Description of the Pest
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.
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.
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||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|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.|
|MODE OF ACTION GROUP NUMBER1: 5|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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).|