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UC Pest Management Guidelines


Adult western flower thrips, Frankliniella occidentalis.

Plum

Western Flower Thrips

Scientific name: Frankliniella occidentalis

(Reviewed 5/06, updated 4/09)

In this Guideline:


DESCRIPTION OF THE PEST

Western flower thrips adults are yellow brown to straw colored and about 0.05 inch long. Adults have four wings that are long and narrow with a fringe of long hairs on the margins. Immatures resemble adults except they are smaller and lack wings. Western flower thrips overwinter as adults in trash and have many generations each year.

DAMAGE

Thrips nymphs damage to plums in the Central Valley can be serious, especially on thin-skinned varieties. In early warm seasons, plums suffer little damage; however, if the season is cool and bloom occurs over a long period of time, damage can occur. Damage consists of several types: holes or depressions with a halo around them, thrips egg punctures or pansy spots, and thrips scarring in large or small blotches. All three types of damage can result in fruit being culled.

MANAGEMENT

To reduce thrips migration to blossoms, avoid discing or mowing orchard cover crops or allowing them to dry out when trees are in bloom. Also avoid discing adjacent weedy areas or mowing alfalfa. Begin monitoring for thrips at the start of bloom. Check for presence of nymphs and adults by shaking or knocking flower clusters on to a light yellow painted board or clip board. To find nymphs, dissect flowers. Treat, if necessary, at petal fall based on monitoring and observing thrips in the flowers.

Common name Amount to Use** R.E.I.+ P.H.I.+
(trade name) (conc.) (dilute) (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, impact on natural enemies and honey bees, and impact of the timing on beneficials. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. SPINOSAD
  (Entrust)# 1.71–2.5 oz 0.43–0.6 oz 4 7
  (Success) 6–8 oz 1.5–2 oz 4 7
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: To avoid development of insect resistance, do not treat successive generations of the same pest with the same product. Do not apply more than 29 oz/acre/year of Success or 9 oz/acre/year of Entrust. This product is toxic to bees for 3 hours following treatment; apply in late evening after bees have stopped foraging.
 
B. DIAZINON* 50WP 1.5–3 lb 1 lb 24 21
                        4EC 2 pt 0.5 pt 24 21
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Avoid drift and runoff into surface waters. Where plums are grown near waterways, do not use diazinon.
 
** For dilute applications, rate is per 100 gal water to be applied in 300-500 gal water/acre, according to label; for concentrate applications, use 80-100 gal water/acre, or lower if the label allows.
+ 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.
* Permit required from county agricultural commissioner for purchase or use.
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: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier

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