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.
Biological and cultural controls and sprays of the Entrust formulation of spinosad and certain narrow range oils (mineral oil) 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—.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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|
Danitol 2.4 EC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
10.33–21.22 fl oz | 24 | 21 | To protect honey bees, apply only during... | broad | high | high | high | — | high | high | extra high | very low | very low | 07/2015 | ||
|
|
Organic JMS Stylet-Oil # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
UNM |
1–2 gal | See label | See label | Narrow range oil. Use for thrips control... | broad | low | low | low | none to short | very low | low | very low | very low | very low | 07/2015 | ||
|
|
Delegate WG | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
3–5 oz | 4 | 7 | A stomach poison; most effective when in... | narrow | low/moderate | moderate 13 | moderate/high | moderate 14 | low | low | low | very low | low | 07/2015 | ||
|
|
Entrust # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
1.25–2.5 oz | 4 | 7 | Apply when eggs first hatch to target th... | narrow | low | moderate 13 | low/moderate | short | very low | low | low | very low | low | 07/2015 | ||
|
|
Success | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
4–8 fl oz | 4 | 7 | Apply when eggs first hatch to target th... | narrow | low | moderate 13 | low/moderate | short | very low | low | low | very low | low | 07/2015 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # a b Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 a b c Toxic to some natural enemies (lacewing and syrphid fly larvae, predatory beetles, and thrips) when sprayed and up to 5 to 7 days after.
- 14 ↩ Residual is moderate if solution is between a pH of 7 and 8.
Important Links
UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
L.G. Varela (emeritus), UC IPM and UC Cooperative Extension Sonoma County
D.R. Haviland, UC IPM and UC Cooperative Extension Kern County
W.J. Bentley (emeritus), UC IPM and Kearney Agricultural Research and Extension Center, Parlier
L.J. Bettiga, UC Cooperative Extension Monterey County
K.M. Daane, Kearney Agricultural Research and Extension Center, Parlier
R.J. Smith (emeritus), UC Cooperative Extension Sonoma County
L.R. Wunderlich, UC Cooperative Extension Central Sierra
F.G. Zalom (emeritus), Entomology, UC Davis
Acknowledgement for Contributions to Invertebrates
M.C. Battany, UC Cooperative Extension San Luis Obispo County
J. Granett (emeritus), Entomology, UC Davis
P.A. Phillips (emeritus), UC Cooperative Extension Ventura County
A.H. Purcell (emeritus), Environmental Science, Policy, and Management, UC Berkeley
