Pest description and crop damage Adult thrips are small (about 1-2 mm long at maturity), slender insects with fringed wings. They are generally white when young but pale yellow to brown when mature. Larvae are very tiny and difficult to distinguish without magnification. They feed by puncturing plant material, often blossoms, and sucking out the cell contents. Injured blossoms often turn into distorted fruit. When feeding on flowers, affected petals appear stippled or are scarred with brown streaks or spots. When unusually abundant in spring, thrips have been reported to cause blossom blasting. Fruit may be misshapen or distorted. Controls are most effective when applied at flowering; field control is not practical in eliminating thrips present at harvest.
Biology and life history Thrips overwinter as adults in ground duff. In the spring they seek out flowers where they feed on pollen and nectar and lay eggs into floral parts. The larvae feed on flowers, buds and leaves. When mature, the larvae drop to the ground and pupate. The adults that emerge may lay eggs on developing fruit. Under favorable conditions, a complete life cycle may be completed in two weeks. There are several overlapping generations per year. Seasonal migration occurs at various times of the year due to destruction or drying up of host plants; adjacent crops may be invaded by these insects. Thrips eat pollen and nectar on a wide range of plants (at least 244 species from 62 families).
There are no significant natural controls early in the season when damage is occurring. Later in the year, predators such as lacewings and minute pirate bugs may reduce populations. Cold, wet weather during bloom much reduces thrips damage.
Fields adjacent to unmanaged or wild land that contains many flowering host plants are often subject to more damage because of the habitat such areas offer. If other flowering plants with desirable flowers (complex flowers, yellow, white or blue in color) are nearby and in bloom at the same time as strawberries, allowing these to flower may reduce activity in the strawberries.
Management-chemical control: HOME USE
Sprays should be applied before blooms open or after petal fall to avoid bee injury.
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
- pyrethrins (often as a mix with other ingredients)-Some formulations are OMRI-listed for organic use.
- spinosad-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- acetamiprid (Assail) at 0.035 to 0.075 lb ai/a. PHI 1 day. Do not exceed more than two applications per season.
- azadirachtin (Neemix and other brands)-Consult label for rate and use directions. Some formulations are OMRI-listed for organic use.
- Beauveria bassiana (Mycotrol and other brands)-Consult label for rate. Some formulations are OMRI-listed for organic use.
- malathion (several brands) at 1 to 1.88 lb ai/a. PHI 3 days.
- naled (Dibrom) at 0.9 lb ai/a. PHI 1 day. Use in evening after bee activity has ended. Restricted use pesticide.
- spinetoram (Radiant SC) at 0.05 to 0.08 lb ai/a. PHI 1 day. Suppression only; control may be improved with the addition of an adjuvant.
- spinosad (Success or Entrust) at 0.062 to 0.09 lb ai/a. PHI 1 day. Entrust is OMRI-listed for organic use.
- sulfoxaflor (Closer SC) at 0.07 lb ai/a. PHI 1 day. Apply when thrips first appear. Provides suppression only. Do not apply when bees are actively foraging. Note: Strawberry registration was cancelled on Nov. 12,11/12/2015 but EPA ruled that all product still in the hands of growers is allowed to be used until exhausted.