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How to Manage Pests

UC Pest Management Guidelines


Adult Western flower thrips.

Apple

Western Flower Thrips

Scientific Name: Frankliniella
occidentalis

(Reviewed 12/09, updated 12/09)

In this Guideline:


DESCRIPTION OF THE PESTS

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 Management 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
(trade name)
Amount to use R.E.I.+
(hours)
P.H.I.+
(days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to impact on natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. SPINOSAD
  (Entrust)# 1 oz/acre 4 7
  (Success) 3.5 oz/acre 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/year of Success or 9 oz/acre/year of Entrust.
   
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Apple
UC ANR Publication 3432
Insects and Mites
J. L. Caprile, UC Cooperative Extension, Contra Costa County
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
P. M. Vossen, UC Cooperative Extension, Sonoma and Marin counties
W. W. Coates, UC Cooperative Extension, San Benito County
H. L. Andris, UC Cooperative Extension, Fresno County
L. G. Varela, UC IPM Program, Sonoma County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, Sutter and Yuba counties

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