How to Manage Pests

UC Pest Management Guidelines

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.)

PUBLICATION

UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension Sonoma Co.
R. B. Elkins, UC Cooperative Extension Lake Co.
R. A. Van Steenwyk, Insect Biology, UC Berkeley
C. Ingels, UC Cooperative Extension Sacramento Co.
Acknowledgment for contributions to the insects and mites section:
C. Pickel, UC IPM Program, UC Cooperative Extension Sutter/Yuba counties
P. W. Weddle, Weddle, Hansen & Associates
P. Chevalier, United Ag Products, Ukiah; B. Knispel, United Ag Products, Kelseyville
T. Lidyoff, Purity Products, Healdsburg; G. McCosker, AgroTech, Kelseyville
B. Oldham, Ag Unlimited, Ukiah
D. Smith, Western Farm Service, Walnut Grove
J. Sisevich, AgroTech, Kelseyville
B. Zoller, The Pear Doctor, Inc., Kelseyville

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