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 ECB moths deposit batches of five to 30 eggs on the underside of pepper leaves. Eggs hatch in one to two weeks, depending upon temperatures. Tiny (1/10 inch long) caterpillars with tan or flesh-colored bodies and black heads begin to disperse along the branches to adjacent plants. After a brief period of leaf feeding, the young larvae migrate to the fruit and enter under the stem cap (calyx). Usually entry holes are marked by an accumulation of brown, sawdust-like excrement at the edge of the calyx. Fruits are not usually attacked until more than 1 inch in diameter. Once inside, larvae begin to feed on the flesh and seed head contaminating the fruit with their silk, feces and by their presence.
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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.
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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.
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.
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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.
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.
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.
Products that contain Bacillus thuringiensis (BT) with formulations that provide some protection from UV light, and thus extended periods of longevity (MVP and possibly Agree), may provide acceptable control if applied every three to four days. In a test at the University of Connecticut, under moderate ECB pressure, MVP applied twice a week provided similar control (3% infestation) as Ambush used weekly. 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.
Sevin (carbaryl) can be used just 12 hours prior to harvest. Although it will lower borer numbers, carbaryl does not provide satisfactory control for most commercial growers. In addition, applications may lead to high aphid populations. Avoid the common mistake of using Lannate (methomyl) to control ECB on peppers. This pest/crop combination is not on the Lannate label. Methomyl will not perform as well as other products due to a very short residual period. There are several other chemical options available.
The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. 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.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.