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Pests in Gardens and Landscapes: Quick Tips

When thrips feed, they distort or scar leaves, flowers, or fruit. Healthy woody plants usually tolerate thrips, although damage can become unattractive. Herbaceous ornamentals and developing fruits and vegetables can suffer more serious injuries. Use an integrated program combining good cultural care, pest exclusion, planting thrips-resistant species, and protecting natural enemies by using least-toxic insecticides.

Adult western flower thrips.

Thrips are tiny, slender insects with hairs on their wing margins.

• They are less than 1⁄20 inch long, and their color varies depending on the species and life stage.
• Thrips hatch from eggs and develop through two feeding larval (nymphal) stages and two nonfeeding stages (prepupa and pupa) before developing into adults.
• Certain thrips are beneficial predators of some insects and mites.
• Most pest thrips feed while hidden, often in buds and shoot tips or beneath sepals; you’ll often observe the damage before seeing the thrips.
• Greenhouse thrips and western flower thrips are two common pest species in landscapes.

Damage often isn‘t apparent until tissue grows and expands. Look for:

Greenhouse thrips adults (black) and nymphs (yellow).

• Scabby, silvery to dark brown discoloration on fruit, leaves, or petals.
• Dark specks of excrement on fruit or leaves.
• Distorted, curled, galled, or dead shoot tips and leaves.

Check for thrips before you treat!

Be certain that pest thrips are present and causing damage before taking control action. Harsh weather, inadequate plant care, pathogens, and other invertebrates can cause similar-looking damage. Shake foliage or flowers over white paper to see if this dislodges any thrips. Hang bright yellow sticky traps to detect flying thrips.

Thrips are difficult to control. Combine methods in an IPM program:

Leaf bleaching and black speckling caused by thrips.

• Find out what species you have and research the best approach; see Pest Notes: Thrips.
• Conserve parasites and predators by avoiding persistent pesticides.
• Avoid overwatering or applying nitrogen fertilizer, which can increase thrips populations.
• Prune off declining, injured, or infested plant parts.
• Apply row covers or cages over small plants to exclude thrips.
• Cover soil with reflective mulch, which repels flying thrips if foliage covers less than about half of the soil surface.

Pesticides.

Pesticides won’t restore the appearance of injured tissue. Plants remain damaged until injured tissue drops or is pruned off and new growth appears. Thrips are difficult to control with pesticides. Often pesticides won’t be effective unless you wait until the next season and spray new growth.

Horticultural oils, insecticidal soaps, and pyrethrins can provide temporary control, especially for greenhouse thrips. Spinosad may be more effective. Pesticides alone rarely provide good control, so combine spraying with other methods.

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.