Pepper IPM: Aphids

Description, Damage and Management

Aphids are tiny (less than 1/8 of an inch), soft-bodied, pear-shaped insects that inhabit the underside of leaves and suck out plant juices with piercing-sucking style mouthparts. There are two species that may damage peppers in New England; the green peach aphids (GPA) and the melon aphid (MA). The GPA is by far most common species found on peppers. MA colonizes peppers far less frequently but may become the dominant population in some years. GPA are slightly larger and are usually yellow or light-green but may on occasion be pink in color. MA range in color from light to dark-green or black, with black leg joints and rear-facing projections called cornicals (which resemble a car’s tailpipe). GPA do not have black cornicals.

Fortunately, pepper plants can tolerate populations of aphids without sustaining any direct damage from the feeding itself. GPA and MA are capable of spreading certain viruses to peppers. If populations get too high, aphids may produce cosmetic damage by excreting sticky honeydew (sugary plant sap) which allows sooty mold fungus to grow on fruit. At even higher populations, aphid colonies can consume so much plant fluid that leaf curling or distortion may occur.

In New England, the GPA is easily controlled by beneficial insects and other natural control agents throughout most of the season. Beneficials include both the immature and adult stages of various lady beetles species, minute pirate and damsel bugs, predacious midge, flower fly and lacewing larvae, several species of parasitic wasps, spiders and fungal pathogens. Applications of broad-spectrum insecticides kill many of these beneficials and allow aphid populations to increase rapidly.

Aphids have tremendous reproductive capabilities and can quickly build to damaging levels if their populations are not contained by naturally occurring parasites and predators or other factors. Aphids have the ability to skip the mating and egg-laying process and give birth to live young; usually wingless females. Under warm conditions, each aphid can produce 80 or more young females in a week. Many generations occur in a single season. Once the beneficial insect complex is killed off, there is little change that they will regain control over the rapidly expanding aphid population. To further complicate the problem, both the GPA and MA are resistant to most insecticides. When applied, aphicides usually result in less than adequate control, allow the aphid populations to continue to increase, and result in even more spraying. It is therefore essential to minimize early-season insecticide applications by ignoring the limited plant injury caused by most minor pests, spot-treating or using selective microbial products if necessary, and delaying broad-spectrum sprays for major pests as long as possible through the use of monitoring techniques and action thresholds. This strategy allows the beneficial insects to keep the aphids in check through most of the season until it is too late for them to cause significant economic damage.

Does this strategy work? When pepper transplants come out of the greenhouse with as many as 50 GPA per leaf, if left unsprayed, beneficials in the field reduced the population to less than one aphid per leaf in as little as one or two weeks. In six years of monitoring aphid populations on a weekly basis on commercial pepper farms in Connecticut, IPM fields have never required a single spray to control GPA unless they had a previous broad-spectrum insecticide application. In 1993, MA populations increased to unacceptable levels on both sprayed and unsprayed pepper plantings across the state. Fields that were sprayed repeatedly with an insecticide or even a combination of aphicides, generally, had higher aphid populations, later into the season, than untreated fields.

Monitoring aphid populations

In the Connecticut Pepper IPM Program field scouting begins in June and continues on a weekly basis into September. Growers check for aphids on the underside of two lower and two upper leaves on each of 25 plants chosen at random as they walk through their pepper planting. The average number of aphids per leaf is determined. The approximate ration of GPA to MA is important if it becomes necessary to select an insecticide. By quantifying the population and recording the data each week it is easy to see if populations are increasing, decreasing or relatively stable over time. Growers also learn to identify important predators and parasites during this process and begin to realize how plentiful beneficials really are.

Action Threshold and Chemical Control

If aphid populations exceed 10 per leaf before fruit set and 5 per leaf after fruit set, deposits of honeydew will start to accumulate on the plants and fruit. Insecticide applications should begin if populations remain between eight and 10 aphids per leaf for two consecutive weeks. Acephate (Orthene) and dimethoate (Dimate) are among the more effective materials for GPA, while imidacloprid (Provado), or methymul (Lannate) may be more effective for MA control. Always alternate between chemical families when spraying to avoid selecting for the survival of resistant individuals. Continuous preventive use of aphicides will eventually result in resistant populations.

For more information on chemical controls, consult the latest New England Vegetable Management Guide

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

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