Pepper IPM: European Corn Borer

Life cycle and damage

The European corn borer (ECB) has more than 200 host plants, which include many common weeds and crops. ECB is the most important insect pest of peppers in New England. Prior to setting fruit, only an occasional pepper plant suffers injury to stems or branches. Later in the season, ECB larvae cause extensive fruit loss in most pepper fields. Bells and other sweet or mild varieties suffer higher infestations than hot peppers. As a general rule, the hotter the pepper, the less threat there is from corn borers.

Adult females are a light yellowish-tan, about inch long, with wavy lines across the wings. Females lay flat, translucent white egg masses in batches of five to 30 eggs, about 1/4 to 1/2 inch across, on the underside of pepper leaves. Egg deposition begins within a week after adult moths emerge. Eggs hatch in 4-14 days, depending on temperature. Tiny (1/10 inch long) caterpillars with tan or flesh-colored bodies and black heads begin to disperse along the branches to adjacent plants. European corn borer caterpillars (larvae) always have a black or dark brown head, with a body that is white or gray with a dull pattern. This dark head cap distinguishes them from pepper maggots, which are completely white. A full-grown larva is 3/4 to 1 inch long. After a brief period of leaf feeding, the young larvae migrate to the fruit and enter under the stem cap (calyx). Fruits are not usually attacked until more than 1 inch in diameter. Usually entry holes are marked by an accumulation of brown, sawdust-like excrement at the edge of the calyx. Often this is the only indication that a pepper is infested until two or three weeks after the borer enters, when bacterial soft rot causes the fruit to decay. Once inside, larvae begin to feed on the flesh and seed head contaminating the fruit with their silk, feces and by their presence. It is both difficult and expensive to cull out infested or damaged fruit at the time of harvest.

European corn borer

Larval entry holes also serve as the sight of infection for the soft rot bacteria, Erwinia carotovora, which, although usually present on the fruit surface, requires a wound for invasion. This disease causes a watery decomposition of the flesh, starting at the calyx end. This progresses until the fruit falls from the plant. As the decomposing fruit becomes uninhabitable for the developing caterpillar within, the half-grown larva leaves its home and bores into the side of an adjacent pepper. A single larvae may spread the disease to several fruit, which compounds the losses associated with direct caterpillar feeding. Although crop losses from soft rot may occasionally occur during continuous, hot, humid weather without caterpillar injury, epidemics of this disease in our area usually indicate severe ECB infestations.

In southern New England, there are two generations of ECB each year. The first moth flight usually occurs in June with developing larvae present in late June and early July. This generation is of little economic significance in most pepper plantings, as there are usually no fruit on the plants at that time. Farms located in the warmest New England locations that expect to begin harvest in mid-July, may have to control late-hatching, first generation larvae during cool seasons. This results in delayed egg laying and prolonged larval development. If first generation sprays are needed, the use of selective microbial materials to preserve beneficial insects and maintain control of minor pests may be preferable. The second moth flight starts between mid- July and mid-August, depending upon the year, and varies by as much as three weeks between cool and warm locations in the same season. The larvae of this second moth flight cause substantial crop damage to peppers.

Monitoring and action thresholds

Many IPM growers in southern New England use pheromone traps and action thresholds to monitor ECB moth flights and to delay spraying peppers for as long as possible. If insecticide applications can be delayed until August, beneficial arthropods will usually keep aphids from reaching damaging population levels.
White plastic Scentry Heliothis traps are used to monitor male ECB moths. Traps are placed with the opening and lures at plant height, in the weeds along the borders of pepper fields. These weedy borders are known as active sites, where ECB moths mate prior to moving into the crop to deposit eggs. The traps are emptied and the moths are counted every three to four days, if moth captures indicate that the action threshold may soon be exceeded, or once each week. Trap height and placement are critical for the traps to function properly.

Due to the presence of several different strains of ECB in most locations, it is necessary to use two traps; one baited with the Iowa or Z lure, and the other with the New York or E pheromone blend. The traps should be separated by at least 50 feet. Care should be taken not to cross- contaminate traps because ECB moths attracted to one blend are repelled by the other.

Pheromone lures should be replaced every three to four weeks. To utilize data for action thresholds, combine the moth counts from both traps to calculate moths per week.

The adult male is a brown and tan, night-flying moth less than 3/4 inch long. The most distinguishing feature is a small, light-colored triangular patch with a dark dot in the center, located midway along the front margin of the forewing. Identification is relatively easy because traps baited as instructed capture almost exclusively ECB moths.

The ECB action threshold for peppers is meant to confirm the start of the second generation moth flight. Initiate insecticide applications one week after the combined ECB count in traps equals or exceeds seven moths per week. This threshold allows plenty of time to control the pest and prevent crop damage because there is a two-to-three-week lag between moths captured in traps and fruit infestation by larvae. This relationship and threshold was extensively tested at the University of Connecticut in unsprayed pepper fields and in experiments where plots were treated a week after capturing 7, 14, 21 and 35 moths per week. The seven moths per week threshold has been used successfully in Connecticut’s commercial pepper plantings since 1991.

Creating an action threshold to stop spraying after ECB populations peak and begin to wane has been problematic in New England. Here the first generation is usually not a problem and frost usually occurs before the end of the second moth flight. Still, at some warm sites and in some years, an “inaction threshold” would be nice to have. Field observations on commercial farms indicate that toward the end of each flight, pepper crops are no longer at risk and spraying should stop one week after 21 moths are captured in traps. Perhaps a higher population level can be tolerated toward the end of each generation because egg-laying ceases well before moths die off.

Cultural, natural and biological control

Populations of ECB can be reduced if corn stubble, which provides an excellent site for larvae to survive the winter, is plowed down prior to moth emergence. Early stalk and stubble destruction must be conducted on an area-wide basis to significantly lower the population.

Several species of lady beetles and the insidious flower bug feed on ECB eggs producing from 15 to 50% mortality. Stink bugs, damsel bugs, spiders, and hover fly larvae feed on young caterpillars. An imported parasitic wasp, Macrocentrus grandii (ichneumonidae) may kill up to 18% of the ECB larvae in southern New England. Two naturally-occurring tachinid flies are widespread but contribute little to the overall control of this pest. Researchers have demonstrated that, with periodic mass releases, ECB egg parasitism can be as high as 35% (on corn) using Trichogramma ostriniae and 80% (in peppers) with T. nubilale. The naturally-occurring microsporidian pathogen, Nosema pyrausta, substantially reduces borer populations on corn in some years, but is not considered infectious enough to be used as a biological pesticide.

Management with Insecticides

Once spraying begins, the choice of insecticide can determine the degree of control achieved, the frequency of repeat applications and even the harvest schedule due to label restrictions. It is critical to keep all pepper plants with susceptible fruit protected while ECB moth populations are high. That means that it is important not to exceed the effective residual period (longevity) of an insecticide before making the next application. Many chemical labels require that the last application be made three to seven days prior to harvesting the crop. This restriction can present a problem when trying to meet market orders and for U-pick operations unless pest control and harvest activities are carefully scheduled. You may want to make two identical plantings containing the same pepper varieties so that half the crop is available for harvest when the other has just been sprayed.

The acephate (Orthene) label has a seven day-to-harvest (DH) restriction and calls for repeat applications every seven to ten days. Research results in the literature indicate that this product will often provide effective control of ECB (<1% infestation) on peppers for a much longer period except under extreme (peak) pest pressure. Acephate can be used on bell or non-bell type peppers. Permethrin (Pounce or Ambush, etc.) has a 3-DH restriction, and should be applied every five to ten days. The shorter intervals of five to seven days should be used during summer heat waves and when borer egg hatches are peaking (one to two weeks after peak moth flight). Permethrin is registered for bell peppers only. Asana (esfenvalerate) provides similar control on all pepper types but has a 7-DH restriction and requires almost immediate re application.

The better management approach is to alternate between Coragen (chlorantraniliprole), Intrepid (methoxyfenozide) and Radiant (spinetoram). All three have a 1-DH interval and provide very good control.

Products that contain Bacillus thuringiensis (BT) with formulations that provide some protection from UV light, and thus extended periods of longevity (possibly Agree), may provide acceptable control if applied every three to four days. Although pricey, BT applications are highly preferable to extensive crop damage in specific situations, such as on organic farms, applications at the end of the first generation moth flight, and when there is insufficient time to use a chemical before harvest. Peppers can be harvested just four hours after applying a BT product.

For an updated list of labeled materials for ECB control on peppers, refer to the latest issue of the New England Vegetable Management Guide.

By: Jude Boucher, Vegetable Crops IPM Program Coordinator, University of Connecticut Cooperative Extension System. Updated 2012.

This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.