Description of the Pest
Western flower thrips adults are minute insects, about 0.03 inch long, with two pairs of fringed wings. The adult has three color forms that vary in abundance depending on the time of year. There is a pale form that is white and yellow, except for slight brown spots or blemishes on the top of the abdomen; an intermediate color form with an orange thorax and brown abdomen; and a dark form that is dark brown. The intermediate form is present throughout the year, but in spring the dark form predominates while the pale form is most abundant at other times throughout the year.
First-instar nymphs are opaque or light yellow, turning to golden yellow after the first molt. The nymphal stage lasts from 5 to 20 days.
Damage
At bloom, adult thrips insert eggs just under the surface of the developing fruit, causing fruit depressions or dimples as the fruit grows; a faint pansy spot may occasionally be visible around the puncture mark on green fruit but fortunately disappears as the fruit colors. Fruit is downgraded only if the egg-laying scars are numerous. Closer to harvest, high populations of thrips have been associated with the appearance of a silvery "halo" spot on mature fruit, particularly where fruit touch. Late-season damage is more common in Northwest growing areas than in California. In general, thrips damage is not common in California cherry orchards but has been seen in years when populations are exceptionally high during critical periods.
Management
Western flower thrips occasionally develop to high population levels in cherry. They overwinter as adults in weeds, grasses, alfalfa, and other hosts, either in the orchard floor or nearby. In early spring, if overwintering sites are disturbed or dry up, thrips migrate to flowering trees and plants on the orchard floor.
Cultural Control
Thrips are attracted to blossoms on trees as well as weeds blooming on the orchard floor. To prevent driving thrips into the trees, do not mow or disc the orchard vegetation when trees are in bloom. Open, weedy land adjacent to orchards should be disced as early as possible to prevent thrips development and migration of adults into orchards.
Organically Acceptable Methods
Cultural controls, clean cultivation, and sprays of the Entrust formulation of spinosad are organically acceptable tools.
Monitoring and Treatment Decisions
Begin monitoring thrips as individual blocks begin to bloom (see MONITORING PESTS AT BLOOM). In nectarines and peaches, thrips are monitored by slapping a shoot with five to ten blossoms against a yellow card or beating tray. A minimum of 50 trees per orchard should be checked for adults. In warm springs, adults may migrate in and out of a block. As thrips damage is uncommon in cherries, economic thresholds have not been established.
Continue to monitor orchards for thrips until fruit coloring. If fruit starts showing damage, a treatment may be necessary.
| Common name | Amount to use** | REI‡ | PHI‡ | ||
|---|---|---|---|---|---|
| (Example trade name) | (conc.) | (dilute) | (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. | |||||
| A. | SPINETORAM | ||||
| (Delegate WG) | 4.5–7 oz/acre | 4 | 7 | ||
| MODE-OF-ACTION GROUP NUMBER1: 5 | |||||
| COMMENTS: Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | |||||
| B. | SPINOSAD | ||||
| (Entrust)# | 1.25–2.5 oz | 0.42–0.83 oz | 4 | 7 | |
| (Success) | 4–8 fl oz | 1.3–2.7 fl oz | 4 | 7 | |
| MODE-OF-ACTION GROUP NUMBER1: 5 | |||||
| COMMENTS: Do not apply more than 29 oz/acre per year of Success or 9 oz/acre per year of Entrust. To avoid development of insect resistance, do not treat successive generations of the same pest with the same product. Control may be improved by addition of an adjuvant. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | |||||
| ** | For concentrate applications, use the amount given in 80–100 gal water/acre, or lower if the label allows; for dilute applications, amount is per 100 gal water to be applied in 300–400 gal water/acre, according to label. |
| ‡ | 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 use on organically grown produce. |
| 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). |