Corn Production Guide (continued)
A-1130, May 1997
Insect Management in Corn (continued)
Wireworms
Wireworms are the immature stage of click beetles (Family:
Elateridae). The larvae are hard, brownish-orange, shiny, slender
worms. They bear six short, thin legs behind the head. The last
body segment is forked or notched. Mature larvae are about � to
1 inch long. Wireworms are most likely to be problems when corn
follows pasture or grassland. Continuous corn has developed
problems in the past, also. Infestations often are found in
coarse textured soils (sandy loam) where moisture is abundant,
perhaps in low spots of fields.
Threshold
There is no easy way to estimate wireworm infestations. Two
methods are currently used.
Soil Sampling — Sample 20 well spaced, 1
square foot sites to a depth of 4 to 6 inches for every 40 acres
being planted. If an average of one wireworm per square foot is
found, treatment would be justified.
Solar Baiting — In September, establish
bait stations for two to three weeks before freeze. Place bait
stations randomly through the field, but representing all areas
of the field. There should be 10 - 12 stations per 40 acre field.
Place one cup wheat and one cup shelled corn in a 4 to 6 inch
deep hole. Cover grain with soil and then an 18 inch square piece
of clear plastic. Dig up the grain. If an average of one or more
wireworm larvae are found per station, treatment would be
justified
Dosage in LB Product Rate
Insecticide AI 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 varies by 8 oz/1,000 ft Apply in a 7-inch band or
15 G* row spacing or row in-furrow at planting. 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 15 G varies by 8 oz/1,000 ft Apply in a 7-inch band at
row spacing of row planting. Do not apply in
contact with seed. Do not
exceed 27 lbs of product per
acre. Dyfonate aids in the
suppression of wireworms.
-------------------------------------------------------------------------
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
of row and 3G: shoe in front of the press
4 to 5 oz/1,000 wheel. Do not rotate to
ft of row another crop within 30 days
after application.
-------------------------------------------------------------------------
Fortress varies by 2.5 G: 6 oz/ Apply as a T-band or in-
2.5 G* and row spacing 1,000 ft of row; furrow at planting. Do not
5 G* 5 G: 3 oz/1,000 apply as a surface band
ft of row behind the press wheel.
Granules exposed on the soil
surface must be
incorporated. Crop
rotational intervals:
corn - anytime;
other crops - 30 days.
For wireworms, the in-furrow
application provides optimal
control.
-------------------------------------------------------------------------
Lorsban 15 G varies by 8 to 16 oz/1,000 T-Band or in-furrow at
row spacing ft of row planting. If high wireworm
numbers are anticipated, add
insecticide seed treatment
to planter box to augment
control
-------------------------------------------------------------------------
Lorsban 4E 2 4 pts Broadcast ppi in sufficient
water to the soil surface
and incorporate into the
soil.
-------------------------------------------------------------------------
Mocap 20 G* varies by 6 oz/1,000 ft Apply in a 7-inch band at
row spacing of row planting. Do not apply in
contact with seed.
-------------------------------------------------------------------------
Thimet 20 G* varies by 6 oz/1,000 ft Place granules in a 7-inch
row spacing of row band over the row directly
behind the planter shoe in
front of the press wheel. Do
not use in-furrow
application.
-------------------------------------------------------------------------
White Grubs
White grubs that are destructive to field crops in North
Dakota have a three year life cycle. In southeastern North
Dakota, the most common white grub pest occurs in continuous
cropping situations at sites where willow and cottonwood trees
are present. In other areas of the state, white grubs are most
likely to be found when rotation from grassland, pasture, or
grassy weed sites occur. Most root feeding occurs in the second
year of the life cycle. In most cases, the number of second year
grubs will only be great enough to justify control once every
three years.
Threshold
Treatment is recommended when sampling indicates an average of
one or more white grubs per square foot are found. The following
sampling procedure provides treatment decisions based on this
guideline.
Soil sampling — Sampling in late summer or
early fall, before a freeze, provides a more reliable estimate of
populations than spring sampling just before planting. Take soil
samples, 1 square foot in size to a depth of 8 inches. Begin
taking samples 45 yards from shelterbelts. A total of 30 samples
per field, randomly spaced along the shelterbelts are necessary.
If at least a single grub is found in less than 40% of the
samples, treatment may be required only out 20 yards from the
tree line. If 40 to 60% of the samples are infested, treatment is
needed to this distance and maybe as far as 65 yards. If greater
than 60% of the samples are infested, treatment may be needed out
to 90 yards from the tree line.
Dosage in LB Product Rate
Insecticide AI 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 to 16 oz/1,000 Apply in a 7-inch band (1
row spacing ft of row to 2 lb rate). Do not exceed
spacing 8.7 lbs of product per acre.
Do not apply Accent or
Beacon herbicide to corn
treated with Counter 15 G.
-------------------------------------------------------------------------
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 of in-furrow behind the planter
row and 3G: shoe in front of the press
4 to 5 oz/1,000 wheel. Do not rotate to
ft of row another crop within 30 days
after application.
-------------------------------------------------------------------------
Fortress varies by 2.5 G: 6 oz/ Apply as a T-band or
2.5 G* and row spacing 1,000 ft of row in-furrow at planting. Do
5 G* 5 G: 3 oz/1,000 not apply as a surface band
ft of row behind the press wheel.
Granules exposed on the soil
surface must be
incorporated. Crop
rotational intervals:
corn - anytime;
other crops - 30 days.
For white grubs, the
in-furrow application
provides optimal control.
-------------------------------------------------------------------------
Lorsban 15 G varies by 8 to 16 oz/1,000 Apply in-furrow at planting
row spacing ft of row time. (NDSU research
indicates that Lorsban aids
in white grub suppression.
With heavy white grub
infestation, some stand
reduction may still occur.)
-------------------------------------------------------------------------
Bt-Corn and European Corn Borer
Seed companies are now marketing Bt-corn hybrids. These
hybrids produce an insecticidal protein from a bacterium, Bacillus
thuringiensis, inside the corn plant to provide insect
control. The use of Bt-corn has the potential to provide
unique, easier, more consistent control of the European corn
borer (ECB).
What is Bt?
Bacillus thuringiensis is a naturally occurring
soil-borne bacterium found worldwide. Bt produces a
crystal-like protein that kills specific groups of insects. These
crystals are stomach poisons that must be ingested to provide
effective control. The toxic proteins disrupt the intestinal
membranes of the larvae, leading to their death.
There are several strains of Bt, each with different
spectrums of activity. The first Bt-corn hybrids contain
Cry1Ab or Cry1Ac Bt proteins. These have activity against
ECB.
The Creation of Bt-corn and Its Impact on Corn Insect
Pests
The DNA portion responsible for producing the toxin is
extracted from the Bt bacterium. This DNA is inserted into
the corn plant's DNA. The DNA is inserted as a genetic package
which includes the Bt protein gene, a genetic marker
(allows for identification of successful transfer), and a
promoter (controls where the toxin is produced in the plant). The
transformation, or event, is observed for toxin production levels
and the abscence of detrimental impacts on yield or other
important agronomic traits.
The level of control of ECB is dependent on the Bt
event. Currently, there are three unique events that have been
registered by EPA for commercial use. The three events are: 176
(Ciba Seeds, and Mycogen), MON810 (Monsanto), and Bt-11 (Northrup
King). Event 176 is trademarked as "Maximizer" by Ciba
Seeds and "NatureGard" by Mycogen. Both the Monsanto
and Northrup King events are trademarked as
"YieldGard".
An important difference between event 176 and the Bt-11 and
MON810 plant material is that the Bt toxin expressed in
the 176 hybrids is limited to green tissues, while YieldGard
hybrids express Bt in many of the reproductive tissues,
such as tassel and silk, as well as green tissues. YieldGard
hybrids have the potential to provide higher control levels of
late-season ECB. Early field trials in neighboring states have
shown that despite higher numbers of late-season ECB surviving on
the 176 hybrids, final yield data is still favorable.
Regardless of the Bt event, growers should still select
corn hybrids based on overall yield performance in their region.
Selecting a Bt-hybrid only for ECB control will not
guarantee higher yields compared with other conventional hybrids.
The Bt gene can only enhance the yield potential of a
hybrid when ECB are present.
Current Bt-corn hybrids have no activity on aphids,
spider mites, corn rootworms, cutworms, grasshoppers, or stalk
borer. Field studies evaluating the hybrids impact on armyworms
is limited.
Performance of Bt-corn
General observations made on performance of these hybrids
found that the Bt hybrids dramatically reduce first
generation ECB. Hybrids differed in the levels of control of
late-season or second generation ECB; some survival and tunneling
were observed in those hybrids with the 176 event. Yields varied;
the presence of the Bt gene was not a guarantee of higher
yields. Some unprotected, non-Bt hybrids yielded better
than Bt hybrids. However, the Bt hybrids out
yielded their unprotected counterparts.
Before deciding to use a Bt hybrid, compare yield
results from corn hybrid performance trials in your area. Bt
hybrids suitable for use in North Dakota and surrounding regions
are currently being developed and evaluated.
Seed Rots and Seedling Blights (various fungi)
Description: Seed may rot before germination or
shortly after, resulting in no seedling emergence, or
seedlings may emerge and turn yellow and wilt. Aggravated by
poorly drained soils, cold and wet soils, compacted soils,
deep planting, and quality of seed.
Management: Injury-free seed of high quality and
germination percentage should be planted. Seed treatments
will reduce the risk of seedling blight and seed rot. Most
corn seed is sold pre-treated with fungicides. However,
further information on corn seed treatments registered in
North Dakota may be found in NDSU Extension publication
PP-622, Field Crop Fungicide Guide. Good cultural practices
and seedbed preparation reduce the risk.
Common Leaf Diseases
Eyespot (Kabatiella zeae)
Description: Very small (1/16 to 1/8 inch),
translucent circular to oval spots with yellow halos. Initial
spots water-soaked; spots later develop brown or purple
border.
Management: Crop rotation away from corn; tillage
to bury residue.
Northern Corn Leaf Blight (Helminthosporium
turcicum)
Description: Large elliptic water soaked lesions on
leaves which soon turn straw colored to dark brown.
Management: Choose hybrids with good resistance.
Use crop rotation and tillage to bury residue.
Common Rust (Puccinia sorghi)
Description: Red eruptions (pustules) on leaf
surface contain thousands of rust spores.
Management: Hybrids vary in resistance; rarely
serious enough to warrant additional control.
Gray Leaf Spot (Cercospora zeae-maydis)
Description: Disease occurs in warm to hot, humid
seasons. Lesions are pale brown or gray to tan, long (� to 2
inches), narrow and rectangular, characteristically
restricted by the veins. Losses have been severe in some Corn
Belt states in recent years. Fungus survives in corn
residue.
Management: Variation in hybrid susceptibility
exists. Fungicide protection may be warranted for high value
fields under severe disease pressure.
Holcus Spot (Psuedomonas syringae)
Description: Small, irregular shaped spots, with a
water-soaked appearance at first, followed by spots turning a
creamy white to tan, resembling parchment paper. Favored by
warm, wet weather and winds.
Management: Crop rotation reduces overwintering of
bacteria. Seldom serious as weather turns too hot or dry to
be favorable for continued infection.
Maize Dwarf Mosaic (Maize Dwarf Mosaic Virus)
Description: Light green mottle or mosaic forms on
upper leaves. Upper portion of plant may be stunted.
Management: Hybrids may vary in susceptibility.
Rare in Northern climates. Transmitted by aphids that must
move into area from states farther south.
Stalk and Ear Diseases
Common Smut (Ustilago maydis)
Description: Leaves, stalks, ear, or tassels may be
replaced by black spore mass which is covered by a persistent
grayish membrane. "Boils" or irregular growths
common.
Management: Trace of smut usually found in every
field. Hybrids vary in susceptibility. Hail damage or various
stresses increase risk of smut.
Head Smut (Sphacelotheca reiliana)
Description: Spores infect plant systemically while
in seedling stage, causing possible stunting, but only
tassels and ears are smutted. Black spore masses covered with
only a thin membrane which easily breaks up (in contrast to
common smut). Thread-like strands occur in the spore masses.
Management: Crop rotation reduces risk of
infection. Most hybrids resistant.
Ear Rots (various fungi)
Description: Kernels of ears turn pink to red to
black with associated mold growths. Often associated with
insect injuries or with other injuries and very wet weather.
Management: Hybrids vary in resistance to ear
molds. Crop rotation reduces risk of exposure to fungi.
Reducing insect damage may also reduce ear mold damage.
Stalk Rots (various fungi)
Description: Stalks are weak; the pith is shredded
and discolored, often pink to red. Lodging frequently occurs.
Yield losses occur due to poor filling of ears, early ear
drop, and stalk breakage.
Management: Crop rotation to non-cereal crops is
beneficial. Proper management of soil fertility reduces stalk
rots. Hybrids vary in resistance to stalk rot as well. If
stalk rot present, harvesting early reduces ear loss.
Integrated Pest Management (IPM) for
Corn
Timely field scouting is the key to any successful pest
management program. Regular scouting of fields reveals the growth
stage of the crop, the condition of the crop, the identity of the
pests present, and the extent and severity of the pest. This
information is used to determine if a growing season control
measure is needed, the appropriate timing for such a measure, or
if another management step is needed at harvest or following
harvest.
One of the tools that may help in timely field scouting is the
use of a pest management calendar. An example of a corn pest
management calendar is given. These calendars have
been developed for many crops to indicate when certain pests are
most likely to be observed in a field, according to calendar date
and crop growth stage. For example, cutworms in corn in North
Dakota should be scouted for between May 1 and June 30, while
armyworms attack corn later and should be scouted for between
June 15 and September 15. Keep in mind that these dates are
general guidelines and may vary slightly each year, depending on
planting dates and growing season weather conditions.
Preparations of Samples for Plant
Diagnostic Lab
Samples of diseased or injured plants and corn insect pests
may be sent for diagnosis to:
Plant Pest Diagnostic Laboratory
Box 5012
North Dakota State University
Fargo, ND, 58105.
Mailing instructions: INSECTS: Send small ones in vial
of alcohol; never in envelope. Pack large insects such as moths
in cotton. Insects should be dead. PLANTS: Collect as much of
plant as possible, several entire plants if feasible. May be
placed in a plastic bag which is folded over loosely, but not
sealed tightly. DO NOT add moist towels as specimen will
decompose. If possible, place some leaves flat in paper envelope
and rest of plant and leaves in plastic bag.
A fee ($8-$10) is charged for diagnosis; additional fees
charged if special tests are required or requested.
For purposes of disease management, corn should follow a
broadleaf crop whenever possible. Corn does not have any diseases
in common with broadleaf crops such as drybean, soybean, or
potatoes. Use of corn in rotation with these crops helps break
the disease cycle of organisms that attack corn and those that
attack the broadleaf crops.
Corn has some important and damaging diseases in common with
other cereal crops, such as wheat, barley, oats, millet or
sorghum. The Gibberella (Fusarium graminearum) stalk rot
of corn is caused by the same fungus that causes head scab in
wheat, barley and other small grains. This scab fungus survives
very well in corn residue, and planting wheat or barley back into
corn ground results in a high risk of head scab in the small
grain crops, if wet weather should occur during the flowering
period of the small grain crops. Corn following small grains is
not as severe a disease risk as wheat/barley/oats following corn,
although corn and small grains do have some root rot disease
organisms in common.
Leaf diseases, such as northern corn leaf blight and grey leaf
spot, are caused by fungi that survive in corn residue. Sorghum
and sudangrass are hosts of several corn diseases. Crop rotation
to breadleaf crops reduces the potential for corn leaf diseases
that survive in corn debris.
Corn is a high user of nutrients. Corn in the Northern Plains
is responsive to application of nitrogen (N), phosphorus (P),
potassium (K), sulfur (S) and zinc (Zn) if soil test levels
indicate less than adequate levels. Soil testing is recommended
to predict the probability of response of corn to soil nutrient
levels. Soil test cores should be taken at 0-6 inch and 6-24 inch
levels. N and S should be analyzed on both core depths. P, K and
Zn is analyzed on the surface depth. Salt levels may be analyzed
on both depths if salt problems are anticipated.
Nitrogen
Nitrogen deficiency of corn is characterized by yellowing of
the lower leaves in a pattern that begins at the leaf tip and
extends down the midrib until the entire leaf turns yellow, then
brown in extreme deficiency situations.
Nitrogen recommendations for corn are based on the formula:
N recommended = 1.2 X Yield Goal (bu/acre) - STN - SDA -
PCC
where STN is soil test N to 2 ft.
SDA is sampling date adjustment of 1/2 lb N/day if sampled
before September 15.
PCC is previous crop credit, usually from a legume
Nitrogen for corn may be applied preplant or sidedressed
before or after emergence. Some N may be applied at planting, but
banded rates are restricted by the sensitivity of corn to
salt/ammonia damage and no more than 10 lb/acre of N + K2O
with the seed. If higher levels of banded fertilizer are desired,
than the fertilizer and seed must be separated. A band 2 inches
beside and 2 inches below the seed is often used to apply higher
rates of fertilizer. A total fertilizer program can be applied in
a separated band, but when fertilizer N rates exceed about 50 lb
N/acre, corn roots have difficulty taking up P for several weeks.
It is therefore recommended to apply less than 50 lb/acre N in a
banded application and apply the rest of the N in a separate
application.
High levels of N increase protein content of the kernel
somewhat but also increase susceptibility to green snap during
periods of rapid growth potential. Over-fertilization with N is
therefore discouraged, although adequate levels of N are
important for yield.
Phosphorus
Phosphorus deficiency symptoms are characterized by purpling
of lower leaves, especially early in the season. Purpling may not
always be related to low soil P levels but may be related to
decreased ability of the plant to take up P due to root growth
restrictions, including cold soil temperatures, wet soils or
compaction. Some corn varieties are also more likely to display
purpling than others.
Recommended rates of broadcast P fertilizer are shown in Table
1. Banded rates of P may be reduced by 1/3 if soil test levels
are low or very low, because these rates include additional P for
buildup. Reducing P levels may be economical in the short-term
but will not buildup levels over the long-term. Sustaining high
levels of production is most likely if soil test levels are built
to at least medium P levels.
Fallow syndrome is a condition thought to be caused by reduced
populations of soil fungi called mycorrhiza. After black fallow,
or following sugarbeet, mycorrhiza levels are reduced. Mycorrhiza
aid corn plants by infecting roots and acting as root hairs to
facilitate the uptake of nutrients, expecially P, into the plant.
In return, the corn plant supplies the fungi with organic
nutrients. This relationship is called symbiosis- a relationship
that is mutually beneficial to both organisms. In most rotations,
such as soybean-corn-wheat, mycorrhiza levels are maintained.
However, when soil remains bare, or after sugarbeet, myccorhiza
levels are lowered. High rates of P are required for corn
following fallow or sugarbeet.
Potassium
Recommended rates of broadcast K are shown in Table 2.
Although many of the soils in the region are high in K, low K
soils are common in some areas. Sandy soils on uplands are
especially low in K. K deficiency may be observed as yellowing on
the lower leaf margins, gradually moving inward toward the midrib
of the leaf, and up the plant. Both younger and older plants may
display K deficiency. Plant K levels may be reduced in high K
soils when soils are droughty or are drier due to ridge-till. In
these soils, some K may be helpful in a 2 by 2 inch banded
application, or in a deep band method of application in moister
soils to supply K in a more concentrated form.
Sulfur
Sulfur deficiency of corn is not common but may sometime be
seen in coarser soils with lower organic matter levels.Sulfur
deficiency is seen as yellowing of the upper leaves. Sulfur soil
test levels of 16 lb/acre S in the surface 2 ft. would be
considered likely to respond to S applications. Fertilizers with
available sulfate, such as ammonium sulfate or ammonium
thiosulfate would be expected to perform more efficiently as an S
source than some other elemental forms.
Zinc
Zinc deficiency is common in some areas because of low native
soil zinc levels. Crops in soils with zinc levels of 0.6 ppm or
lower may be expected to respond to Zn. Zinc deficiency symptoms
include yellowing or whitening of the leaf tissue between the
leaf margins and midrib. The symptoms are usually greatest on
younger leaves. Foliar sprays of zinc sulfate, zinc chelate or
ammoniated zinc solutions are helpful early in the season.
Deficiency symptoms may be avoided by applying 3-5 lb/acre actual
Zn as zinc sulfate preplant incorporated, or by adding zinc
chelate or other zinc fertilizers in the planter banded
treatment.
Chloride
Recent research in the eastern US has reported yield responses
and lowered stalk lodging when chloride was applied to low
chloride soils. This research has not been attempted in North
Dakota, but it is curious that despite locally high levels of K,
stalk rot damage is still a considerable problem in the region.
Perhaps lower stalk rot reported in the lower midwest with K
application is not just a response to K, but to application of K
plus chloride in the 0-0-60-49Cl usually applied in such trials.
For producers with chloride levels below 30 lb/acre in the
surface 2 ft., application of chloride may be tried on a trial
basis. Again, no North Dakota research has been attempted yet to
verify these early reports.
Salts
Corn is moderately susceptible to salt damage. Certain
varieties show more susceptibility to damage than others. Check
with your seed supplier for information on sus-ceptibility.
Because salts are not a normal occurance in the lower midwest,
evaluations are only available locally. Encourage your seed
company to screen for this problem wherever possible.
Table 1. Phosphate recommendations for grain corn.
| |
|
Soil Test Phosphorus,
ppm |
| |
|
VL |
L |
M |
H |
VH |
| Yield |
Bray Pl |
0-5 |
6-10 |
11-15 |
16-20 |
21+ |
| Goal |
Olsen |
0-3 |
4-7 |
8-11 |
12-15 |
16+ |
| bu/A |
|
- - - - - - - - - - - - lb
P2O5/Acre
- - - - - - - - - - - - |
| 50 |
|
30 |
25 |
15 |
0 |
0 |
| 100 |
|
65 |
45 |
25 |
10 |
0 |
| 150 |
|
95 |
70 |
40 |
15 |
0 |
| 300 |
|
125 |
90 |
55 |
20 |
0 |
Table 2. Potassium recommendations for grain corn.
| |
|
Soil Test Potassium,
ppm |
| Yield |
|
VL |
L |
M |
H |
VH |
| Goal |
|
0-40 |
41-80 |
81-110 |
121-160 |
161+ |
| lb/A |
|
- - - - - - - - - - - - lb
K2O/Acre - - - - - - - - - -
- - |
| 50 |
|
50 |
35 |
20 |
10 |
0 |
| 100 |
|
100 |
75 |
45 |
15 |
0 |
| 150 |
|
155 |
110 |
65 |
20 |
0 |
| 200 |
|
205 |
145 |
85 |
25 |
0 |
[ NEXT ] [ Go to the Index ] [ BACK ]
A-1130, May 1997
NDSU Extension Service, North Dakota State University of
Agriculture and Applied Science, and U.S. Department of
Agriculture cooperating. Sharon D. Anderson, Director, Fargo,
North Dakota. Distributed in furtherance of the Acts of Congress
of May 8 and June 30, 1914. We offer our programs and facilities
to all persons regardless of race, color, national origin,
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