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Pests in Gardens and Landscapes: Quick Tips

Adult western flower thrips.

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

Leaf bleaching and black speckling caused by thrips.

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 injury from thrips. Manage these insects by combining good cultural care, pest exclusion, thrips-resistant plants, and less toxic insecticides.

Thrips are tiny, slender insects.

• 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.
• 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.
• Certain thrips are beneficial predators of some insects and mites.

Damage often isn’t apparent until tissue grows and expands. Look for:

• 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 acting.

• 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 blue or bright yellow sticky traps to detect flying thrips.

Thrips are difficult to control. Combine methods for best results.

• Find out what species you have and read Pest Notes: Thrips for the best approach.
• Protect parasites and predators of thrips by avoiding persistent pesticides.
• Avoid overwatering or applying nitrogen fertilizer, which can increase thrips populations.
• Prune off declining, injured, or infested plant parts.
• Use row covers or cages over small plants to exclude thrips and other flying insects.
• If plant foliage covers less than half of the soil surface, soil can be covered with reflective mulch to repel flying thrips.

What about pesticides?

• Pesticides won’t restore the appearance of injured plant material. Plants remain damaged until injured tissue drops or is pruned off and new growth appears.
• Often pesticides won’t be effective unless you wait until the next season and spray new plant 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.