Agriculture: Apple Pest Management Guidelines

Western Flower Thrips

  • Frankliniella occidentalis
  • Description of the Pest

    Western flower thrips adults are minute insects, about 0.03 inch long, with two pairs of fringed wings. The adult has three color forms that vary in abundance depending on the time of year. There is a pale form that is white and yellow, except for slight brown spots or blemishes on the top of the abdomen; an intermediate color form with an orange thorax and brown abdomen; and a dark form that is dark brown. The intermediate form is present throughout the year, but in spring the dark form predominates while the pale form is most abundant at other times throughout the year.

    First-instar nymphs are opaque or light yellow, turning to golden yellow after the first molt. The nymphal stage lasts from 5 to 20 days.

    Damage

    Western flower thrips are attracted to the blossoms of apples as well as orchard cover crops and weeds. The primary damage is from egg-laying punctures in newly formed fruit, which typically occur before petal fall. The egg-laying site develops into tiny russetted spot surrounded by an irregular yellow patch known as a pansy spot (as it resembles the shape of a pansy). Granny Smith and other green varieties as well as Rome Beauty and McIntosh show more damage from this pest.

    Management

    Cultural Control

    Thrips are often attracted to weeds blooming on the orchard floor. To prevent driving thrips into the trees, do not disc the cover crop when trees are in bloom. Open, weedy land adjacent to orchards should be disced as early as possible to prevent thrips development and migration of adults into orchards.

    Organically Acceptable Methods

    Cultural controls and sprays of the Entrust formulation of spinosad are organically acceptable tools.

    Monitoring and Treatment Decisions

    Inspect for adult western flower thrips at 10% bloom. If several thrips, on the average, can be dislodged onto a sheet of paper by tapping individual flower clusters, a treatment may be needed to prevent damage.

    Harvest fruit sample

    At harvest, assess program by monitoring fruit in the bins for thrips damage. Sample 200 fruit per bin from 5 bins per orchard (or 20-acre block in large orchards).

    Common name Amount per acre REI‡ PHI‡
    (Example trade name) (conc.) (dilute) (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.
     
    A. SPINOSAD
    (Entrust)# 2–3 oz 4 7
    (Success) 3.5 oz 4 7
    MODE-OF-ACTION GROUP NUMBER1: 5
    COMMENTS: Control may be improved by addition of an adjuvant to the spray mixture. Do not apply more than 29 oz/acre per year of Success or 9 oz/acre per year of Entrust. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
     
    B. SPINETORAM
    (Delegate WG) 4.5–7 oz 4 7
    MODE-OF-ACTION GROUP NUMBER1: 5
      COMMENTS: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.
    # Acceptable for organically grown produce.
    1 Rotate chemicals 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; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode-of-action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    Text Updated: 12/09
    Treatment Table Updated: 10/15