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Pests in Gardens and Landscapes: Quick Tips

Sweetpotato whitefly and nymphs.

Examine empty nymphal cases for signs of parasitization. The T-shaped hole in the nymph (above) indicates a healthy adult whitefly emerged whereas an adult parasite emerged from the round hole (below).

A sticky barrier can keep ants out of plants.

Whiteflies are tiny, sap-sucking insects that fly around plants when disturbed. Adults are white and may have darker markings on their wings, while nymphs (immature stage) are oval, legless, and don't move. Nymphs cause most of the damage. Several whitefly species occur in California. Predators and parasites often keep them under control. Prevent whitefly problems by reducing dusty conditions, choosing less susceptible plants, using reflective mulches, and avoiding pesticides that kill whitefly natural enemies. When management is needed, consider using sticky traps, spraying insecticidal soaps or oils, or removing infested plants.

Signs of a whitefly infestation:

• Tiny nymphs on the underside of leaves
• Sticky honeydew on leaves, fruit, or beneath plants, or a covering of black sooty mold
• Yellowing, silvering, or drying leaves that have whitefly nymphs on them
• Deposits of white wax with certain whitefly species

Reduce whiteflies using traps or hand removal.

• Inspect new plants for whiteflies before bringing them into your garden.
• Prune out isolated infested leaves when you first detect them.
• Hose adults off plants with a strong stream of water.
• Hang sticky-coated yellow traps. Use one trap for every medium-size vegetable plant.
• Promptly destroy infested annuals when the flowering or fruiting period ends.

Use reflective mulch to protect young plants.

• Use shiny metallic-coated construction paper or reflective plastic mulch products. These mulches repel whiteflies while plants are small.
• Lay the product on bare soil, bury its edges with soil, and insert seedlings or seeds into holes in the mulch.
• Plastic mulches require drip irrigation underneath them; paper mulches may be sprinkle or furrow irrigated.
• Remove mulches when plants get large and temperatures get hot.

Protect other insects that help reduce whitefly numbers.

• Many beneficials or “natural enemies” such as lacewings and lady beetles help control whiteflies.
• Look for signs of parasitization by mini-wasps, such as circular holes in nymphs or a change in color.
• Prevent dusty conditions since dust can kill or disrupt the activity of beneficials.
• Keep ants out of plants since they protect whiteflies from natural enemies. Don't use pesticides if natural enemies are present.

What about pesticides?

• Choose products that are least harmful to natural enemies—such as insecticidal soaps and oils—and combine their use with the other practices listed above.
• Good coverage, including the underside of leaves, is essential. Repeat applications might be required.
• Avoid using broad spectrum pesticides such as pyrethroids, organophosphates, or neonicotinoids. Even the most toxic insecticides are only partially effective against whiteflies.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.