Agriculture

Thrips

  • Onion thrips: Thrips tabaci and other species
  • Western flower thrips: Frankliniella occidentalis
Updated: 11/2012

Tools

PestManage: a decision support tool to view and compare pest management options

Description of the Pest

Thrips are very small, slender insects that are best seen with a hand lens. Mature western flower thrips are 0.06 inch (1.5 mm) long, while onion thrips are slightly smaller at 0.05 inch (1.3 mm) long. The most distinctive characteristic of thrips is two pairs of wings that are fringed with long hairs. Adults are pale yellow to light brown in color. Immature stages have the same body shape as adults but are lighter in color and are wingless. Western flower thrips adults have red-colored pigment in their simple eyes (ocelli) while onion thrips' simple eyes are gray.

Thrips have a very extensive host range, including cereals, onions, garlic, and broadleaved crops, but it is only the species of plants that are infected by tomato spotted wilt virus and on which the thrips can complete their entire life cycle that play an important role in the disease cycle. In California, the key crop hosts include tomato, pepper, lettuce, radicchio and fava bean. Important weed hosts include little mallow (Malva parviflora), sowthistle (Sonchus oleraceus), and prickly lettuce (Lactuca serriola).

The adults are the only life stage that can fly, but they are not strong fliers. Adult thrips can be carried on wind currents, on clothing, and in association with plants. The length of the thrips life cycle (from egg to adult) varies depending on environmental conditions, but is generally 30-45 days, though it can be as little as 14 days.

Damage

The primary damage caused by thrips to peppers is the vectoring of Tomato spotted wilt virus. The virus can only be acquired by the immature stage of thrips, whereas plant-to-plant transmission primarily occurs by adults. The adult thrips can transmit the virus for the remainder of their lives, which can last 30 to 45 days. However, the adults do not pass the virus to their progeny through the egg.

High populations of thrips can cause damage with their feeding, which distorts plant growth, deforms flowers, and causes white-to-silvery patches on emerging leaves that often have tiny black fecal specks in them.

Management

If possible, avoid planting peppers next to onions, garlic, or cereals, because thrips often build up to large numbers on these crops. Also, avoid fields near greenhouses where ornamentals (cut flowers) are grown, as these plants serve as hosts for thrips and the virus they transmit.

Use reflective mulches early in the season to repel thrips. Put up yellow sticky traps, which are also useful for monitoring aphids, whiteflies, and tomato psyllid, and monitor the movement of thrips.

Insecticide treatments for thrips are usually not warranted in the Imperial Valley but may be needed for suppression of Tomato spotted wilt virus in the San Joaquin Valley and coastal growing areas. If thrips are present, treat seedlings and transplants with imidacloprid (treat transplants before placement in the field and at planting). Treating plants with foliar insecticide sprays throughout the season on a need basis may limit in-field spread of Tomato spotted wilt virus to some extent. Rotate classes of insecticides to minimize insecticide resistance in thrips.

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
G
Dimethoate 400 Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

1B

0.5–0.6 pt 48 0 Do not use if psyllids are present. Effi... broad I high high high long very low low low intermediate high 06/2016
G
Dimethoate E267 Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

1B

0.75–1 pt 48 0 Do not use if psyllids are present. Effi... broad I high high high long — — — — — 06/2016
H
Beleaf 50 SG Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

29

2.8–4.28 oz 12 0 — narrow III low low low short very low very low low low intermediate 06/2016
A
Admire Pro Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

4A

1.3–2.2 fl oz 12 0 Spray transplants 3 to 7 days before pla... narrow I — low low long — — — — — 06/2016
B
Admire Pro Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

4A

7–14 fl oz 12 21 Apply through drip at planting or as a b... narrow I — low low long — — — — — 06/2016
E
*
Lannate LV Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

1A

0.75–1.5 pt 48 3 Do not use if psyllids are present. Effi... broad I high high high moderate — — — — — 06/2016
E
*
Lannate SP Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

1A

0.25–0.5 lb 48 3 Do not use if psyllids are present. Effi... broad I high high high moderate — — — — — 06/2016
C
Radiant SC Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

5

6–10 fl oz 4 1 Toxic to bees; do not spray directly or... narrow II moderate moderate 13 low/moderate moderate 14 low low low very low low 06/2016
D
Entrust # Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

5

1.25–2.5 oz 4 1 Toxic to bees; do not spray directly or... narrow II moderate moderate 13 low/moderate moderate 13 very low low low very low low 06/2016
D
Success Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

5

4–8 oz 4 1 Toxic to bees; do not spray directly or... narrow II moderate moderate 13 low/moderate moderate 13 very low low low very low low 06/2016
F
Movento Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

23

4.0–5.0 fl oz 24 1 — narrow II — — — — low very low low very low low 06/2016
—
No information.
I
Do not apply or allow to drift to plants that are flowering including weeds. Do not allow pesticide to contaminate water accessible to bees including puddles.
II
Do not apply or allow to drift to plants that are flowering including weeds, except when the application is made between sunset and midnight if allowed by the pesticide label and regulations. Do not allow pesticide to contaminate water accessible to bees including puddles.
III
No bee precaution, except when required by the pesticide label or regulations.
  • ‡ 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  Permit required from county agricultural commissioner for purchase or use.
  • # ↩  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 d e 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.
UC Peer Reviewed Logo

UC IPM Pest Management Guidelines: Peppers
UC ANR Publication 3460

E.T. Natwick (emeritus), UC Cooperative Extension Imperial County

J.T. Trumble, Entomology, UC Riverside

J.L. Aguiar, UC Cooperative Extension Riverside County

Acknowledgement for Contributions to Invertebrates

W.J. Bentley (emeritus), UC IPM and Kearney Agricultural Research and Extension Center, Parlier

W.E. Chaney (emeritus), UC Cooperative Extension Monterey County

R.L. Coviello, UC Cooperative Extension Fresno County

C.F. Fouche, UC Cooperative Extension San Joaquin County

C.G. Summers (emeritus), Entomology, UC Davis and Kearney Agricultural Research and Extension Center, Parlier

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