Pepper Maggot: Damage, Detection, Monitoring, and Management

If there are maggots in your peppers, and nobody knows it, do you still have a pest problem?

The pepper maggot can damage peppers and eggplant in southern New England. If harvested green, peppers may be sold with unhatched eggs or young larvae (maggots) within. Usually, this type of infestation is undetected by unsuspecting wholesale buyers or even consumers, who may not notice the tiny maggots in the discarded seedhead. Occasionally, larvae tunnel in the flesh of the pepper, just under the skin, leaving an opaque scar on the sidewall, which is visible from the exterior and is easily culled during picking or packing operations. If the maggots are allowed to mature, the seedhead becomes riddled and discolored due to their feeding. As the full grown maggots leave the fruit to pupate in the soil, exit wounds become contaminated with soft rot bacteria, causing extra-large greener mature (i.e., red) fruit to melt into a watery-rot during late August or early September. The soft rot may be mistaken for the root of the problem causing the grower to make unnecessary and ineffective fungicide or copper applications. Larger maggots may be detected by customers or may contaminate processed fruit and food products made with the peppers. Pizzerias have been known to fail health inspections due to the presence of maggots on their pizzas! Do you have a pest problem if there are maggots in your peppers…. ask the health inspector, the processor’s USDA inspector, the processor, the owner of the pizzeria or the person who ate the pizza.

Infestations by the pepper maggot are patchy and sporadic. Even on farms with a history of this pest, fruit may be infested only on one side of a large field, or in one or two pepper fields on a farm (but not all fields), or not at all in a given year. On the other hand, 100% of the fruit on a farm can be infested when fly populations are high. In the three southern New England states, any new field you rotate your peppers or eggplant to has the potential to be infested. Also, the adult fly has been known to migrate up to a half mile to infest fields with no previous history of this pest.

Control options need to target the adult fly because eggs are deposited under the skin of the fruit and are hard to kill, as are the maggots which reside inside the pepper. Pepper maggot flies emerge from the soil for 10-14 days between mid-July and early August. Emergence time may vary by two or more weeks due to temperature variations between years. Egg laying begins approximately one week after the flies emerge and maggots mature about a month later. So how do you decide if insecticide applications are necessary for this pest and when to spray your crop? The key is to learn how to detect pepper maggots through trapping or scouting.

pepper maggot

The fly is easy to recognize once you are taught how. The pepper maggot fly has three bright yellow strips down its back (thorax) and banded wings, with a distinct pattern. Some of my research over the past seven years has been aimed at developing a reliable monitoring or trapping system for this fly. After attempting to capture the fly, with over two dozen different types of trap/bait combinations, in many different positions around the field, we finally succeeded. What took us so long? There are a number of complicating factors that led to our slow progress.

The flies do not seem to respond to traps placed in the crop, despite the fact that they can be observed mating on pepper plants and/or depositing eggs in the fruit close to traps. The flies can sometimes be detected with traps hung low (3-7 feet high) along hedgerows or tree-lines that border host crops. However, this is not always reliable either, and if successful, will result in the capture of a very low number of flies. In 1996 and 1997 we attempted to trap flies at varying heights in the canopy of several common species of trees that exist along the borders of New England pepper fields. We found that the flies respond much better to traps placed at a height of between 20-28 feet, than to lower positions. We also found that we could capture four to fourteen times as many flies in sugar maple trees compared with choke cherry, black cherry, pin oaks and white pines.

The most successful trap/bait combination attempted to date, is a modified version of the Still’s-style trap used for apple maggot and other fruit fly pests in Ohio over 35 years ago. This system utilizes a rectangular, yellow, sticky-trap (available commercially as an AM Trap) baited with a vial of 27-31% liquid ammonia. We now have a very high degree of confidence that by placing the Still’s-style trap at the 20 foot height in sugar maple trees along the margins of pepper fields, one can reliably capture pepper maggot flies, if present.

However, there may be a much simpler and more practical way to determine if and when to spray. In 1997, each pepper field with a history of pepper maggot damage was surrounded with hot-cherry pepper plants spaced at 25, 50 and 100 meters apart, depending upon the size of the field. All the hot pepper plants were located in the outer-most row of bell peppers along the margins of the fields. Still’s-style traps in trees were also employed at almost every site. The idea was to utilize the early-set and high attraction of the chili peppers as indicator plants to detect the start of egg laying. We then proceeded to check for oviposition scars or (egg deposit) stings on the hot-cherry fruit on the indicator plants and the traps every three to four days. Stings are easily recognized on the high-gloss, smooth surface of a cherry pepper as a shallow indentation of the fruit surface with a tiny scar in the center. In every case, the flies appeared on the traps at the same time that the first few stings appeared on the hot-cherry peppers. Both the number of flies captured and the number of fruit stings increased over time. By timing insecticide applications with the first occurrence of the stings on the indicator plant’s fruit, damage to the main crop can be avoided with a minimum of spraying.

Why not just spray all pepper fields after fruit set and to hell with scouting and monitoring? All of the broad-spectrum chemical insecticides registered for pepper maggots also kill off the predator and parasites that very effectively control aphids on peppers. The later you wait into the season to make your first insecticide application, the less likely your pepper field is to develop high aphid populations. In short, growers who have to battle pepper maggots often have to also fight aphids late in the season; those that don’t have to spray for the fly, almost never have a problem with aphids.

So what works and what doesn’t? In an attempt to find some alternative to harsh broad-spectrum insecticides, we conducted an efficacy trial on the botanical azadirachtin (originally derived from neem trees in India) in the product Neemix. Early studies of this chemical on other crops indicated that it had some degree of repellence on other fruit flies (i.e. apple maggot) and may not disrupt beneficial insect populations. We planted 600 pepper plants at three farms where pepper maggots have been a chronic problem. Half of each planting was treated with a full rate of Neemix each week, for seven weeks, starting when the first pepper maggot fly was captured. The other half of the planting was left as an untreated check (control) plot. Beneficial insects and spiders were counted on the leaves of 30 plants from each plot before, during and after spraying.

In late August, when pepper maggot (larvae) were nearing maturity, the commercial-size peppers from 30 plants per plot were harvested. Pepper maggot stings and larvae were counted on or in each fruit. European corn borer larvae were also counted. Unfortunately, there were no significant differences between pest or beneficial populations for either treatment. In fact, on 1 August numerous pepper maggot flies were observed on the plants and fruit of both treatments after several applications of Neemix had been applied to half the planting.

In commercial fields, sprays should be targeted at the adult fly as soon as it is detected on traps or with indicator plants. During warm temperatures (90 degrees F) flies emerge within 10 days and can be controlled with 1-2 well timed sprays, five to eight days apart. In cooler seasons and when using materials with shorter residual periods of effectiveness, three applications may be necessary to control the fly.

Dimethoate (e.g. DiMate, 0 dh), malathion (e.g. Malathion 8E, 3 dh) and endosulfan (e.g. Thiodan, l2 dh) are all registered for pepper maggots on peppers. Endosulfan is also registered for eggplant, but is restricted to two applications per season on both crops. In Connecticut, endosulfan resistance may be a problem on some farms, as even well- timed sprays often provide little or no control. Dimethoate and malathion usually provide excellent control of this pest, although my experience with the latter is limited. Since these trials were done, two new materials have received registration for pepper maggot: Spinosad (GF-120 Naturalyte) and zeta-cypermethrin (Mustang). Acephate (e.g. Orthene 7dh) is registered on peppers to control European corn borer and aphids but not pepper maggots. In fields where acephate has been applied with the correct timing for pepper maggot, it usually provides excellent control, but not always. Dimethoate and acephate are systemic materials and have a relatively long residual period while malathion and endosulfan are stomach and contact poisons only, with much shorter periods of activity. Other commonly used pepper insecticides such as Pounce, Ambush, Lannate, and Bacillus thuringiensis products are not registered for pepper maggot control and will not provide protection from this pest.

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.

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