How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Several species of whiteflies may infest peppers. Silverleaf whitefly is also known as sweetpotato whitefly B biotype. Proper identification of silverleaf whiteflies and greenhouse whiteflies is important because other whitefly species do not cause economic damage in pepper. Use a hand lens to examine both immatures and adults. Whitefly adults are tiny (0.06 inch, 1.5 mm long), yellowish insects with white wings. Silverleaf whiteflies hold their wings somewhat vertically tilted, or rooflike, over the body; the wings do not meet over the back but have a small space separating them. Greenhouse whitefly adults are very similar in appearance to the silverleaf whitefly but hold their wings flatter over the back and there is no space between the wings where they meet in the center of the back.

Whiteflies are found mostly on the undersides of leaves. They fly readily when plants are disturbed. The tiny, elongated eggs hatch into a first larval stage that has legs and antennae and is mobile. Both legs and antennae are lost after the first molt and subsequent stages remain fixed to the leaf surface. The last nymphal stage, often called the pupa or the red-eye nymph, is the stage that is easiest to identify. Silverleaf whitefly pupae are oval, whitish, and soft. The edge of the pupa tapers down to the leaf surface and has few to no long waxy filaments around the edge. In contrast, greenhouse whitefly pupae have many long waxy filament around the edge and the edge is somewhat vertical where it contacts the leaf surface.

DAMAGE

Whiteflies damage peppers by sucking enormous quantities of sap and covering plants with sticky honeydew. Black sooty mold grows over the honeydew, lowering the photosynthetic capacity of the plant and making the fruit unattractive. Feeding by high populations may result in stunting, poor growth, defoliation, and reduced yields.

MANAGEMENT

Whitefly population are not consistent from year to year, so monitoring is important in detecting and preventing the development of populations in any given year. In addition, an integrated pest management program for whiteflies includes following good cultural practices, such as host-free periods, conserving natural enemies, and using pesticides only when necessary.

Biological Control
Several wasps, including species in the Encarsia and Eretmocerus genera, parasitize whiteflies. Whitefly nymphs are also preyed upon by bigeyed bugs, lacewing larvae, and lady beetle larvae. Silverleaf whitefly is an introduced pest that has escaped its natural enemies. Some indigenous native parasites and predators do attack it, but do not keep it below damaging numbers. The parasitic wasp, Encarsia formosa, has been used successfully to control greenhouse whitefly in greenhouses or protected crop situations elsewhere in the world where peppers are more commonly grown in this manner.

Cultural Control
The best control for silverleaf whiteflies is to maximize the distance and time interval between host crops. When possible, plant peppers at least one-half mile upwind from key silverleaf whitefly hosts such as melons, cole crops, and cotton. Maintain good sanitation in areas of winter/spring host crops and weeds by destroying and removing all crop residues as soon as possible. Control weeds in noncrop areas including head rows and fallow fields and harvest alfalfa on as short a schedule as possible. In addition, allow the maximum time between silverleaf whitefly host crops and produce vegetables and melons in the shortest season possible.

Adult silverleaf whiteflies are repelled by silver- or aluminum-colored mulches. Place reflective polyethylene mulches on planting beds before seeding or transplanting to significantly reduce rate of colonization by whiteflies and delay the buildup of damaging numbers of whiteflies by 4 to 6 weeks. The mulches lose their effectiveness when more than 60% of the surface is covered by foliage. Therefore, they are effective only for the first few weeks after seedling emergence or transplanting.

Greenhouse whiteflies are often induced by applications of broad-spectrum pesticides. Avoid such materials early in the season.

Organically Acceptable Methods
Cultural and biological control as well as sprays of insecticidal soaps and certain oil sprays are acceptable for use on organically certified produce.

Monitoring and Treatment Decisions
Routinely check field margins for whiteflies; these areas are usually infested first. Be especially alert for rapid population build up when nearby host crops are in decline. During these critical periods, check pepper fields twice weekly. Sticky traps may be useful in detecting initial whitefly migrations into fields.

Allow beneficials an opportunity to control light silverleaf whitefly infestations. If higher populations are present at the field margins than the field centers, then treat only the field margins. This approach will reduce treatment costs and help preserve beneficials in the field. The treatment threshold for silverleaf whitefly is about 4 adults per leaf in a random 30-leaf sample of healthy leaves. Thresholds have not yet been established for greenhouse whitefly.

Insecticidal soaps and oils are not as effective as the other materials and require frequent application and good coverage.

PUBLICATION

UC IPM Pest Management Guidelines: Peppers
UC ANR Publication 3460
Insects and Mites
E. T. Natwick, UC Cooperative Extension Imperial County
J. T. Trumble, Entomology, UC Riverside
Acknowledgment for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
R. L. Coviello, UC Cooperative Extension, Fresno County
C. G. Summers, Kearney Agricultural Center, Parlier
W. E. Chaney, UC Cooperative Extension, Monterey County
C. F. Fouche, UC Cooperative Extension, San Joaquin County

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