Zonosemata electa
Pepper maggot is a fly pest that is closely related to apple maggot and has one generation per year. The larvae feed only on solanaceous plants, including ground cherry, horse nettle, tomato, pepper, and eggplant. Pepper is the preferred host, and cherry, bull's horn, and green bell peppers are especially susceptible. Because flies lay eggs directly into pepper fruit, the damage often goes unseen until it is too late. The pepper maggot fly is found throughout eastern North America but is most common along the east coast. Activity of this pest is very localized and varies by farm, region, and year. Many farms never have a problem with this pest and generally do not need to be concerned. Other farms may have it without realizing, because it is possible to confuse maggot damage with damage caused by ECB. The best way to detect activity early on is to look for stings on the fruit, and these are easiest to spot on cherry peppers.
Life Cycle & Identification:
The pest overwinters as pupae in the soil where last year’s host plants were. Adult pepper maggot flies emerge from pupae in mid-July and aggregate in forested field edges to mate, then enter the field during the day to lay their eggs. They are bright yellow and smaller than a house fly, with three yellow stripes on the thorax, green eyes, and clear wings with a distinct banding pattern. Females insert eggs directly into immature pepper fruit, leaving a small dimple called an oviposition sting or scar. Eggs are light-colored and about 2 mm in length, making them difficult to find inside of fruit. There may be several oviposition scars on a single fruit.
After about 10 days, white maggots hatch from these eggs and begin feeding by tunneling within the fruit, especially in the placenta (the spongy white tissue inside the pepper that the seeds are attached to). Maggots grow to about ½ inch in length over a period of about two weeks. They do not have a distinct head capsule, unlike ECB larvae which have brown head capsules. When pepper maggots are ready to pupate, usually in late August or early September, they exit the fruit at the blossom end, leaving tiny round exit holes. Sometimes, the oval-shaped brown pupae can be found inside the fruit. The fly pupates in the soil, overwintering as a pupa before emerging as an adult in the same field the following spring.
Damage:
The presence of oviposition scars and eggs in pepper fruits alone is generally benign and frequently goes unnoticed. However, if left to hatch, the presence of larvae can make fruits unmarketable and their tunneling results in soft spots on fruit walls and brown mines within. Larval exit holes also allow for the entry of soft rot bacteria into the fruit. Damage is often only detected because of premature ripening or decay of the fruit, or fruit filling with water via the exit holes during washing or hydrocooling. If untreated, large pepper maggot populations which have built up for several years can result in infestation rates approaching 100% of their preferred pepper varieties.
Monitoring & Thresholds:
Capturing pepper maggot flies is an effective but largely impractical method of detection, requiring yellow sticky traps be baited with a vial of 28% ammonium hydroxide and placed 20 feet up in maple trees along hedgerows. A simpler way to monitor for fly activity is by scouting their preferred crops for oviposition scars: the marks left by females when laying eggs. The flies prefer to lay eggs in the small (1-3 cm in diameter) round fruit of cherry peppers, and when planted in border rows around a pepper crop, these work very well as indicator plants. If cherry peppers are not part of your crop mix, look for stings on bell or bull's horn peppers, which they also prefer.
If this pest is a concern for your farm, consider using perimeter trap cropping. Plant one row of cherry peppers around the perimeter of the crop. These peppers are more attractive to the maggot flies than the sweet bells, so the flies will build up in the perimeter, allowing for a perimeter spray that will reduce pest populations and protect the main crop. Perimeter trap crop systems can be as effective as whole field sprays while drastically reducing pesticide costs.
Cultural Control:
Since pepper maggot builds up on particular farms or fields rather than spreading out far and wide, you can make an impact on the population size on your farm over time by using cultural practices.
- Disc and plow pepper residue as soon as harvest is complete to kill larvae and pupae.
- Rotate peppers far from last year’s crop.
- Control solanaceous weeds, especially horsenettle.
- Cover the pepper crop with insect netting during egg-laying (beginning in mid-July).
- Remove infested and/or rotting fruit from field at each harvest and destroy (e.g. by feeding to pigs or chickens or burying deeply in a compost or cull pile). This will remove larvae and pupae from the field too.
- Use plastic mulch and/or weedmat as a barrier to prevent larvae from reaching the soil to pupate. Instead, they will get cooked on the mulch or mat surface.
Chemical Control:
Chemical management is generally unnecessary for farms that have never had a problem with pepper maggot. However, the range of this pest seems to be expanding, and scouting for oviposition scars can reveal infestations before they can no longer be controlled. Chemical controls must target the adult fly because eggs and larvae are protected inside the fruit. For farms with a history of pepper maggot activity, it is recommended that an insecticide be applied as soon as adult flies are captured in sticky traps or stings are observed on fruit. Make 2-3 insecticide applications, 10-14 days apart, with a material labeled for pepper maggot.
When the activity of ECB and pepper maggot fly overlap, use of Orthene at 8- to 10-day intervals for control of ECB will also provide control of pepper maggots. However, other selective insecticides for ECB will not control pepper maggot. Conventional insecticides labeled for pepper maggot fly include alpha-cypermethrin, dimethoate, malathion, and zeta-cypermethrin (e.g. Mustang).
For organic production, GF-120 Naturalyte may be used. Spinosad, the active ingredient in both GF-120 Naturalyte and Entrust, must be consumed to be effective. GF-120 Naturalyte contains a bait that entices the flies to lap up the material from the surface of the fruit and therefore consume the insecticide. Entrust does not contain the bait and is therefore ineffective against pepper maggot. When using GF-120 Naturalyte, a large spray droplet size of 4-6 mm is recommended to optimize the duration of this bait’s attractiveness to the flies. See the Pepper Insect Management section of the New England Vegetable Management Guide for more details on using these products.
For more details and up-to-date information regarding pepper maggot control, see the Pepper Insect Management section of the New England Vegetable Management Guide.