Agriculture: Strawberry Pest Management Guidelines

Western Flower Thrips

Frankliniella occidentalis

Description of the Pest

Western flower thrips are slender, about 0.03 inch (0.8 mm) long insects when mature. Adults have feathery wings and vary from yellow to dark brown. Nymphs are white or yellowish with small dark eyes. In spring, there is an increase in the number of flower thrips on alfalfa, weeds, ice plant, and other vegetation and move from these hosts when they are cut, stop flowering, or dry up.

Strawberry plantations often have a mixed population of thrips that includes a low percentage of the onion thrips, Thrips tabaci.

Damage

Thrips feeding on strawberry blossoms cause the stigmas and anthers to turn brown and wither prematurely, but not before fertilization has occurred. Although often numerous on berries when cat-facing occurs, western flower thrips do not cause cat-facing, which is a result of lygus bug feeding and possibly other factors. As fruit develops, thrips feeding may cause a russeting (Type I bronzing) of the fruit around the cap, but this injury is seldom economic. (Other types of bronzing are associated with phytotoxicity from sulfur and other types of sprays (Type II) and from plant physiological factors (Type III). The most severe bronzing that covers the entire fruit is believed to have a physiological cause that is associated with hot temperatures occurring from May through July.

Management

Western flower thrips thrive and increase their numbers on many crops and weeds. They may migrate into strawberries when other crops are harvested, when second-year strawberries or other perennial hosts stop flowering, or when weeds dry up in spring. Control is usually not necessary because western flower thrips rarely cause economic damage at densities that typically occur in strawberry fields. Sprays applied to control thrips disrupt biological control of other pests such as twospotted spider mites, lygus bugs, whiteflies, and other insects. If an insecticide is necessary, choose the least disruptive insecticide to preserve biological controls agents.

Biological Control

Naturally occurring minute pirate bugs (Orius spp.) feed on thrips. Orius are also available commercially, but release rates and timing have not been determined.

Organically Acceptable Methods

Use sprays of the Entrust formulation of spinosad, azadirachtin (Neemix), Isaria fumosorosea (PFR-97), Beauveria bassiana (Botanigard), or combinations of these products on organically certified strawberries.

Monitoring and Treatment Decisions

Consider spraying only if 10 thrips per blossom are found when flowers are shaken onto a flat dark-colored surface and thrips are counted. A better way to sample thrips is to place randomly collected flower blossoms into a glass container with several drops of either ethyl acetate or methyl isobutyl ketone (or with a small amount of either of these chemicals soaked into cotton or other absorbent material). After at least one-half hour, count the thrips by removing the blossoms and shaking them onto black paper. Because more thrips will be found with this method, the treatment threshold is greater than that indicated for shaking flowers.

Common name Amount per acre REI‡ PHI‡
(Example trade name) (hours) (days)
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
 
(For increased efficacy, IRAC group 5 or 1B can be tank mixed with insecticides containing pyrethrins (group 3A). For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum rate of active ingredient on any label when tank mixing products that contain the same active ingredient.)
 
A. SPINOSAD
  (Entrust)# 1.25–2 oz 4 1
  (Success) 4–6 fl oz 4 1
  MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: Rotate to an insecticide with a different mode of action after two successive applications. Can be toxic to some natural enemies (e.g. predatory mites, syrphid fly larvae) when sprayed and shortly thereafter (8–24 hours). Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
B. SPINETORAM
  (Radiant SC) 6–10 fl oz 4 1
  MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: Rotate to an insecticide with a different mode of action after two successive applications of either spinetoram or spinosad to help delay the development of resistance to group 5 insecticides. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
C. MALATHION
  (Malathion 5EC) 1.5–3 pt 12 3
  (Malathion 8E) 1.5–2 pt 12 3
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: Residual activity only about 1 week. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
D. NALED
  (Dibrom 8EC) 1 pt 48 1
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: Do not use when temperature exceeds 85°F. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
E. ACETAMIPRID
  (Assail 70WP) 0.8–1.7 oz 12 1
  MODE-OF-ACTION GROUP NUMBER1: 4A
  COMMENTS: Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
F. BEAUVERIA BASSIANA#
  (BotaniGard ES) Label rates 4 0
  MODE-OF-ACTION GROUP NUMBER1:—
  ...PLUS...
  AZADIRACHTIN#
  (AzaGuard) Label rates 4 0
  MODE-OF-ACTION GROUP NUMBER1: un
  COMMENTS: An insect growth regulator.
 
G. ISARIA FUMOSOROSEA #
  (PFR-97 20% WDG) Label rates 4 0
  MODE-OF-ACTION GROUP NUMBER1: —
  ...PLUS...
  AZADIRACHTIN#
  (Neemix 4.5) Label rates 4 0
  MODE-OF-ACTION GROUP NUMBER1: un
  COMMENTS: An insect growth regulator.
 
H. PYRETHRIN/PIPERONYL BUTOXIDE
  (Pyrenone) Label rates 12 0
  MODE-OF-ACTION GROUP NUMBER1: 3A/ —
  COMMENTS: Variable efficacy. Not as disruptive of natural enemies as some other options.
 
I. PYRETHRIN#
  (PyGanic 1.4EC) 16–64 oz 12 0
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Apply in sufficient water for thorough coverage. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
Information not available.
# Acceptable for use on organically grown produce.
1 Rotate insecticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).
Text Updated: 07/18
Treatment Table Updated: 07/18