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Ministry of Agriculture, Food and Rural Affairs

European Corn Borer

European Corn Borer Entry Holes around Pepper Cap European Corn Borer Larva European Corn Borer Larva European Corn Borer Moths Milk Carton Trap Heliothis Trap
Click to enlarge.

Beginner

Scientific Name
Ostrinia nubilalis

Identification

  • Larvae are greasy-looking, grey-to-tan-coloured with small brown spots on each segment and a dark head
  • Full-grown borer larvae reach 2.5 cm (1 in.) in length
  • Adult moths are light brown with wavy lines across the wings
  • Larvae usually enter the fruit under the cap, leaving an entry hole with sawdust-like frass

Often Confused With
Pepper maggot

Period of Activity
Corn borers are present from mid-July through September. The second generation, and sometimes a partial third generation, attacks peppers. Peppers become susceptible to feeding when the fruit are the size of walnuts (3 cm or 1 1/4 in. in diameter).

Scouting Notes
Use pheromone traps to monitor adult flight activity. Fields can also be scouted for egg masses and feeding activity, but damage is easy to miss.

Thresholds
There is no tolerance for this pest in processing or fresh-market pepper crops.

Sara Simpkins photograph, All Rights Reserved.

Advanced

Scientific Name
Ostrinia nubilalis

The European corn borer attacks a large number of agricultural commodities in Ontario -- including corn, peppers, snap beans, potatoes, tomatoes and apples. In peppers, European corn borers are a concern during the time fruit are present.

European corn borer is the most important insect pest of pepper in Ontario.

Identification
The European corn borer larva is a light grey to tan colour with small dark spots on each body segment.  The head is brown to black.  Larvae reach up to 2.5 cm (1 in.) in length.

The adult is a light brownish moth, with patterns of wavy lines on the wings.

Larvae enter the fruit under the calyx (stem cap).  A yellowish-brown sawdust-like residue of droppings may be seen around the hole.  Larvae may also enter through the side of the fruit.  Fungi or bacteria may invade the entry hole, causing rot.

Often Confused With
Pepper maggot

Biology
This insect pest overwinters in Ontario as a full grown caterpillar in corn stover or other host plant debris, pupating in the spring and emerging as an adult in late May or early June.

There are two distinct pheromone races of ECB present in North America -- E or New York and Z or Iowa -- each of which responds to different pheromone blends.  In some locations, both races are present.  In Ontario, populations of ECB respond to the Iowa (Z) pheromone blend.

There are also distinct genetic strains (ecotypes) of corn borers– univoltine (northern), bivoltine (central) and multivoltine (southern)– which refers to the number of generations per year.  All strains of ECB overwinter as last instar larvae, so when a larva reaches maturity, it will either enter diapause (hibernate or overwinter) or pupate to become an adult.  Diapause is controlled by day length, temperature, genetics, and by the nutritional quality of host plants. Both the univoltine and bivoltine strains are present in Ontario.  In the southwestern counties of Essex, Kent and Elgin, the bivoltine strain completes two generations in most summers and can go on to a partial third generation in unusually warm years. In the rest of the province, the univoltine strain normally completes only one generation per year (but may begin a second generation in warm years). Both strains exist in significant numbers in a broad area of overlap including Lambton, Middlesex, Oxford, Brant, Haldimand-Norfolk, Hamilton-Wentworth and Niagara Counties.

Period of Activity
Corn borers are present from mid-July through September. The second generation, and sometimes a partial third generation, attacks peppers. Peppers become susceptible to feeding when the fruit are the size of walnuts (3 cm or 1 1/4 in. in diameter).

Scouting Notes
Adults can be monitored using black-light traps or pheromone traps. Heliothis or sticky traps (wing or milk carton models are often used) should be set up in un-mowed grassy areas near the field. Corn borers are attracted to sticky traps by the use of the Iowa or Z strain of lure. Check traps in your fields twice a week and replace lures every week or according to the manufacturer’s recommendation.

Heliothis traps are cheaper (over the long term) and more convenient to use.  However, while they work well for monitoring peaks in corn borer activity, they are poor at detecting low numbers of ECB, especially at the beginning of the flight period.  Milk carton traps provide better detection of low ECB activity.

Trap placement in the field is important.  Pheromone traps should be placed in areas with the highest likelihood of finding ECB moths.  After new adult moths emerge, they move to areas of dense vegetation– often grassy areas adjacent to fields– where they are able to find water (dew on plants) for drinking as well as suitable areas to rest and mate.  For this reason, pheromone traps are usually placed in these areas.

Trap height also affects the number of ECB moths caught.  Place traps such that the base of the trap is located approximately 15 cm (6 in.) below the canopy of the vegetation.

Fields can also be scouted for egg masses and feeding activity, but damage is easy to miss.

Thresholds
There is no tolerance for this pest in processing or fresh-market pepper crops.

Management Notes

  • The crop must be protected from the time fruit are “walnut sized” (3 cm or 1 ¼” in diameter) until harvest, if corn borer is present.
  • Place traps in the grassy (preferably un-mowed) area at the edge of a field.  If possible place traps near a field that was in corn the previous year.
  • For milk carton traps, use 3-5 milk traps per field, placed at least 15 m (50 feet) apart.  Mount cartons on stakes roughly 1 m (3 feet) above the ground.  Secure traps with rubber bands or twist tie material.
  • The bottom of a Heliothis trap should be at least 0.5 to 1 m (1 ½- 3 feet) above ground level.
  • ECB pheromones degrade rapidly.  Replace entire milk carton trap including the lure once a week.  For Heliothis traps, replace the lure weekly.
  • Choose trap sites that are easy to reach in all weather conditions, but that will not impede farm operations. 
  • Do not place traps within 200 m (650 feet) of any other type of pheromone trap.

Sara Simpkins photograph, All Rights Reserved.