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Description
Corn is rich in nutrition, in addition to containing a variety of nutrients, including protein and fat than rice, noodles and Hamish, fat half of linoleic acid, and lecithin, vitamin A, E etc.. Linoleic acid can reduce cholesterol, prevent its deposition in the vascular wall, on the prevention of hypertension, cardiovascular and cerebrovascular diseases have a positive effect.
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High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
Sweet Corn XXXVI
Corn Earworm
Whitney S. Cranshaw
Corn Earworm
Identification (and life cycle/seasonal history)
Corn earworm is, by far, the most common species of caterpillar found in sweet corn ears
and the only species found west of the Rockies. In the High Plains, European corn borer,
western bean cutworm and, in the south, southwestern corn borer are sometimes also
found in corn ears. However corn earworm is the key insect pest of the crop in most
areas. Corn earworm is also an important pest of many other crops including tomatoes,
peppers, and tomatillos. In these crops it is commonly referred to as tomato fruitworm.
Corn earworm winters as a pupa about 3 to 5 inches deep in soil. Successful wintering in
the region regularly occurs in western Colorado and much of eastern Colorado, south of
approximately I-70. However, mild winters can allow survival further north.
Overwintered populations are supplemented by migrants from the southern US, which
annually spread throughout the US. Late spring frosts can cause significant mortality of
early-emerging moths.
Corn earworm moths are buff-colored and similar in size to other moths of the cutworm
family. Females lay eggs singly (not in masses) on green silks of sweet corn. Eggs can
hatch in a few days and the larvae move into the ear, feeding originally on green silk.
Later the larvae tunnel into maturing kernels. Corn earworm caterpillars are very
cannibalistic and rarely is more than one caterpillar found in a single corn ear. Following
egg hatch the caterpillars develop for a period of two to three weeks before becoming full
grown. They cause increasing damage as they get older and larger. When feeding is
done, they drop to the soil and dig a cell where they pupate.
Plant Response to Damage
Early season corn earworm feed in the whorl of sweet corn plants causing damage that
sometimes resembles that of early season European corn borer. The amount of earworm
pressure on sweet corn ears may sometimes be predicted from the number of whorl
feeding earworm in the field prior to ear formation.
High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
Ear feeding corn earworm caterpillars tend to limit feeding damage to the ear tip, and this
area can be extensively damaged. Entry by this insect into the side of the ear occurs
occasionally, but it is more common with other caterpillars found in sweet corn.
Wounding by corn earworm provides an entry court for some kernel-rotting fungi. Some
insects, notably sap beetles, readily invade sweet corn ears through corn earworm
wounds.
Management Approaches
Biological Control
Corn earworms are natural affected by several biological controls. Probably most
important are general predators common to corn - minute pirate bugs, lady beetles, and
green lacewing larvae. Fungal diseases can occasionally impact corn earworm
populations. However, these can not consistently suppress corn earworm below
damaging levels. Furthermore, natural enemy populations in sweet corn are greatly
reduced by insecticide applications made to the crop.
Cultural Control
Plowing of fields should kill many of the overwintering pupae. However, this insect is
highly mobile and migratory reinvasion from distant sources can be expected. Some
sweet corn varieties with tight husks around the ear tip are slightly resistant to corn
earworm, but injury can also occur to these varieties. Transgenic varieties that express
the Bt-toxin in the silk can suppress corn earworm, but these are currently available in
limited quantities.
Sampling
The size of adult flights of corn earworm can be good predictors of the intensity of later
larval infestation. Corn earworms are readily attracted to blacklight monitoring traps.
There are also very effective pheromone lures for males. However, since corn earworm
is a strong flier it is not often captured efficiently in standard sticky-bottomed traps.
Instead cone-shaped 'Heliothis' traps are used for this species. The pheromone of the
corn earworm is also fairly unstable and needs replacement every few weeks.
Corn earworm pheromone trapping is a useful tool in determining spray schedules. If
good records are kept and monitoring methods remain constant then changes in captures
at traps become good predictors of infestation levels.
Spray programs in western Colorado are based on pheromone captures. Experience has
showed that if corn earworm captures exceed a certain level, moving from a three to a
two day spray interval is necessary to maintain control. If a higher threshold is reached,
an insecticide with ovicidal properties is added to the spray. Treatment thresholds were
developed with trial and error over several years, and have been lowered as problems
appeared. Treatment thresholds will vary for different areas and production systems.
High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
Chemical Control
Sweet corn becomes attractive to corn earworm egg laying when green silks first emerge.
These silks are where corn earworm lay their eggs. Sweet corn produces silk
continuously until harvest, so there are always attractive oviposition sites on the ear. The
target for corn earworm applications are eggs and/or newly hatched larvae before they
enter the ear tip. Regularly scheduled insecticide applications are necessary to provide
residual on the newly grown silk near the tip of the ear. When many corn earworm moths
are laying eggs, a two or three day spray schedule may be necessary to provide good
control. Regular sprays may be needed until within two or three days of harvest to
eliminate larval damage.
Problems with control of corn earworm have been observed in many locations. This can
have many possible causes: 1) Beginning the spray schedule too late. The initial sprays
should be applied as the first silks appear within a field. 2) poor coverage of the ear tips,
3) extremely heavy egg laying during periods of high populations, 4) improper spray
schedules, 5) resistance to the insecticide used. Corn earworm is beginning to become
resistant to pyrethroid insecticides over much of its range. Rotation with insecticides in
different pesticide classes with different mode of action is recommended.
Honeybee hazard caution: Honey bees will forage for corn pollen and applications
made during pollen shed have risk to area honey bee hives. Avoid using products of
highest hazard to honey bees (e.g., Penncap-M, certain carbaryl formulations) and work
with area beekeepers to limits pesticide application hazards to sweet corn.
Product List for Corn Earworm on Sweet Corn:
Insecticide Lbs Active Ingredient Per Acre Preharvest Interval, Remarks
(Fl oz or oz. product)
Baythroid 2 0.025-0.044 lb (0.8-1.6 fl oz.) (0 day, 12 hour reentry) Pyrethroid
insecticide. Maximum amount
allowed in 7-day interval 2.8 fl.
oz/A
Warrior 0.02-0.03 lb (2.56-3.84 fl. oz.) (1 day, 24 hour reentry) Pyrethroid
insecticide. Maximum application
of 0.25 lb AI/acre per season of
3.84 pt/acre of product per season
Asana XL 0.03-0.05 lb (5.8-9.6 fl. oz.) (1 day, 12 hr reentry) Pyrethroid
insecticide. Maximum application
of 0.25 lb AI/acre per season.
Avaunt 0.045-0.065 lbs ai (2.5-3.5 oz) (3 days. 12 hrs reentry machine
harvest, 14 days for hand harvest)
Carbamate insecticide. Do not use
more than 14 oz product per acre in
growing season. Minimum 3 day
interval between applications.
Mustang, Fury 0.035-0.05 lb (3.0-4.3 fl. oz.) (3 days PHI, 12 hr reentry)
Pyrethroid insecticide. Maximum
High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
0.3 lbs ai/acre per season.
Larvin 3.2 0.5-0.75 (20-30 fl. oz.) (0 day, 48 hour reentry) Carbamate
insecticide. Maximum application
of 300 fl. oz./acre per season.
Lannate 2.4LV (1-1 1/2 pt) (1 day PHI, 48 hours reentry).
Lannate 90SP (1/3-1/2 lb) Carbamate insecticide. Maximum
application of 6.3 lbs AI/acre per
season. Has some activity against
eggs.
Success, (3-6 fl. oz.) (1 day) Naturalyte insecticide.
SpinTor Maximum application of 16 fl.
oz/acre per season.
Entrust (1-2 oz.) (1 day) Naturalyte insecticide.
Formulation suitable for Certified
Organic production. Maximum
application of 9 oz/acre per season.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary
to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of
products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services
can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions
and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules
and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules,
regulations and allowances applicable in your state and locality.
Categories: Sweet Corn, Insects, Corn Earworm
Date: 01/26/2004
High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and
Montana State University.
