UC IPM: UC Management Guidelines for Western Flower Thrips on Plum

UC Pest Management Guidelines

Plum

Western Flower Thrips

Scientific name: Frankliniella occidentalis

(Reviewed 5/06, updated 5/06)

In this Guideline:

Description of the pest
Damage
Management

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**

P.H.I.+

(trade name)

(conc.)

(dilute)

(days)

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.

SPINOSAD

(Entrust)#

1.71–2.5 oz

0.43–0.6 oz

(Success)

6–8 oz

1.5–2 oz

MODE OF ACTION: A microbial (Group 5)¹ insecticide.

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.

DIAZINON* 50WP

1.5–3 lb

1 lb

DIAZINON* 4EC

2 pt

0.5 pt

MODE OF ACTION: An organophosphate (Group 1B)¹ insecticide.

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.
+	Preharvest interval. Do not apply within this many days of harvest.
*	Permit required from county agricultural commissioner for purchase or use.
¹	Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

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 the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier

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