Corn Production Guide (continued)
A-1130, May 1997
Insect Management in Corn
Corn Leaf Aphid
The corn leaf aphid is a bluish green color with black legs,
cornicles, and antennae. The populations can build up very
rapidly on corn, especially on the tassles. Infestations on corn
are seldom economically important, except in late seeded crops or
crops growing under drought stress.
Threshold
The critical period for injury by corn leaf aphid is during
tassel emergence through pollination. Treatment is suggested only
when 50% of the corn plants have 100+ aphids per plant during
tassel emergence and plants are drought stressed.
Natural controls
Lady beetles, Aphid lions, Syrphid fly, and parasitic wasps
play a major role in reducing aphid populations. When natural
enemies are present in large numbers, and the crop is well
developed, farmers are discouraged from spraying fields.
Dosage in LB AI Product Rate
Insecticide per Acre per Acre Remarks
-------------------------------------------------------------------------
Dimethoate 0.33 to 0.5 0.66 to 1 pt Do not harvest, feed, or
(Cygon 400, graze within 14 days of last
application. Do not make
more than three applications
per season. Do not apply to
corn during the pollen-shed
period.
-------------------------------------------------------------------------
Di-Syston* 0.5 to 1 8 to 16 fl oz Aerial application only. Do
not apply within 28 days of
corn harvest.
-------------------------------------------------------------------------
Ethyl 0.25 8 fl oz Aerial application only. Do
parathion 4E* not apply within 12 days of
corn harvest. Do not enter
treated fields within 3 days
after application. Fields
must be posted.
-------------------------------------------------------------------------
Lorsban 4E 0.5 to 1 1 to 2 pts Do not apply within 14 days
of corn silage harvest nor
35 days of corn grain
harvest. Apply by air,
ground or chemigation
(treatment through
irrigation systems) in
sufficient water for
adequate coverage.
-------------------------------------------------------------------------
Lannate LV* 0.225 to 0.45 0.75 to 1.5 pts Do not harvest within 21
days or feed treated forage
within 3 days of
application. Field re-entry
interval is 2 days.
-------------------------------------------------------------------------
Methyl 0.25 8 fl oz Aerial application only. Do
parathion 4 EC* not use within 12 days of
corn harvest. Do not enter
treated fields within 48
hours after application.
Fields must be posted. Do
not apply during pollen
shed.
-------------------------------------------------------------------------
Penncap-M* 0.5 to 0.75 2 to 3 pts Do not apply within 12 days
of harvest or grazing. To
avoid injury to bees, do
not apply during pollen shed
if bees are visiting the
areas to be treated during
foraging hours. Do not enter
treated fields within 48
hours after application.
Fields must be posted.
-------------------------------------------------------------------------
Armyworms
Armyworm outbreaks in North Dakota can occur when large
migrations of moths from southern states occur in late spring and
early summer. Moths prefer to lay eggs in moist, shady areas
where small grains or grasses have lodged or been damaged by hail
or wind. Armyworms feed at night and hide under vegetation or in
loose soil during the day. To scout for armyworms in grains, part
the plants and inspect the soil for fecal pellets. If pellets or
feeding damage are found, look for larvae under plant trash, soil
clods or in soil cracks.
Threshold
Treat when 25 to 30% of the plants have two or more worms or
75% of the plants have one worm.
Migrating armyworms
Treat a couple of swaths ahead of the infestation in the
direction of movement to form a barrier strip.
Dosage in LB Product Rate
Insecticide AI per Acre per Acre Remarks
-------------------------------------------------------------------------
permethrin 0.1 to 0.2 Ambush: Apply prior to brown silk.
(Ambush* 6.4 to 12.8 fl oz Apply a minimum of 1 gallon
and Pounce*) Pounce: of finished spray per acre
4 to 8 fl oz by air and 10 gallons per
acre by ground equipment.
Do not apply within 30 days
of harvest.
-------------------------------------------------------------------------
Asana XL* 0.03 to 0.05 5.8 to 9.6 fl oz Do not apply within 21 days
of harvest.
-------------------------------------------------------------------------
Carbaryl 1 to 2 rate varies Do not apply within 0 days
(Sevin) by formulation of harvest.
-------------------------------------------------------------------------
Ethyl 0.375 12 fl oz Aerial application only. Do
parathion 4E* not apply within 12 days of
harvest. Do not enter
treated fields within 3
days after application.
Fields must be posted.
-------------------------------------------------------------------------
Lannate LV* 0.225 to 0.45 0.75 to 1.5 pts Do not harvest within 21
days or feed treated forage
within 3 days of
application. Field re-entry
interval is 2 days.
-------------------------------------------------------------------------
Lorsban 4E 0.5 to 1 1 to 2 pts Do not apply within 35 days
of harvest. Do not apply
more than 15 pints by post-
emergence application/
season. Do not allow
livestock to graze in
treated areas within 14 days
or feed treated corn silage,
fodder or grain to meat or
dairy animals within 35 days
after treatment.
-------------------------------------------------------------------------
Methyl 0.25 8 fl oz Aerial application only. Do
parathion 4EC* not apply within 12 days of
corn harvest. Do not enter
treated fields within 48
hours or application. Fields
must be posted.
-------------------------------------------------------------------------
Penncap-M* 0.5 to 0.75 2 to 3 pts Do not apply within 12 days
of harvest. Do not enter
treated fields within 48
hours after application.
Fields must be posted.
-------------------------------------------------------------------------
Warrior* 0.02 to 0.03 2.56 to 3.84 Do not apply within 21 days
fl oz of harvest. When applying
by air, apply in a minimum
of 2 gallons of water per
acre. For control of first
and second instar only.
-------------------------------------------------------------------------
Cutworms
Management in corn
Some criteria that may help predict cutworm problems are: 1)
field history of cutworm damage; 2) surface crop residue from
reduced or minimum tillage; 3) bottom land or low spots in field;
4) fair to poor drainage; 5) near shelterbelts with grassy ground
cover. Eggs of the important cutworms are laid during late summer
in North Dakota. Soil moisture at this time is important for
survival. Growers should be cautious when planting corn following
pasture, alfalfa, or clover sites where survival may be greater.
Threshold
Begin scouting for cutworms when corn is up to a stand and
continue until mid June. Treat when 3 to 6% of the plants are cut
and small larvae (<3/4 inch) are present. Application rate of
15 to 20 gallons of water per acre by ground application is
suggested.
Dosage in LB AI Product Rate
Insecticide per Acre per Acre Remarks
-------------------------------------------------------------------------
permethrin 0.1 to 0.2 Ambush: Apply prior to brown silk.
(Ambush* 6.4 to 12.8 Apply a minimum of 1 gallon
and Pounce*) fl oz of finished spray per acre
Pounce: by air and 10 gallons per
4 to 8 fl oz acre by ground equipment.
Do not apply within 30 days
of harvest.
-------------------------------------------------------------------------
Asana XL* 0.03 to 0.05 5.8 to 9.6 Do not apply within 21 days
fl oz of harvest.
-------------------------------------------------------------------------
Carbaryl 2 to 3 rate varies Spray in 12-inch band over
(Sevin) by formulation the row. No limitationon
on age.
-------------------------------------------------------------------------
Sevin 5% bait 1 to 2 20 to 40 lbs Broadcast treatment. No
limitation on forage. Do not
incorporate bait.
-------------------------------------------------------------------------
Lorsban 4E 0.5 to 1.0 1 to 2 pts Do not apply more than 15
pints by postemergence
application per season.
Postemergence broadcast
treatments should be with
sufficient water to provide
good coverage. If soil is
dry, rotary hoeing can
improve control if no
rainfall occurs. Do not
allow livestock to graze in
treated areas within 14 days
or feed corn silage, fodder
or grain to meat or dairy
animals within 35 days after
treatment.
-------------------------------------------------------------------------
Warrior* 0.015 to 0.025 1.92 to 3.2 In corn, may be applied
fl oz before, during, or after
planting for cutworm
control. Do not apply within
21 days of harvest. When
applying by air, apply in a
minimum of 2 gallons of
water per acre.
-------------------------------------------------------------------------
Corn Rootworm Larvae
Rootworm larvae injure the root system of the corn plant.
Yield potential may be reduced and/or lodging of plants may
occur. Annual crop rotation from corn should prevent serious
damage and losses. Early planting of corn allows for better root
development prior to the late June hatch of rootworm eggs.
Threshold
The decision to rotate from corn or to use an insecticide may
be based on field scouting for adult beetles during a three week
period after pollination. Record the number of corn rootworm
beetles on the foliage and silk of 100 plants. When the adult
population averages one beetle per plant in continuous corn or
0.5 beetles per plant in first year corn fields, the potential
for larval root damage the next summer is sufficient to rotate
from corn or to apply an insecticide.
Dosage in LB AI Product Rate
Insecticide per Acre per Acre Remarks
-------------------------------------------------------------------------
Aztec 2.1 G* varies by 6.7 oz/1,000 ft May be applied at planting
row spacing of row as band, T-band, or in
furrow treatment. Cover or
incorporate spills
(including end row
spillage). Do not use on
other crops grown for food
or forage.
-------------------------------------------------------------------------
Counter 15 G* varies by 8 oz/1,000 ft May be applied in a 7-inch
row spacing of row band at planting or in the
seed furrow behind the
planter shoe. Do not exceed
8.7 lbs of product per acre.
Do not apply Accent or
Beacon herbicide to corn
treated with Counter 15 G.
-------------------------------------------------------------------------
Dyfonate varies by 8 oz/1,000 ft Application at planting:
15 G row spacing of row Incorporate into the top 0.5
to 1 inch of soil by
dragging a short length of
chain behind the press
wheels. Application at
cultivation: Cover the
treated band with 2 to 3
inches of soil by making
application immediately
ahead of disc tillers or
cultivation equipment. Do
not apply within 30 days of
harvest. Do not exceed
27 lbs of product per acre.
-------------------------------------------------------------------------
Force 1.5 G* varies by 1.5G: 8 to 10 Apply in a 7-inch band or
and 3 G* row spacing oz/1,000 ft; in-furrow behind the planter
3G: 4 to 5 shoe in front of the press
oz/1,000 ft wheel. Do not rotate to
of row another crop within 30 days
after application.
-------------------------------------------------------------------------
Fortress varies by 2.5 G: Apply as a T-band or
2.5 G* row spacing 6 oz/1,000 ft in-furrow at planting. Do
and 5 G* of row 5 G: not apply as a surface band
3 oz/1,000 ft behind the press wheel.
of row Granules exposed on the soil
surface must be
incorporated. Crop
rotational intervals:
corn - anytime;
other crops - 30 days.
-------------------------------------------------------------------------
Lorsban 15 G varies by 8 oz/1,000 ft Apply in a T-band or
row spacing of row in-furrow in front of press
wheels at planting time or
at time of cultivation. Not
more than 1 application per
season. Incorporate into
top 0.5 to 1 inch of soil
using chains or tines behind
press wheel.
-------------------------------------------------------------------------
Phorate 20 G* varies by 6 oz /1,000 ft Apply in a 7-inch band over
row spacing of row the row directly behind the
planter shoe in front of the
press wheel or at the time
of cultivation in a band at
base of plants and cover
with soil. Do not apply in
direct contact with soil.
-------------------------------------------------------------------------
Thimet 20 G* varies by 6 oz /1,000 ft Place granules in a 7-inch
row spacing of row (minimum band over the row behind the
30 inch row press wheel and lightly
spacing) incorporate. Do not use
in-furrow application. Do
not use more than 6.7 lbs of
product per acre.
-------------------------------------------------------------------------
Corn Rootworm Adults
Rootworm beetles feed on the leaves, silk and pollen of corn.
Occasionally, the beetles congregate and feed on silks during
early pollen shed. If silks are chewed back to the tips of ears
(less than 1/2 inch of silks protruding) during the period of
maximum pollen shed, poor pollination and grain set can occur.
Adult injury very seldom occurs in North Dakota.
Threshold
When an average of five or more beetles per silk mass are
found during the first week of pollen shed, control may be
necessary. Another management threshold uses silk clipping. When
silk clipping is occurring on 25 to 50% of the plants during
pollen shed, control would be justified.
Egg laying suppression programs
Compel and Slam are two new products used for egg laying
suppression. Both products contain Curcurbitacin, a rootworm
feeding stimulant. The use of these "bait" products is
still in the experimental and promotional phase. Research trials
in Midwest states have not provided consistent results at this
point.
Dosage in LB AI Product Rate
Insecticide per Acre per Acre Remarks
-------------------------------------------------------------------------
Asana XL* 0.03 to 0.05 5.8 to 9.6 Do not apply within 21 days
fl oz of harvest.
-------------------------------------------------------------------------
Carbaryl 1 to 2 rate varies No preharvest interval.
(Sevin) by formulation
-------------------------------------------------------------------------
Lorsban 4E 0.5 to 1 1 to 2 pts Do not apply within 35 days
of harvest. Apply by air,
ground or chemigation.
-------------------------------------------------------------------------
Malathion 8EC 1 to 1.25 1 to 1.25 pts Do not apply within 5 days
of harvest.
-------------------------------------------------------------------------
Malathion (ULV) 0.3 4 oz Do not apply within 5 days
of harvest.
-------------------------------------------------------------------------
Penncap-M* 0.25 to 0.5 1 to 2 pts Do not harvest, cut for
forage, or graze within 12
days of application. See bee
precautions on label. Do not
enter treated fields within
48 hours after application.
Fields must be posted.
-------------------------------------------------------------------------
Warrior* 0.02 to 0.03 2.56 to 3.84 Do not apply within 21 days
fl oz of harvest. When applying by
air, apply in a minimum of 2
gallons of water per acre.
-------------------------------------------------------------------------
European Corn Borer
Managing corn borer in North Dakota is a challenge due to the
lengthy emergence interval of the moths from overwintering. In
North Dakota, borers have the potential for one or two
generations during the season. The two generation borers are
present in the southeastern quarter and of the state. They begin
emerging in early June and represent the first flush of larval
feeding. The single generation borer is present throughout North
Dakota, emerging from mid June and beyond. The challenge of the
crop manager is to distinguish when egg laying and larval
populations can be tolerated or they need to be controlled. Corn
should be monitored weekly for at least five weeks
once plants exceed an extended leaf height of 17 inches. At this
point, corn borer larvae will be able to survive on the plant.
Inspect plants for the presence of egg masses, whorl feeding, and
active larvae. Observing moth activity around field margins or
within the field may alert you to developing infestations. Recent
corn borer infestations in North Dakota developed in mid to late
July and August as a result of the late emergence of the numerous
single generation type borers. In other years, the two generation
borers emerging first may contribute more to significant
infestations.
Field scouting for corn borers
Whorl stage corn — Pull the whorls from 10
plants at five locations across the field. Select whorls at
random, avoiding damaged plants. Unwrap the whorl leaves; count
and record the number of live larvae found.
Tassel stage or older corn — Examine the
underside of the middle 7 leaves (3 leaves above and 3 leaves
below the ear leaf) on 20 plants from 5 locations in the field.
Multiply the number of egg masses found by 1.1 (correction factor
for eggs on other leaves). Complete worksheet to determine the
need for treatment.
Worksheet for whorl stage corn — you fill in the blanks
1. ____% of plants infested x _____ Avg no. borers/plant =
_____ Borers per plant
2. _____ borers per plant x _____ percent yield loss per borer* =
_____ percent yield loss
3. _____ percent yield loss x _____ expected yield (bu. per acre)
= _____ bushels / acre loss
4. _____ bushel loss per acre x _____ price per bushel = $_____
loss per acre
5. _____ loss per acre x _____ percent control** = $_____
preventable loss/a
6. _____ preventable loss/acre - _____ cost of control per acre =
$_____ profit (loss)/acre
* 5% for corn in the early whorl stage; 4% for late whorl; 6%
for pretassel
** 80% for granules; 70% for sprays.
Worksheet for tassel stage or older corn — you fill in
the blanks
1. _____ egg masses per plant* x 4.5 borers per egg mass =
_____ borers per plant
2. _____ borers per plant x _____ percent yield loss per borer**
= _____ % yield loss
3. _____ percent yield loss x _____ expected yield (bu. per acre)
= _____ bushels / acre loss
4. _____ bushel loss per acre x _____ price per bushel = $_____
loss per acre
5. _____ loss per acre x 80 percent control = $_____
preventable loss/a
6. _____ preventable loss/acre - _____ cost of
control per acre = $_____ profit (loss) / acre
* Cumulative counts taken five to seven days later can be
added here
** Use 0.04 for pollen-shedding corn, 0.03 if kernels are
initiated
Dosage in LB Product Rate
Insecticide AI per acre per Acre Remarks
-------------------------------------------------------------------------
permethrin 0.1 to 0.2 Ambush: 6.4 Apply prior to brown silk.
(Ambush* to 12.8 fl oz Apply a minimum of 1 gallon
and Pounce*) Pounce: of finished spray per acre
4 to 8 fl oz by air and 10 gallons per
acre by ground equipment. Do
not apply within 30 days of
harvest.
-------------------------------------------------------------------------
Asana XL* 0.04 to 0.05 7.8 to 9.6 Do not apply within 21 days
fl oz of harvest.
-------------------------------------------------------------------------
Carbaryl 1.5 to 2 rate varies No preharvest interval.
(Sevin) by formulation
-------------------------------------------------------------------------
Bacillus see specific labels No preharvest interval.
thuringiensis for rate recommendations Non-toxic to man or
wildlife. Application to
newly hatched larvae
critical for best
performance. Products
currently labeled are:
Agree�, Biobit�, Condor G�,
Dipel�, Javelin�, M-Peril�,
MVP�.
-------------------------------------------------------------------------
Dyfonate rate varies Band: 4 to 8 Apply granules over the
15 G by application oz/1,000 whorl. Do not apply within
ft of row 30 days of harvest nor feed
Broadcast: or graze livestock within
5 to 6.75 lbs 30 days of treatment.
-------------------------------------------------------------------------
Furadan 4F* 0.75 to 1 1.5 to 2 pts Do not make more than two
applications per season at
this rate. Do not apply
within 30 days of harvest.
Do not apply to seed corn
less than 14 days prior to
detasseling or rogueing. If
prolonged intimate contact
will result, do not re-enter
treated fields within 14
days of application without
wearing proper protective
clothing.
-------------------------------------------------------------------------
Lorsban 4E 0.75 to 1 1.5 to 2 pts Apply in at least 2 to 5
gallons water per acre by
0.5 to 1 1 to 2 pts air. For ground application
(chemigation) to control 2nd generation
use +10 GPA if directed
spray or +15 GPA if
broadcast. For best results
when chemigating, add 2 pts/
acre non-emulsifiable crop
oil. May be applied by
center pivot irrigation
according to label
restrictions. Do not allow
livestock to graze in
treated areas within 14 days
or feed treated corn silage,
fodder or grain to meat or
dairy animals within 35 days
after treatment.
-------------------------------------------------------------------------
Lorsban 0.66 to 1 3.5 to 8 oz/ Restrictions same as above.
15 G 1,000 ft of row May be broadcast aerially or
directed into banded with suitable ground
the whorl application equipment prior
to tassel emergence. Use
high rate (6.5 lb product
per acre) when applying
broadcast.
-------------------------------------------------------------------------
Penncap-M* 0.5 to 1 2 to 4 pts Apply when first eggs begin
to hatch. May be applied by
center pivot irrigation
according to label
restrictions. Observe label
precautions for bees. Do not
harvest, cut for forage, or
graze within 12 days of
application. Do not enter
treated fields within 48
hours after application.
Fields must be posted.
-------------------------------------------------------------------------
Pounce 0.1 to 0.2 6.7 to 13.3 lbs Apply prior to brown silk
1.5 G* stage.
-------------------------------------------------------------------------
Warrior* 0.02 to 0.03 2.56 to 3.84 Do not apply within 21 days
fl oz of harvest. When applying by
air, apply in a minimum of
2 gallons of water per acre.
-------------------------------------------------------------------------
Grasshoppers
In the northern plains, grasshopper egg hatch normally begins
in late April to early May. Peak hatch occurs about mid June.
Heavy infestations typically occur in areas of low rainfall or
during drought years. Outbreaks are usually preceded by several
years of hot, dry summers and warm falls. Cool, wet weather
increases disease occurrence and delays development of
grasshoppers, reducing the overall population.
Cultural Control Methods
Early seeding allows for early establishment and
vigorous growth of plants.
Crop rotation avoid planting in areas of high egg
deposits. Fields with late maturing crops or green plant
cover attract adults which then lay eggs.
Tillage Summer fallow will act as a trap crop,
attracting females for egg laying. Spring tillage of these
sites will reduce successful emergence of nymphs.
Grasshopper Thresholds
Infestation Ratings
Nymphs (young hoppers) Adults
----------------------- ----------------
Rating Margin Field Margin Field
------------------------------------------------------
- - - - - - per square yard - - - - - -
Light 25-35 15-23 10-20 3-7
Threatening 50-75 30-45 21-40 8-14
Severe 100-150 60-90 41-80 15-28
Very Severe 200+ 120 80+ 28+
------------------------------------------------------
Dosage in LB Product Rate
Insecticide AI per Acre per Acre Remarks
-------------------------------------------------------------------------
Asana* 0.03 to 0.05 5.8 to 9.6 Do not apply within 21 days
fl oz of harvest.
-------------------------------------------------------------------------
Dimethoate 0.5 1 pt Do not apply within 14 days
(Cygon 400, of harvest, feeding, or
Dimethoate 400) grazing. Do not make more
than three applications per
season. Do not apply during
pollen-shed period.
-------------------------------------------------------------------------
Carbaryl 0.5 to 1.5 Rate varies Do not apply within 21 days
(Sevin) by formulation of grain harvest. Do not
make more than 2
applications after the boot
stage. No limitations on
forage. The lower rate
(0.5 lb) is suggested for
nymphs on small plants or
sparse vegetation. The
higher rate is suggested for
mature grasshoppers or when
material is applied to crops
requiring greater coverage.
-------------------------------------------------------------------------
Ethyl 0.375 12 oz Aerial application. Do not
parathion 4E* apply within 12 days of corn
harvest. Do not enter
treated fields within 3 days
after application. Fields
must be posted.
-------------------------------------------------------------------------
Furadan 4F* 0.125 to 0.25 4 to 8 fl oz Do not forage cut or harvest
within 30 days of last
application. Use a minimum
of 10 gal of finished spray/
acre with ground equipment
and 2 gal/acre with aerial
equipment.
-------------------------------------------------------------------------
Lorsban 4E 0.25 to 0.5 0.5 to 1 pt Do not allow livestock to
graze in treated areas
within 14 days nor feed
treated corn silage, fodder
or grain to meat or dairy
animals within 35 days after
treatment.
-------------------------------------------------------------------------
Malathion 8 EC 1 to 1.25 1 to 1.25 pts Wait 5 days before grain
harvest.
-------------------------------------------------------------------------
Malathion (ULV) 0.6 8 fl oz Do not harvest for 5 days.
-------------------------------------------------------------------------
Methyl 0.5 1 pt Aerial application only. Do
parathion 4EC* not apply within 15 days of
small grains harvest or
within 12 days of corn
harvest. Do not enter
treated fields within 48
hours after application.
Fields must be posted.
-------------------------------------------------------------------------
Penncap-M* 0.5 to 0.75 2 to 3 pts Do not apply within 12 days
of harvest. Do not enter
treated fields within 48
hours after application.
Fields must be posted.
-------------------------------------------------------------------------
Warrior* 0.02 to 0.03 2.56 to 3.84 Do not apply within 21 days
fl oz of harvest. When applying by
air, apply in a minimum of 2
gallons of water per acre.
-------------------------------------------------------------------------
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A-1130, May 1997
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