Description of the Pest
Thrips are small insects, 0.04 inch long, with distinctive feathery wings. Color varies from yellow to brown in color. Grape thrips and western flower thrips are the most important species causing damage on grapes. Both species may be found in most grape-growing areas. Grape thrips populations usually reach their greatest numbers in July; this coincides with peak vine growth, and as vine growth slows, the numbers of thrips decreases. Western flower thrips populations peak in May, coinciding with grape bloom and the drying up of winter plant hosts.
Damage
Table grapes are susceptible to fruit damage caused by the western flower thrips. They create halo-spotting on the fruit when they oviposit in berries during bloom and up to fruit set or shortly thereafter. Both western flower thrips and grape thrips can scar berries with their feeding, which renders certain white varieties used for table grapes unmarketable. Thrips scarring is primarily a problem on Red Globe, Calmeria, Italia, and occasionally on Thompson Seedless. Fruit feeding discontinues in summer when both species feed on new vegetative growth.
In the North Coast, western flower thrips can feed in emerging shoots in early spring and stunt shoots and cause leaves to cup, especially during cool, rainy springs. Grape thrips may attack shoot tips in late spring or early summer although damage does not become apparent until the population has already decreased. While summer damage of leaves by thrips is common, it is not considered a problem for most varieties. However, a heavy grape thrips population can be a problem in Salvadors.
Management
In general, thrips are a minor problem on wine and raisin grapes in California with the exception of large populations on emerging shoots in cool growing regions; however, table grapes are susceptible to thrips damage and may require treatment. For table grapes, make thrips management decisions based on pest population and damage in previous years and varietal susceptibility.
Biological Control
Little is known about natural control of thrips in vineyards but predators such as minute pirate bugs undoubtedly play a role in keeping populations in check.
Cultural Control
Avoid mowing cover crops infested with thrips at budbreak or before bloom because thrips may move to vines and cause shoot stunting.
Organically Acceptable Methods
Biological and cultural controls and sprays of the Entrust formulation of spinosad and certain narrow range oils are acceptable in organically managed vineyards; check with your certifier for details.
Monitoring and Treatment Decisions
On cool days after budbreak monitor for thrips. Open shoots or gently tap buds over white paper to check for thrips.
Table Grapes
During the period of rapid shoot growth, inspect flowers or fruit clusters for adults or larvae, as well as the predatory minute pirate bug, by striking clusters three times over a white piece of cardboard. Normal population levels of western flower thrips range from 5 to 25 adults and 10-50 larvae per cluster. High levels exceed 150 adults and 300 larvae per cluster, but damaging population levels for grape thrips in clusters has not been determined. Bloom sprays may be necessary to prevent berry scarring in table grape vineyards.
At harvest look for damage caused by thrips to assess this year's management program and to plan for next year.
Wine Grapes
From dormancy through budbreak, monitor for thrips along with other pests in wine/raisin grapes as outlined in DORMANT/DELAYED DORMANT AND BUDBREAK MONITORING. Inspect new shoots in spring, especially in cool regions, for shoot scarring and distorted leaves. In these areas treatment may be necessary if damage increases and cool temperatures persist. Record observations on a monitoring form (example form—.
| Common name | Amount per acre** | 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. | ||||
| A. | SPINETORAM | |||
| (Delegate WG) | 3–5 oz | 4 | 7 | |
| MODE-OF-ACTION GROUP NUMBER1: 5 | ||||
| COMMENTS: A stomach poison; most effective when ingested. To protect honey bees, apply only during late evening, night, or early morning when bees are not present. | ||||
| B. | SPINOSAD | |||
| (Entrust)# | 1.25–2.5 oz | 4 | 7 | |
| (Success) | 4–8 fl oz | 4 | 7 | |
| MODE-OF-ACTION GROUP NUMBER1: 5 | ||||
| COMMENTS: Apply when eggs first hatch to target the young larvae. Heavy infestations require a second application in 4 or 5 days. To protect honey bees, apply only during late evening, night, or early morning when bees are not present. | ||||
| C. | FENPROPATHRIN* | |||
| (Danitol 2.4EC) | 10.33–21.22 fl oz | 24 | 21 | |
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: To protect honey bees, apply only during late evening, night, or early morning when bees are not present. Disruptive to beneficial insects. | ||||
| D. | NARROW RANGE OIL# | |||
| (JMS Organic Stylet Oil) | 1–2 gal | See label | See label | |
| MODE OF ACTION: Contact including smothering and barrier effects. | ||||
| COMMENTS: Use for thrips control early in the season; do not use for flower thrips in table grapes. Apply early in the season from 1-inch shoot length until set. Will help prevent shoot damage in early spring but not effective for berry scarring. Commonly used when shoot growth is slowed by cool, spring temperatures. (Also controls mites and serves as a contact treatment for powdery mildew in spring.) Using ground equipment, spray for optimum coverage of leaf surfaces. Repeat sprays every 1 to 14 days. Late season applications may leave a residue on post-veraison berries. Do not apply with copper when fruit is present; do not apply within 10 days of sulfur. Read label carefully for other use restrictions. | ||||
| ** | Apply with enough water to provide complete coverage. |
| ‡ | 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. |
| * | Permit required from county agricultural commissioner for purchase or use. |
| # | Acceptable for use on 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). |