Vegetable Notes 2025 Vol. 37:13

Management

The impacts of these bacterial and fungal diseases can all be reduced through field sanitation and use of preventative pesticides, whether conventional or organic. 

• Start with quality seed, and/or fungicide treated seed. If saving your own seed, avoid collecting seed from fruit with any defects.

• Resistant or tolerant varieties of many cucurbit crops are available for most of these diseases. Meg McGrath of Cornell University has compiled extensive lists of disease-resistant varieties of vegetable crops.

• Use a 2-year rotation for cucurbit fields. All of these diseases survive on crop residue in the soil, which can persist for up to 2 years.

• Use drip irrigation to reduce the spread of bacteria and fungal spores by overhead irrigation.

• Don’t work in affected fields when foliage is wet, or work in unaffected sections first and infected sections last to avoid spreading disease to unaffected areas.

• Use fungicides or bactericides when you see the first leaf spots to slow the spread of disease. Submit a sample to the UMass Plant Diagnostic Lab so that you can choose an effective pesticide for the disease you have. Consult the cucumber, muskmelon, and watermelon or pumpkin, squash, and gourds disease sections of the New England Vegetable Management Guide for pesticide recommendations.

• Till under crop residues promptly after harvest is complete to encourage the quick breakdown of infected tissues.

--Written by Susan B. Scheufele, UMass Extension

Pepper Maggot & European Corn Borer in Peppers

We are rapidly approaching harvest in pepper fields, and while we can expect there to be some amount of rotting peppers in every field, understanding the source of the damage is key to controlling it. There are diseases that can cause pepper fruit rots, but there are also two insect pests that feed within pepper fruit and cause damage that leads to fruit rots. If you’re culling lots of pepper fruit in the field, we recommend cutting open those fruit to look for pepper maggot and/or European corn borer larvae. This article provides information about how to distinguish between these two pests and control them.

Pepper Maggot

Pepper maggot (Zonosemata electa) adults emerge in mid- to late July and are active for several weeks, laying eggs in the fruit of solanaceous plants where the resulting larvae feed. Affected plants include ground cherry, horse nettle, tomato, pepper, and eggplant, but pepper is the preferred host, and green bell peppers and cherry peppers are especially susceptible.

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 and not realize it, because it is possible to confuse maggot damage with damage caused by European corn borer. Additionally, the range of this pest seems to be expanding. The best way to detect activity early is to look for stings on the fruit, which are easiest to spot on cherry peppers. 

Scouting

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 egg-laying females. 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 peppers—these are their second favorite type of pepper. 

Cultural Practices

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 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. 

European Corn Borer

European corn borer (ECB) is a resident pest that has 2 generations per year in southern and central New England and 1 generation in northern New England. This pest prefers sweet corn but can cause damage in a wide range of crops, including bean, potato, garlic, and pepper. ECB generally does not become a pest in peppers until the appearance of the second generation in late July or early August (1400 GDD base 50°F). Most locations in MA are past or almost at 1400 GDDs (see Table 2 in Pest Alerts). The severity of ECB damage in peppers varies throughout the state. Some farms—typically in areas where farming is less dense and ECB populations have not built up— do not see much damage from this pest. In the Connecticut River Valley and in southeastern MA, an unsprayed pepper field can have anywhere from 10 to 100% of the fruit infested. In some cases, it seems that sweet corn—which ECB prefer over peppers—helps to draw ECB away; in other cases, presence of sweet corn near peppers provides no benefit at all. 

Life Cycle and Damage

ECB larvae overwinter in stalks of corn and other host plants and pupate in the spring. Adult moths emerge in late May or early June and mate in weedy or grassy areas. The moths are about ¾” long and light brown in color with lighter bands on the wings. Females lay masses of flat, white eggs 3 to 7 days after they emerge (depending on temperature). Eggs hatch in about 5 to 7 days (100 GDDs base 50°F). After the eggs hatch, the newly emerged larvae feed on leaf tissue for a short period and then bore into stems or fruit. ECB larvae often burrow into the fruit beneath the calyx. In addition to this direct injury, ECB damage also causes premature fruit ripening. Boring holes also allow for the entry of pathogens into the fruit, which can cause fruit rot. Controlling ECB larvae before they reach the pepper fruit is essential for effectively managing this pest. Larvae vary in color from light-gray to pink but always have small, dark spots on each body segment and brown head capsules.

Thresholds and Chemical Control

ECB emergence is monitored using pheromone traps that attract male moths. Traps at sites across the state are checked weekly and moth counts are reported in the sweet corn section of Pest Alerts. New York and Maine also publish weekly trap counts. Historically, our recommendation was to time spray applications based on trap counts. Those recommendations were to make the first application in fruiting peppers 1 week after 7+ moths per week were trapped, and discontinue sprays 1 week after moth counts dropped below 21 moths per week, using shorter spray intervals during peak flights and when trap captures exceed 150 moths per trap weekly. ECB trap counts in sweet corn have been mysteriously very low over the last several years, despite the presence of larvae in sweet corn crops, so these spray thresholds may not be practical anymore. If you struggle with ECB in your peppers, pheromone trapping in your pepper fields may still be useful to indicate the presence of ECB and alert you to when sprays may be warranted. Choose selective/microbial products such as Bacillus thuringiensis aizawai or kurstaki strains whenever possible to preserve beneficials and reduce the chance of aphid outbreaks, which can be caused when pyrethroids are used and natural enemies are killed. For other chemical control options see the pepper insect section of the New England Vegetable Management Guide.

Biological Control

ECB can also be controlled using the parasitic wasp, Trichogramma ostriniae. ECB will invade pepper fruits that are > ½ inch across, and T. ostriniae attacks only the egg stage of ECB, so timing is critical. We recommend that you begin releases the week that flight begins and continue weekly releases for a total of 4 weeks. Release 90,000 to 120,000 wasps per acre and spread the cards out throughout your pepper block. Higher rates are needed in peppers compared to sweet corn because the tolerance for damage is virtually zero and ECB larvae attack the fruit directly. Four releases are needed because the egg-laying period for the second generation is longer than for the first generation of ECB. Fortunately, peppers are also a higher value crop and worth the extra cost. After four releases, Trichogramma will have reproduced in the field and will continue working to control ECB. It may be too late to order wasps for this year, but you can plan ahead for next year. Wasps can also be used in combination with insecticides, but choose a selective material (see above) that will not kill wasps.

--Written by UMass Vegetable Program

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Vegetable Notes. Maria Gannett, Genevieve Higgins, Lisa McKeag, Susan Scheufele, Alireza Shokoohi, and Hannah Whitehead, co-editors. All photos in this publication are credited to the UMass Extension Vegetable Program unless otherwise noted.

Where trade names or commercial products are used, no company or product endorsement is implied or intended. Always read the label before using any pesticide. The label is the legal document for product use. Disregard any information in this newsletter if it is in conflict with the label.

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