Plum and prune-Thrips


Pear thrips (Taeniothrips inconsequens)

Western flower thrips (Frankliniella occidentalis)

Pest description and crop damage Thrips are minute, slender insects about 1 mm long. Adult thrips are dark brown to black in color with reddish brown eyes. The larvae are white. Most of the feeding damage occurs prior to bloom, when adults feed on the fruit buds. This causes buds to dry up, die, or develop abnormally. Foliage damaged by thrips feeding appears distorted, tattered, or stunted. Fruit damaged by thrips may show surface russeting or discoloration later in the growing season.

Biology and life history Thrips overwinter as pupae in protected places on the ground. In spring, the adults fly to trees and enter developing buds to feed. Eggs are laid in the flower parts and along the mid-vein and petioles of developing leaves. The young larvae emerge to feed on the flower parts and foliage. Several generations pass each summer, and adults may feed on adjacent flowering plants as well.

Pest monitoring Thrips are monitored easily by shaking a pink bud or flower cluster into a white cup. If you find only 25 to 50 thrips per 100 buds when 50% of blossom buds show green, damage will not be too serious. In some cases, sprays for other pests will reduce the thrips population.

Management-biological control

Adults and nymphs of the minute pirate bug (Orius spp.) attack thrips, as do larvae of green lacewings and predaceous thrips. Cold, wet weather during bloom reduces thrips damage.

Management-cultural control

If thrips have been a problem, prune and thin after bloom, as this will dilute the populations of thrips and reduce the damage. Remove as many broadleaf flowering plants as possible from the vicinity of the trees, as this provides an alternate host. Grass groundcovers around the trees provide competition for clovers and winter annuals that are alternate hosts.

Management-chemical control: HOME USE

Warning: Many pesticides are hazardous to bees. Look for bee precautionary statements on product labels and do not use these products during bloom or if bees are foraging in the orchard.

  • acetamiprid-Toxic to bees.
  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • carbaryl-Highly toxic to bees.
  • gamma-cyhalothrin-Highly toxic to bees.
  • horticultural mineral oil-Some formulations OMRI-listed for organic use.
  • imidacloprid-Highly toxic to bees. Soil drenches may have residual activity in woody plants lasting for 12 or more months. If short-term management is the goal, consider other approaches.
  • insecticidal soap-Some formulations are OMRI-listed for organic use.
  • kaolin-Applied as a spray to leaves, stems, and fruit, it acts as a repellant to some insect pests. Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin-Highly toxic to bees.
  • plant-derived essential oils-Some have shown efficacy against thrips. Some formulations are OMRI-listed for organic use.
  • pyrethrins (often as a mix with other ingredients)- Highly toxic to bees. Some formulations are OMRI-listed for organic use.
  • spinosad-Toxic to bees. Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin-Highly toxic to bees.

Management-chemical control: COMMERCIAL USE

Spring and summer spray

  • lambda-cyhalothrin (Warrior II) at 1.28 to 2.56 fl oz/A. REI 24 hr. PHI 14 days. May disrupt beneficial mite populations. Extremely toxic to fish; avoid spray drift and surface runoff.
  • spinetoram (Delegate WG) at 4.5 to 7 oz/A. REI 4 hr. PHI 1 day. Apply no less than one week apart, with a maximum 4 applications per season.
  • spinosad (Entrust SC) at 4 to 8 fl oz/A. REI 4 hr. PHI 1 day. Results are best when applied at petal fall. May act slowly. OMRI-listed for organic use.
  • thiamethoxam+chlorantraniliprole (Voliam Flexi) at 6 to 7 oz/A. Do not apply exceed 14 oz/A of Voliam Flexi per season. REI 12 hr. PHI 14 days.