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).
Whiteflies are tiny, sap-sucking insects that damage leaves of many plants. Adults are white and sometimes have darker markings on their wings. Nymphs, which cause most of the damage, are oval, legless, and don't move. Many species occur in California landscapes, and natural enemies keep most under good control. Prevent whitefly problems by using reflective mulches, avoiding dust, choosing less susceptible plants, and eliminating pesticides that kill whitefly natural enemies. When management is required, consider using sticky traps, insecticidal soaps or oils, or removing infested plants.
Signs of a whitefly infestation can include:
- 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 whiteflies.
Protect natural enemies such as lacewings, lady beetles, and mini-wasps.
- Avoid using pesticides such as pyrethroids, organophosphates, carbaryl, or imidacloprid.
- Prevent dusty conditions.
- Keep ants, which protect whiteflies from natural enemies, out of plants.
- Recognize signs of parasitization such as circular holes in nymphs (see photos) or a change in color.
Install a reflective mulch in your vegetable garden to protect young plants.
- Use shiny metallic-coated construction paper or reflective plastic mulch products.
- Lay the product on bare soil, bury its edges with soil, and insert seedlings or seeds into holes that you make in the mulch.
- Plastic mulches require drip irrigation underneath them; paper mulches may be sprinkle or furrow irrigated.
- Mulches repel whiteflies and other small flying insects such as aphids while plants are small. Remove mulches when plants get large and temperatures get hot.
Use hand removal and traps to reduce whiteflies.
- 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.
- Install ready-to-use, sticky-coated yellow traps or make your own. Use one trap for every medium-size vegetable plant.
- Promptly destroy infested annuals when flowering or fruiting ends.
Even the most toxic insecticides are only partially effective. If you decide to treat, choose products that are least harmful to natural enemies—such as insecticidal soaps and oils, including neem oil—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 even these pesticides if many natural enemies are present.
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.