How to Manage Pests

UC Pest Management Guidelines

Crop damaged by western flower thrips.

Pear

Thrips

Scientific names:
Pear thrips: Taeniothrips inconsequens
Western flower thrips: Frankliniella occidentalis

(Reviewed 11/12 , updated 11/12 )

In this Guideline:


DESCRIPTION OF THE PESTS

Thrips are minute, slender-bodied insects about 0.04 inch (1 mm) long. Some species of thrips are attracted to the blossoms of flowering plants, including apple and pear trees. Adult western flower thrips range from clear lemon yellow to yellow brown to dark brown in color. Adult pear thrips are dark brown to black in color. The wings are lighter, especially at their bases. The eyes are dark reddish brown. The larvae of pear thrips are white and possess a ring of dark spines on the underside toward the posterior end.

DAMAGE

Western flower thrips may damage pears grown in northern California. The primary damage is from egg punctures in newly formed fruit. Each puncture results in a slightly depressed russetted spot, between 0.125 and 0.25 inch (3 to 6 mm) in diameter. They also feed on the growing tips of newly planted trees, deforming tree growth.

The major damage seen with pear thrips in the past occurred during the period from green tip until bloom, when adults fed on fruit buds. This caused the buds to dry and die or to develop abnormally. Damaged buds produced droplets of gum, which help pinpoint a pear thrips infestation. In addition, pear thrips larvae fed on fruit causing russetting or scabbing of the surface; this resulted in deformed fruit.

MANAGEMENT

Once a common pear pest in California, the pear thrips is now rarely encountered, but western flower thrips can still be a problem.

Organically Acceptable Methods

Sprays of the Entrust formulation of spinosad are acceptable in an organically certified orchard.

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. For more information about monitoring at this time, see SAMPLING AT BLOOM.

Harvest fruit sample

At harvest, assess program by monitoring fruit in the bins for thrips. Sample 200 fruit per bin from 5 bins per orchard (or 20-acre block in large orchards). For more information regarding this sample, see HARVEST FRUIT SAMPLE.

Common name Amount to use R.E.I.+ P.H.I.+
(trade name)   (hours) (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 the label of the product being used.
 
BLOOM
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 per year of Success or 9 oz/acre per year of Entrust. Residual efficacy is affected by pH but initial efficacy is not; verify that water pH is greater than 6 and less than 8.
 
B. SPINETORAM
  (Delegate) 4.5–7 oz/acre 4 7
  MODE OF ACTION GROUP NUMBER1: 5
 
+ 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 www.irac-online.org.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455

Insects and Mites

L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County
R. B. Elkins, UC Cooperative Extension, Lake County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
C. Ingels, UC Cooperative Extension, Sacramento County
Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter/Yuba counties
P. W. Weddle, Weddle, Hansen & Associates
R. Hansen, Weddle, Hansen & Associates
P. Chevalier, United Ag Products, Ukiah
M. Hooper, Ag Unlimited, Lakeport
B. Knispel, Pest Control Adviser, Upper Lake
T. Lidyoff, Purity Products, Healdsburg
G. McCosker, Harvey Lyman Agservices, Walnut Grove
B. Oldham, Ag Unlimited, Ukiah
J. Sisevich, AgroTech, Kelseyville (retired)
D. Smith, Western Farm Service, Walnut Grove
B. Zoller, The Pear Doctor, Inc., Kelseyville

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