poor
stand emergence and feeding damage at the base of the newly emerging
plants. Nothing can be done to rescue a damaged field except re-planting
if necessary. High-risk factors include freshly tilled soil with
heavy crop residue, recently applied manure, recently tilled green
manure, deep planting, along with cool, backwards emergence conditions
in the forcast
Action Threshold
No threshold is available at this time.
Management Strategies
Consider insecticide seed treatments in early planted fields
where large amounts of manure or residue have been recently incorporated.
Use good quality seed that will emerge quickly and ensure seed
is not planted too deep. No rescue treatments available.
Seedcorn Beetle
Identification:
See Seedcorn
Beetle images
Impact and Risk Factors:
The beetle feeds only on the endosperm of the seed and is usually
a problem in cool, wet springs when germination is delayed. Adults
hollow out the seeds, preventing germination. Emergence of corn
up to the 3-leaf stage is the critical time when damage may occur.
Seedcorn beetles are more commonly found on heavy, moist soil,
under reduced tillage with excessive residue cover.
Scouting Method:
Adult beetles are present at the time of seed germination.
Dig up unhealthy plants or skips in emergence and examine the
seed. Examine 10 seeds or sites in five areas to determine the
extent of the problem.
Action Threshold
Replanting may be necessary if skips at proper germination
time are extensive.
Management Strategies
Planting into warmer soils will reduce chances for seed corn
beetles to cause damage.
European Chafer
Identification:
European chafer larvae are white and C- shaped with an orange-brown
head and dark posterior. This pest can be distinguished from other
white grubs by its Y-shaped pattern of anal bristles known as
"rasters," located on the underside of the last abdominal
segment of the larva.
See White
Grub images including European Chafer
Impact and Risk Factors:
In April to mid-May, overwintering larvae migrate back up close
to the soil surface and feed on plant roots. Grubs feed on the
fibrous roots, 3-5 cm from the soil surface. Roots are pruned,
causing plants to become stunted and wilt. Intense root feeding
results in poor emergence and stunted plants. Corn following soybean
crops on sandier soils near areas of turf such as lawns, golf
courses and pasture is at the highest risk.
Scouting Method:
Scout for chafers on the sandier knolls of the field. Using
a shovel, dig up approximately 1 ft of soil, about 3-4 in. deep
in each area sampled.
Action Thresholds
No thresholds are available at this time but treatment may
be necessary if there is 2 or more grubs per square foot of soil.
Management Strategies
Use insecticide seed treatment if there are more than 2 grubs
per square foot of soil. Avoid planting corn if grub population
is extreme. Cultural options include disturbing the soil by tillage
or disking, which brings the grubs to the surface where they are
exposed to the elements and natural enemies such as birds, skunks,
raccoons etc. To be effective, fall plowing must occur before
the grubs migrate below the plow depth.
Black Cutworm
Identification:
Larvae are greyish-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. Adult moths are
grey with a small black dagger marking on each forewing.
See Black
Cutworm images
Impact and Risk Factors:
Feeding occurs from early May through to mid-June. Cutworm
moths do not overwinter in Ontario but are carried in from the
south on strong southerly weather systems. Therefore injury is
more frequent in fields with green cover early in the spring before
primary tillage. Plants attacked by young larvae will have small
holes or gouges in the leaves. Larger larvae cut off the plant
at or just below ground level. Plants may suddenly wilt, because
the stem has been hollowed out. Factors that favour cutworm outbreaks
include a history of cutworm damage, presence of winter annual
weeds such as chickweed and volunteer wheat before planting, no-till
and heavy crop residue.
Scouting Method:
Start scouting for cutworm once every 5 days as soon as your
corn emerges. Pay particular attention to those areas where weeds
were heavy just before tillage and planting this spring. Look
for leaf-feeding (pinholes) by young climbing larvae as the first
sign of damage. Also look for wilting plants, foliage-feeding
or for plants being cut off at the ground. Dig around damaged
plants and search through the soil, as cutworms like to hide in
the soil during the day. Note the size of the cutworms found.
Action Thresholds
Foliar insectcide treatment should be used if more than 10%
of plants show leaf feeding. Treating at this time will give nearly
100% control. Once corn reaches the 5-leaf stage and begins to
produce roots at the base of the plant, the risk has passed.
Management Strategies
Chemical control is not effective once cutworms are nearly
mature (over 2.5 cm long). Insecticide seed treatments or Herculex
Bt corn varieties are are recommended in fields with a frequent
history of cutworm injury. Foliar insecticide treatment is most
effective when applied to the soil soon after cutworms have hatched.
Cutworms are most active in the evening, therefore insecticides
applied at this time of day are most effective. It is not necessary
to treat the entire field, only those areas showing evidence of
feeding. In no-till corn fields, it is important to have no green
vegetation that could attract the moths in early spring. Fall
burndown of volunteer crops and other weeds is recommended. Fields
should be bare for at least 2 weeks before planting.
Corn Flea Beetle
Identification:
Very tiny (1.8mm), black, shiny beetles with elongated hind
legs used for jumping when disturbed.
See Corn
Flea Beetle images
Impact and Risk Factors:
There are three to four overlapping generations per year. Only
those generations occurring from early May to late June, during
corn emergence are considered a potential problem. Only susceptible
varieties show yield loss. Long feeding scratches or window-paning
are found on the leaves, usually running parallel with the leaf
veins. Flea beetles vector Stewart's bacterial wilt which shows
up on the plant as linear lesions with wavy edges. Plants may
wilt or become stunted from this disease.
Scouting Method:
Scout early planted fields frequently (at least every 4 days).
Inspect five sets of 20 seedling plants per field to determine
the presence and density of the beetle. Sticky trap monitoring
is being developed for Ontario but is not ready for implementation
at this time.
Action Thresholds
For susceptible varieties, 6 beetles per 100 plants prior to
the 5th leaf stage warrant control. For tolerant varieties, an
average of five or more beetles per plant prior to the fourth-leaf
stage may warrant control.
Management Strategies
Mild winters favour the survival of the beetle and bacteria
over the winter. Prediction model for overwintering survival of
flea beetles is being validated for Ontario but is not ready for
implementation at this time. Early planting dates should be avoided
for parent lines susceptible to Stewart's wilt. Seed treatments
are available for flea beetle control. Additional foliar sprays
may be necessary if populations are very high.
Slugs
Identification:
Juveniles and adults are soft-bodied, legless, greyish or mottled
in appearance and have a slimy or gelatinous covering that helps
keep them from drying out. They usually range from 1-3 cm in length
but can reach up to 10 cm.
See Slug
images
Impact and Risk Factors:
Slugs prefer environments with high humidity and relatively
cool temperatures. Debris, such as crop litter or manure, provides
them with shelter from the sun. Slugs feed above or below ground
depending on the moisture level. They can feed on germinating
seeds and seedlings with no real preference for a plant part.
On larger plants, slugs feed on lower parts, eating partly or
completely through leaves, leaving ragged holes causing a skeletonized
appearance on leaves. Feeding damage can resemble that caused
by hail, and severe defoliation can result. Higher-risk fields
include those where no-till practices on corn are used for a continuous
period of time, fields with considerable crop residue and fields
following forages, especially grasses.
Scouting Method:
Scout for slugs at night or in the early morning hours, when
they are active (nocturnal). Look for stripping of leaf tissue
and/or small holes chewed in the leaves. Check under debris and
clumps of soil. A certain sign of slugs is a slimy, silver-coloured
trail on the plants or soil. Check 1.5 m of row in five locations
in the field (under clods and pieces of plant residue).
Action Threshold
No action thresholds are available. Once plants have more than
8-10 leaves, the risk of damage is greatly reduced.
Management Strategies
There are presently no economical and effective chemical methods
available for slug control. Tillage is still the best method of
control since the elimination of the crop cover exposes the slugs
to dehydration and predation by birds and mammals. Zone tillage
or row sweepers can help speed up the drying of the row area,
thus deterring slug feeding. Moving trash away from seedlings
may help reduce damage.
True Armyworm
Identification:
True armyworms, full grown, are 4 cm (1 1/2-in.) dull-green
to brown larvae that can be easily confused with other caterpillars,
including variegated cutworm and fall armyworm. Two distinguishing
features that true armyworm possess are white-bordered stripes
running laterally along the body and dark diagonal bands at the
top of each abdominal proleg. The head is yellow-brown with a
network of dark brown lines creating a pattern.
See True
Armyworm images
Impact and Risk Factors:
True armyworms overwinter in Ontario. The adult moth emerges
early spring (as early as late March) and is attracted to green
vegetation to lay her eggs on. True armyworm larvae feed at night.
In conventional-till cornfields, damage usually occurs first in
the border rows, whereas infestations may develop throughout no-till
corn following small grains or grass. True armyworm also frequently
invades corn fields from neighbouring cereal fields. Feeding begins
on the margins of leaves and eventually the plant is stripped
of leaves, with only the stalk and leaf midribs left. As long
as the growing point of the plant is not damaged, the corn plant
will be able to recover from moderate feeding.
Scouting Method:
The best time to scout for true armyworm is early evening,
just before sunset. Examine 20 plants from five locations in the
field (100 plants total). During the day, you may find the larvae
hiding in the whorl, amongst the crop debris on the soil surface
or under soil clods. Also, you may find brown frass, often mistaken
for eggs, in the whorl or on the soil near the plant. Record the
size and number of larvae.
Action Threshold
With early season feeding, insecticide may be warranted in
seedling corn if there are two or more larvae per seedling and
feeding damage exceeds 10%. For corn past the whorl stage, if
50% of the plants are showing damage and are infested with larvae
smaller than 2.5 cm (1 in.), then insecticide treatment may be
warranted.
Management Strategies
If the larvae are almost full grown (about 4 cm (1 1/2 in.)
long), there is no benefit in applying insecticide since most
of the feeding damage has already been done. Insecticides will
only be effective on larvae that are smaller than 4 cm (1 1/2
in.). Treatment may be confined to infested areas. Because grassy,
weed-infested corn is attractive to armyworm moths for egg-laying,
eliminate weeds from the corn crop and field borders. Late-season
grass control may not be a good option since this will cause the
feeding larva to migrate from the grassy weeds that are now dead
to the crop itself.
Potato Stem Borer
Identification:
Larvae are light purple to pink with distinct dark bands running
width-wise on each body segment. Larvae are approximately 4 cm
(1 1/2 in.) in length when mature.
See Potato
Stem Borer image
Impact and Risk Factors:
More severe in the eastern counties, but infestations occur
throughout the province. Small larvae initially bore into the
stalks of grassy weeds. By late May, the larvae outgrow the grass
stalks and move to nearby thicker stalk crops such as corn. Therefore
damage is usually most severe at field edges or near grassy, weedy
areas. On young plants, the larva 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 of previous year, fields following sod and conservation-till
fields.
Scouting Method:
Usually found within the stem or in soil near the base of the
plant. Look for potato stem borers along fencerows or in grassy
areas
Action Threshold
No action thresholds are available at this time.
Management Strategies
There is no effective or economic chemical control for these
insects since the borer remains inside the plant and is protected.
Good weed control this year (especially of grassy weeds) will
reduce the risk of damage next year. Fall plowing or burndown
can reduce the number of eggs to overwinter.
insect pests at knee high corn to maturity
Corn Rootworm
Identification:
There are two species of corn rootworm in Ontario. Western
corn rootworm (WCR) adults are yellow to green with three, wavy
black stripes on their wings. Northern corn rootworm (NCR) adults
are uniformly green to yellowish . Larvae are white with a brown
head and a distinct dark tail plate; they are approximately 1
cm in length.
See
Corn Rootworm images
Impact and Risk Factors:
Eggs are deposited in the soil from July until a killing frost
in the fall. The eggs overwinter and hatching begins in early
June of the following year. Adults emerge in late July where they
feed on silks and tassels. 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. Risk factors include heavier soil
(clay), high beetle populations in corn of previous season and
being the latest field planted in the previous season.
Scouting Method:
If planting corn on corn, monitor 20 plants in five different
locations in your field weekly from when adults emerge at the
end of July to the end of August.
Action Thresholds
If there is less than one beetle per corn plant on average
throughout the month of August, then no insecticide is necessary
in the following corn crop. (Note: 1 WCR = 2 NCR when counting
adults). Field corn can withstand heavy adult populations (more
than 10 adults per ear) at pollination without economic loss.
For seed corn, foliar insecticides for control of adults may be
necessary if adult populations are high enough to cause extensive
silk clipping and pollination disruption.
Management Strategies
Crop rotation is the best strategy for control. Since corn
is the primary host crop, avoid planting corn on corn. Continuous
corn fields produce up to 4 million beetles per hectare. If crop
rotation is not practical, it may be necessary to treat second-year
corn, especially on clay soils with soil insecticide, seed treatment
or rootworm Bt corn. For more information on corn rootworm biology
and transgenic corn refer to "A Grower's Handbook; Controlling
corn insect pests with Bt technology" available on the Canadian
Corn Pest Coalition's website at: www.cornpest.ca.
European Corn Borer
Identification:
Egg masses are flat, creamy white and layered over each other,
making the egg mass appear similar to fish scales. Mature larvae
are creamy white to pale grey with 2 small spots per abdominal
segment, approximately 2.5 cm in length and have a black head
. Adults are light-brown moths approximately 2 cm long with dark
wavy lines running across each forewing. Male moths are darker
and smaller than females.
See European
Corn Borer images
Distribution
There are two distinct strains in Ontario. South of a line
from Sarnia to Simcoe, there is a bivoltine strain that can undergo
multiple generations depending on the length of the season. North
of this line, there is a univoltine strain that has only one generation
per year, however, locations in southern Quebec also have two
generations per year. There is a band of overlap for these two
strains, about 50-80 km wide along this line.
Overwintering
The insect overwinters as larvae in corn stalks and other residue
left on the surface from the previous growing season. As day length
increases and average day temperatures exceed 10oC, the larvae
pupate. Pupae are found within larval feeding tunnels and require
2 weeks to develop before adults emerge.
Emergence
While emergence begins around the third week of May in the
southernmost regions of the province, moths do not usually appear
until mid-June in eastern Ontario. Once moths emerge, they fly
to nearby "action sites" or vegetative habitats such
as fencerows, ditches and hedgerows along fields.
Development
Once mated, females leave the action sites to lay eggs on the
host crop. Eggs are generally laid on the underside of leaves,
close to the midrib. Where univoltine ECB are present, larvae
develop through the season until autumn, when as fifth instars
they prepare for overwintering. Where bivoltine ECB are present,
first-generation larvae will pupate in mid-summer, emerge as adults
and complete a second generation before entering diapause in the
fall.
Impact and Risk Factors:
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 cycle, regions with a high percentage of corn (50%
or greater in region) and regions where univoltine and bivoltine
strains overlap.
Scouting Method:
In-Field Assessments
Early-season moths are attracted to taller, early-planted corn
fields while later-planted fields are more susceptible to second
generation corn borer where female moths are attracted to silking
and tasselling fields. Examine a minimum of five sets of 20 plants
per field (100 plants per field) on a 5-7 day basis basis, starting
no later than early whorl stage of corn.
For first generation scouting, look
for leaf-feeding damage. Pull out and unroll the whorl of the
damaged plants, looking for small larvae. Split the stalk of the
plants from top to ground to locate older larvae. Record the percentage
of damaged plants and number and size of larvae found.
For second generation scouting, look
for egg masses on the underside of the leaves, close to the midrib
of the plant. Concentrate scouting efforts to the three leaves
above and below the ear of the plant. Record the percentage of
plants with egg masses. Repeat scouting every 5 to 7 days until
peak moth flights have subsided in your region (approximately
1 month).
Pheromone Trapping and Adult Monitoring
Pheromone traps can be used in combination with the field scouting
to assess moth flight activity and help determine when peak egg
laying is taking place. Though there is no direct relationship
between trap counts and direct damage in the field, using trap
counts along with calculating growing degree days at base 10 will
help determine when spraying is most critical.
Several pheromone trap designs are available. Economics will determine
which design is best suited for your operation. Purchasing the
proper pheromone lures is critical as they determine the success
of your trap. For the majority of Ontario, the Iowa strain (3:97
E:Z ratio) ECB lures are effective. Small pockets in Eastern Ontario
and southern Quebec have the New York strain of ECB and will require
the New York strain type of lures (99:1 E:Z ratio). For more information
on pheromone traps, contact the OMAFRA extension entomologist
or your seed company agronomist.
Calculating growing degree days (GDD) for ECB involves the accumulation
of average daily temperatures above 10oC beginning 1 April until
the end of the growing season. ECB development is very dependant
on temperature. GDD required for ECB development in Ontario and
Quebec have been determined and are provided in the Table 4-2.
Table 4-2, ECB development
expected according to accumulated growing degree days set at base
10
| Region |
Generation |
Event |
Predicted GDD
base 10 |
|
Univoltine
|
1st Generation
|
First Catch of Moths in Traps
|
300
|
|
Peak Flight of Moths
|
650-700
|
|
Bivoltine
|
1st Generation
|
First Catch of Moths in Traps
|
150
|
|
Peak Flight of Moths
|
300-350
|
|
2nd Generation
|
First Catch of Moths in Traps
|
700
|
|
Peak Flight of Moths
|
1050
|
When reviewing growing degree day tables supplied by your company
rep or OMAFRA extension, ensure that you are following the GDD
numbers that are set at base 10 which is specific for ECB.
Economic Thresholds for non-Bt parent lines
First generation: Thresholds for
first generation are reached in seed corn when 5-10% of plants
scouted contain larvae in the whorl. Spraying should continue
on a 7 to 10 day cycle thereafter until pheromone traps and GDD
models indicate that moth flight activity has peaked and is nearly
finished.
Second generation: Thresholds for second
generation are reached in seed corn when 25% of plants scouted
contain one or more egg masses. Spraying should continue on a
7 to 10 day cycle thereafter until pheromone traps and GDD models
indicate that moth flight activity has peaked and is nearly finished.
Management Strategies
For non-Bt lines use foliar insecticides when thresholds have
been reached. Shredding debris after harvest is an effective way
to destroy borers overwintering in stalks and stubble; leave as
little stalk as possible.
If planting Bt corn, it is imperative that a refuge of at least
20% of non-Bt corn is planted along with the Bt corn to reduce
the chance of developing resistance to Bt. This refuge can be
achieved by planting strips of at least six rows wide (e.g., three
planter boxes on an 8-12 row planter) or by planting blocks of
non-Bt corn. In all cases, all Bt corn plants should be within
400 m of non-Bt corn. Do not mix Bt and non-Bt seed to achieve
refuge.
For further information on ECB or Bt corn, refer to OMAFRA
Publication 12, Sweet Corn Production Manual, and the Canadian
Corn Pest Coalition publication, A Grower's Handbook; Controlling
Corn Insect Pests with Bt Technology, available on the CCPC website
at: www.cornpest.ca.
Corn Earworm
Identification:
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. Adult moths
are buff or tan coloured. The forewing has a central brown dot
visible from the underside of the wing, and the hind wings are
pale in colour with a darker brown border.
See Corn
Earworm images
Impact and Risk Factors:
Adult moths usually arrive in Ontario in August but they may
come as early as late June. They will then lay their eggs individually
on fresh silks. 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 silking during peak population time. Unlike European
corn borer and fall armyworms, corn earworm does not leave entry
holes into the ear husk but instead concentrates its feeding at
the top third of the ear tip, leaving a messy ear tip.
Scouting Method:
Visually assess five sets of 10 plants per field and open the
ear and inspect for feeding damage or larval presence, including
the presence of ear moulds carried in by the pest. Determine the
percentage of ears infested. Corn earworm is cannibalistic and,
therefore, there is usually no more than one larva per ear of
corn.
Action Thresholds
This pest is usually only an economic pest in sweet corn but
can affect late-planted seed corn fields that are silking at time
of egg laying. One Heliothis trap per seed corn field can be used
to monitor adult activity to know when peak egg laying is taking
place. Traps need to be checked every 3 days until silks begins
to dry down.
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.
Insecticide spray should targeted at the ear and silks of the
plant. More than one application may be necessary since as silks
continue to lengthen, new egg masses will be laid on the fresh
silks. Transgenic corn gives some suppression only.
Fall Armyworm
Identification:
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 with one thicker, yellow band with
red spots running along the side, just above the legs of the larvae.
Scattered along the body are black spots called tubercles that
have spines coming from them. The fall armyworm larvae can be
distinguished from the true armyworm by a white, inverted "Y"
on the front of the head of the fall armyworm. The fall armyworm
head is dark brown to black.
See Fall
Armyworm images
Impact and Risk Factors:
Fall armyworm is an occasional pest of grass crops such as
corn and wheat. They do not overwinter here in Ontario but fly
in mid summer to early fall. 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 ragged-edged
holes; moist, reddish brown frass can be found nearby.
Scouting Method:
Examine 20 plants from five locations in your field to determine
the level of infestation. Record the size and number of larvae.
When scouting, check the backs of armyworms for parasite eggs.
These small, oval, yellowish eggs are usually located just behind
the head of the larva. These are eggs of a parasitic fly whose
maggots will kill the armyworm larvae.
Action Threshold
If 50% of the plants are infested with larvae smaller than
2.5 cm (1 in.), insecticide treatment may be warranted, but damage
is usually not economical unless infestations are high and feeding
is concentrated on the undeveloped tassels.
Management Strategies
Armyworm tend to move in large numbers from one field to another.
When this happens, it is advisable to 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. 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, eliminating 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 larva to migrate from
the grassy weeds that are now dead to the crop itself.
Corn Leaf Aphid
Identification:
These aphids are small (2mm or less), bluish green, soft-bodied
insects with black legs and short black cornicles ("tailpipes")
near the rear of the abdomen. 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.
See Corn
Leaf Aphid images
Impact and Risk Factors:
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 drought conditions, 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 also may vector
maize dwarf mosaic virus and barley yellow dwarf virus.
Scouting Method:
Examine five sets of 20 plants per field.
Action Thresholds
If 50% of all plants during late-whorl to early tassel have
400 aphids per plant, and plants are under drought stress, control
is required.
Management Strategies
Chemical control is warranted only if aphid populations are
gumming up the tassels, significantly reducing pollination. There
are several biological control agents that exist and are quite
effective. These include ladybird beetle adults and larvae, lacewing
adults and larvae, and a few parasitic wasps.
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