The European corn borer is one of the most important insect pests of sweet corn in Kentucky. The larval stage tunnels into corn stalks and ear shanks, and will feed on kernels in the ear. The severity of corn borer infestations varies from year to year and even from field to field on the same farm.
The European corn borer has two generations each year and occasionally a partial third. Mature larvae spend the winter in corn stalks and stubble. In late April or early May of the following year, the larvae transform to the pupal stage. The resulting adults, or moths, emerge from the pupal cases, mate and begin to lay eggs. Female moths fly and lay their eggs at night. Cool temperatures, strong winds or driving rains will reduce or stop their activity.
First generation moths are attracted to early planted corn. Their eggs are laid in masses of 15 to 35 eggs on the underside of corn leaves. Each female is capable of laying an average of two egg masses a night for about 10 nights. These eggs begin to hatch in 5 to 6 days. The presence of a dark black spot in the egg means that it will hatch very soon. Newly hatched larvae, about 1/8-inch long, will move from the leaf into the whorl of the plant to feed for several days. When the larvae become about 3/4-inch long, they will enter the stalk to complete their development. The mature larvae usually pupate within the tunnel; however, some of the reddish brown pupae may be found in leaf axils or elsewhere on the plant. Moths will emerge from these pupae in 2 to 3 weeks and lay their eggs to start the second generation. late planted corn is most susceptible to Damage from this generation of borers.
Controls
Biological: Several parasites and predators attack the European corn borer during the growing season. Ladybird beetles and other predators feed on eggs and small larvae. Some parasitic flies and wasps have been imported to aid in control, but the results have been limited. Their importance in regulating corn borer populations is not known at this time.
Bt sweet corn hybrids (Attribute™) provide effective full season control of European and southwestern corn borer. To a limited extent, some sweet corn producers have tested Bt sweet corn for local fresh market sales, but
use of Bt sweet corn hybrids for European corn borer control comprise less than 1% of the sweet corn market
Cultural: Stalk Destruction. European corn borer larvae spend the winter in corn stalks. Many larvae can be killed if the stalks and field debris are plowed under. However, no information indicates that clean plowing or
shredding of stalks will actually lower corn borer damage the following year. Therefore, low cutting or shredding are recommended only if they fit sound soil conservation practices. Planting date is very important in determining the potential for European corn borer infestation. Extremely early or late planting will increase the potential for borer damage. The first generation can be very damaging to early plantings, while late planted fields are prone to attack by the second. The second generation is usually more damaging to sweet corn than the first.
Monitoring: In whorl stage corn, treat if more than 15% of the whorls are infested with live larvae. It is very important to monitor late whorl stage sweet corn for European corn borer, because as the tassel begins to emerge, corn borer larvae will move to other locations on the plant, the ear being potentially one of those. Corn borer control is frequently necessary when tassels begin to emerge from the whorl. During silking, pheromone traps are used to determine the need and frequency of insecticide sprays to protect the ear. Separate pheromone traps are needed for corn earworm, fall armyworm, southwestern corn borer, and European corn borer during this silking period.
Application Alternatives:
Ambush 2 E (permethrin)- Apply as a foliar application at 6.4 to 12.8 fl oz per acre to a limit of 76.8 fl oz per acre per season.
Asana XL (esfanvalerate)- Apply as a foliar application at 5.8 to 9.6 fl oz per acre to a limit of 96 fl oz per acre per season.
Baythroid 2 (cyfluthrin)- Apply as a foliar application at 1.6 to 2.8 fl oz per acre to a limit of 10 applications per season.
Capture 2E (bifenthrin) - Apply as a foliar treatment at 2.1 to 6.4 fl oz per acre to a limit of 12.8 fl oz per acre per season. The long Restricted Entry Interval limits the use of this product to machine harvested field for
processing. Only a small fraction of the acreage in Kentucky is harvested by machine.
Bt-products (various labels)- Apply as a foliar treatment and reapply as necessary.
Lannate 90 SP (methomyl)- Apply as a foliar treatment at 1/4 to ½ lb per acre to a limit of 8 lb per acre per season.
Pounce 3.2 EC (permethrin)- Apply as a foliar treatment at 4 to 8 fl oz per acre to a limit of 48 oz per acre per season.
Sevin 80 WSP (carbaryl)- Apply as a foliar treatment at 1-7/8 to 2-½ lb per acre to a limit of applications per acre per season. Allow at least 7 days between sprays.
Warrior 1 EC (lambda-cyhalothrin)- Apply as a foliar treatment at 2.56 to 3.84 fl oz per acre to a limit of 3.84 pt per acre per season.
Southwestern Corn Borer
(Diatraea grandiosella)
The southwestern corn borer is another ear feeding and stalk boring insect pest of sweet corn in the western half
of Kentucky. The larval stage tunnels into corn stalks and ear shanks, and will feed on kernels in the ear. Like the
European corn borer, southwestern corn borer has two generations each year. Mature larvae spend the winter
below ground in the rotting crowns of the harvested corn. In early May of the following year, the larvae
transform to the pupal stage. The resulting adults, or moths, emerge from the pupal cases, mate and begin to lay
eggs in mid June. Each female is capable of laying an average of two egg masses a night for about 10 nights.
These eggs begin to hatch in 5 to 6 days. The presence of three red stripes on each egg means that it will hatch
very soon. Newly hatched larvae, about 1/8-inch long, will move from the leaf into the whorl of the plant to feed
for several days. When the larvae become about 3/4-inch long, they will enter the stalk to complete their
development. The mature larvae usually pupate within the tunnel. Moths will emerge from these pupae in 2 to 3
weeks and lay their eggs to start the second generation. Late planted corn is most susceptible to damage from this
generation of borers.
Controls
Biological: The predators and parasites of southwestern corn borer in Kentucky are not well understood.
Bt sweet corn hybrids (Attribute™) provide effective full season control of European and southwestern corn
borer.
Cultural: Many larvae can be killed if the stalks and field debris are plowed under. However, most of the moths
are emerging from field corn of which most is in no-till for soil conservation reasons.
Planting date is very important in determining the potential for southwestern corn borer infestation. Extremely
early or late planting will increase the potential for borer damage. The first generation can be very damaging to
early plantings, while late planted fields are prone to attack by the second. The second generation is usually more
damaging to sweet corn than the first.
Monitoring: In whorl stage corn, treat if more than 15% of the whorls are infested with live larvae. It is very
important to monitor late whorl stage sweet corn for southwestern and European corn borer, because as the tassel
begins to emerge, corn borer larvae will move to other locations on the plant, the ear being potentially one of
those. Corn borer control is frequently necessary when tassels begin to emerge from the whorl.
During silking, pheromone traps are used to determine the need and frequency of insecticide sprays to protect the
ear. Separate pheromone traps are needed for corn earworm, fall armyworm, southwestern corn borer, and
European corn borer during this silking period. The southwestern corn borer pheromone trap is very effective
with some weekly counts exceeding 1000 moths per trap in some areas.
Bt sweet corn is highly effective in controlling European and southwestern corn borer in Kentucky. To a limited
extent, some sweet corn producers have tested Bt sweet corn for local fresh market sales, but use of Bt sweet
corn hybrids for European corn borer control comprise less than 1% of the sweet corn market.
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