How to Manage Pests

UC Pest Management Guidelines

Citrus

Citrus Thrips

Scientific Name: Scirtothrips citri

(Reviewed 9/08, updated 3/09, corrected 6/13)

In this Guideline:


Description of the Pest

Adult citrus thrips are small, orange-yellow insects with fringed wings. During spring and summer, females lay about 25 eggs in new leaf tissue, young fruit, or green twigs; in fall, overwintering eggs are laid mostly in the last growth flush of the season. Overwintered eggs hatch in March about the time of the new spring growth. First-instar larvae are very small, whereas second-instar larvae are about the size of adults, spindle-shaped, and wingless. They feed actively on tender leaves and fruit, especially under the sepals of young fruit. Third- and fourth-instar (propupa and pupa) thrips do not feed and complete development on the ground or in the crevices of trees. When adults emerge, they move actively around the tree foliage.

Citrus thrips do not develop below 58°F (14°C). They can produce up to eight generations during the year if the weather is favorable.

When monitoring citrus thrips, you must be able to distinguish them from flower thrips, which feed on flower parts but do not damage citrus. Shortly after petal fall, immature flower thrips can be seen moving around young fruit, but they soon pupate and adults disperse to other plants, consequently they are only concentrated in citrus orchards for a short period in spring. For more information on distinguishing citrus thrips from other thrips, see Integrated Pest Management for Citrus, 3rd edition.

Damage

Citrus thrips is of greatest economic importance on San Joaquin navel oranges, desert citrus, and coastal lemons. On fruit, the citrus thrips punctures epidermal cells, leaving scabby, grayish or silvery scars on the rind. Second-instar larvae do the most damage because they feed mainly under the sepals of young fruit and are larger than first instars. As fruit grow, damaged rind tissue moves outward from beneath the sepals as a conspicuous ring of scarred tissue. Fruit are most susceptible to scarring from shortly after petal fall until they are about 1.5 inch (3.7 cm) in diameter. Thrips damage is higher on fruit located on the outside canopy where fruit is also susceptible to wind damage and sunburn.

Management

Citrus thrips populations can vary greatly from year to year. Monitor to determine if treatments are needed in a particular year. Navel oranges are more susceptible to damage than are Valencia oranges, which often do not require treatment.

Treatment of young, nonbearing trees in a grove is not recommended except in severe cases. Although the citrus foliage is often heavily damaged by citrus thrips, healthy trees can withstand the damage and frequent treatments can lead to the development of insecticide resistance, making control of thrips on fruit more difficult in later years.

Citrus thrips is less of a problem in orchards that receive minimal broad-spectrum pesticide treatments than in orchards that are heavily treated. Because of pesticide-induced hormoligosis (i.e. stimulation of thrips reproduction), thrips populations tend to increase after treatments with organophosphates, carbamates, pyrethroids, foliar neonicotinoids, and the miticide pyridaben (Nexter).

Biological Control

A number of natural enemies attack citrus thrips, including the predaceous mite Euseius tularensis, spiders, lacewings, dustywings, and minute pirate bugs. Some controversy exists regarding the degree of citrus thrips control afforded by E. tularensis populations; they provide some control but are also a very good "indicator" species, giving an indication of the level of general natural enemies present in an orchard. Citrus thrips population levels are aggravated when broad-spectrum pesticides are used, probably because of both a reduction in natural enemy levels and pesticide-induced hormoligosis.

In some years, when citrus thrips densities are excessively high, no amount of E. tularensis or other natural enemies in combination with selective pesticides can keep citrus thrips below an economic threshold.

Organically Acceptable Methods

Biological control is acceptable for use in organically managed orchards as well as sprays of the Entrust formulation of spinosad with an organically approved oil.

Resistance

Citrus thrips has a history of rapidly developing resistance to chemicals that are used repeatedly and frequently for its control. For example, resistance to dimethoate and formetanate hydrochloride (Carzol) has developed in a number of citrus thrips populations in the San Joaquin and Coachella valleys; beta-cyfluthrin (Baythroid) and fenpropathrin (Danifol) resistance has appeared in several groves in Kern County. With the limited number of pesticides available for control of citrus thrips now and in the foreseeable future, it is wise to monitor citrus thrips levels carefully, to limit treatments only to populations that are causing or are expected to cause significant levels of fruit scarring (treatments to prevent foliar damage are not recommended), and to time and apply treatments optimally so that reapplications are not required. Although citrus thrips disperse a good deal, citrus thrips resistance problems are often localized. Thus, growers using repeated applications for citrus thrips control are most likely to experience resistance problems at a later date.

Selectivity

The botanical insecticide sabadilla (Veratran) and spinetoram (Delegate), spinosad (Success or Entrust) and abamectin (Agri-Mek, etc.) are relatively nontoxic to beneficial insects and mites. The broad-spectrum organophosphate (dimethoate), carbamate (formetanate hydrochloride–Carzol), and pyrethroids (beta-cyfluthrin–Baythroid, fenpropathrin-Danitol) insecticides are toxic and fairly persistent against both beneficial mites and beneficial insects and disrupt biological control.

Monitoring

Check young fruit for immature thrips and monitor the undersurface of inside foliage for predaceous mites. Monitor from petal fall until fruit is greater than 1.5 inches in diameter. For oranges, the monitoring time is about 6 to 8 weeks in spring. For lemons, monitor June through October.

Monitoring Fruit for Citrus Thrips

Select trees that are three to four rows in from the outside edge of the block. Sample 25 young fruit from each corner of the block for a total of 100 fruit. Take only one to two healthy, dark green fruit from outside, sunny branches of each tree. Look for thrips on the stem end of the fruit under the calyx. Count fruit as infested only if it has one or more wingless first-or second-instar nymphs (ignore pupae and adults). Record the total fruit infested with immature citrus thrips and calculate the percentage of infested fruit (example formPDF). On very susceptible varieties, such as San Joaquin Valley navels, monitor fruit at least twice a week after petal fall, and continue monitoring as long as susceptible fruit is on the tree.

Monitoring Predatory Mites

Examine the underside of twenty 5-leaf terminals with fully expanded leaves from shady areas of the canopy (a total of 100 leaves), and count the number of adult predatory mites. Calculate and record the average number of predatory mites per leaf (example form A minimum of 0.5 predatory mites per leaf is needed to assist with biological control of citrus thrips.

Treatment Decisions

Treatment thresholds vary by growing region, cultivar, beneficial mite populations, and the type of miticide that will be applied. A significant factor affecting threshold levels is whether the orchard is sheltered from wind damage (lower threshold) or has a history of outside fruit scarring from seasonal winds (higher threshold). As fruit get larger, treatment thresholds go up. Less susceptible varieties, such as Valencia oranges, may not require monitoring or treatment.

Sabadilla (Veratran), spinetoram (Delegate), spinosad (Entrust, Success), or abamectin (Agri-Mek, etc.) are recommended to avoid severe mortality of natural enemies. Sabadilla is a stomach poison that contains sugar or molasses as a bait and must be consumed by the thrips in order to be effective. When a treatment of sabadilla, spinetoram, spinosad, or abamectin is planned, beneficial mite populations are considered significant if you have more than 0.5 predator per leaf. Just after petal fall, treatment thresholds are as follows:

  • Valencia oranges: 10% of fruit sampled with one or more immature citrus thrips and few predators present, or 20% infested in the presence of significant levels of beneficial mites. Raise these thresholds as fruit grow
  • Navel oranges: 5% of fruit sample infested and few predators present, or 10% infested with significant levels of beneficial mites. Raise these thresholds as fruit grow

Dimethoate, formetanate hydrochloride (Carzol), beta-cyfluthrin (Baythroid), and fenpropathrin (Danitol) are contact poisons and are most effective when applied shortly before the majority of citrus thrips hatch (when 5% or less of the fruit are infested with first instar citrus thrips). On very susceptible varieties, such as San Joaquin Valley navel oranges, monitor fruit at least twice a week after petal fall. Less susceptible varieties such as Valencia oranges may not require treatment. Optimal timing of these contact materials is usually shortly after petal fall but can be delayed depending on weather and on thrips development. If an application of dimethoate, formetanate hydrochloride, cyfluthrin, or fenpropathrin is planned, the threshold is 1 to 5% infested fruit on navel oranges. Do not treat citrus thrips prebloom or after fruit exceed 1.5 inches in diameter, unless severe populations are present.

Because of the continuous fruiting nature of coastal lemons, a treatment threshold of between 10 to 20% infested fruit is used, depending on whether the orchard is sheltered from wind damage (lower threshold) or has a history of outside fruit scarring from seasonal winds (higher threshold).

When monitoring indicates a treatment may be needed, it is essential to properly time and apply a treatment in order to reduce the likelihood of a second treatment being needed, and thus reduce the long-term development of resistance. Apply the treatment using outside coverage (OC) by reducing spray blower wind velocity. Ground application is more effective than air application and 200 gallons per acre is more effective than lower or higher gallonage, except with the sugar or molasses bait treatments using sabadilla. Because of their smaller size, coastal lemon trees receive adequate control with an aerial application. Firm data on optimal gallonage with sugar baits are not available, but some growers believe that lower gallonage is more effective because the sugar concentration is increased. Don't apply sabadilla and a sugar bait just before or during periods of heavy dew, fog, or drizzle. Such weather conditions cause the sugar bait to separate from the toxin, rendering the treatment ineffective.

Common name Amount to use R.E.I.‡ P.H.I.‡
(example trade name) (type of coverage)** (hours) (days)

  Calculate impact of pesticide on air quality
 
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. SABADILLA
  (Veratran D) 10–20 lb/acre PLUS up to 24 When dry
  10 lb sugar in 50–200 gal (OC)    
  RANGE OF ACTIVITY: Pests: narrow (citrus thrips); Natural enemies: predatory thrips
  PERSISTENCE: Pests: very short; Natural enemies: very short
  COMMENTS: For use on all varieties. Acidify water in the spray tank to a pH of 4.5 before adding sabadilla; use citric acid or other approved acidifying agents. Most effective if substantial numbers of predators such as the predaceous mite Euseius tularensis are present. Sabadilla is a short residual stomach poison; time application of this material to coincide with mid-hatch. Most effective during warm weather; in cool weather thrips don't feed well on bait and it degrades with time. Use higher rates with more dilute applications. Do not combine with fertilizers because this reduces feeding by the thrips on the bait. Ground application at 3 mph with reduced wind velocity so as to achieve outside coverage. Don't apply during periods of heavy dew, fog, or drizzle.
 
B. SPINETORAM
  (Delegate) WG 3-6 oz/acre (OC) 4 1
  RANGE OF ACTIVITY: Pests: narrow (thrips, orangeworms, katydids); Natural enemies: predatory thrips
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  MODE OF ACTION GROUP NUMBER1: 5
  . . . PLUS . . .
  NARROW RANGE OIL#
  (415) 0.25-1% 4 When dry
  RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
  PERSISTENCE: Pests: short; Natural enemies: short
  MODE OF ACTION: Improves translaminar movement and insecticide persistence.
  COMMENTS: For use on all varieties. Do not apply to citrus nurseries or to citrus in greenhouses. Most effective if substantial numbers of predators such as the predaceous mite Euseius tularensis are present. Time application to coincide with early to mid-hatch (see the thresholds listed above). To avoid potential phytotoxicity of oil to the fruit, do not apply 30 days before or after a sulfur application, and do not apply to small fruit (less than 1 inch in diameter) on a day when the ambient temperature has or is expected to exceed 95°F or when the relative humidity has or is expected to drop below 20%. Use ground application at 3 mph with reduced wind velocity so as to achieve outside coverage. Repeated applications will result in citrus thrips resistance. For resistance management purposes, do not apply Mode of Action Group 5 insecticides (spinetoram and spinosad) more than twice a year. Do not apply more than a total of 12 oz/acre per crop.
 
C. SPIROTETRAMAT
  (Movento) 2SC 8-10 fl oz/acre (OC) 24 1
  RANGE OF ACTIVITY: Pests: broad (mites, thrips, leafminers, aphids, armored scales); Natural enemies: predatory mites
  PERSISTENCE: Pests: long; Natural enemies: short (except via leaf or host feeding)
  MODE OF ACTION GROUP NUMBER1: 23
  . . . PLUS . . .
  NARROW RANGE OIL#
  (415) 0.25-1% 4 When dry
  RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
  PERSISTENCE: Pests: short; Natural enemies: short
  MODE OF ACTION: Improves translaminar movement and insecticide persistence.
  COMMENTS: For use on all varieties. Most effective if substantial numbers of predators such as the predaceous mite Euseius tularensis are present. Time application to coincide with early to mid-hatch (see the thresholds listed above). To avoid potential phytotoxicity of oil to fruit, do not apply 30 days before or after a sulfur application, and do not apply to small fruit (less than 1 inch in diameter) on a day when the ambient temperature has or is expected to exceed 95°F, or when the relative humidity has or is expected to drop below 20%. Use ground application at 3 mph with reduced wind velocity so as to achieve outside coverage unless the treatment is also intended for red scale control, in which case intermediate coverage and 500 or so gpa might be best. Must be applied with oil or an adjuvant to improve penetration. Do not apply before bloom, during bloom, or 10 days after petal fall. Repeated applications will result in citrus thrips resistance. For resistance management purposes, do not apply more than once a year (i.e., do not apply in spring for citrus thrips management and in summer for red scale).
 
D. SPINOSAD
  (Entrust) 80WP# 3 oz/acre (OC) 4 1
  (Success) 2SC 4-6 fl oz/acre (OC) 4 1
  RANGE OF ACTIVITY: Pests: narrow (thrips, orangeworms, katydids); Natural enemies: predatory thrips
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  MODE OF ACTION GROUP NUMBER1: 5
  . . . PLUS . . .
  NARROW RANGE OIL#
  (415) 0.25-1% 4 When dry
  RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
  PERSISTENCE: Pests: short; Natural enemies: short
  MODE OF ACTION: Improves translaminar movement and insecticide persistence.
  COMMENTS: For use on all varieties. Most effective if substantial numbers of predators such as the predaceous mite Euseius tularensis are present. Time application to coincide with early to mid-hatch (see the thresholds listed above). To avoid potential phytotoxicity of oil to the fruit, do not apply 30 days before or after a sulfur application, and do not apply to small fruit (less than 1 inch in diameter) on a day when the ambient temperature has or is expected to exceed 95°F or when the relative humidity has or is expected to drop below 20%. Use ground application at 3 mph with reduced wind velocity so as to achieve outside coverage. Repeated applications will result in citrus thrips resistance. For resistance management purposes, do not apply Mode of Action Group 5 insecticides (spinetoram and spinosad) more than twice a year. Do not apply to citrus nurseries or to citrus in greenhouses.
 
E. ABAMECTIN*
  (Agri-Mek, etc.) 10 fl oz/acre (OC) 12 7
  RANGE OF ACTIVITY: Pests: intermediate (citrus thrips, mites, leafminers); Natural enemies: predatory mites and thrips
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  MODE OF ACTION GROUP NUMBER1: 6
  . . . PLUS . . .
  NARROW RANGE OIL
  (415) 0.25-1% 4 when dry
  MODE OF ACTION: Improves translaminar movement and insecticide persistence.
  RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
  PERSISTENCE: Pests: short; Natural enemies: short
  COMMENTS: For use on all varieties. Apply in 50–250 gal water/acre. Do not apply in citrus nurseries. To avoid potential phytotoxicity of oil to the fruit, do not apply 30 days before or after a sulfur application and do not apply to small fruit (less than 1 inch in diameter) on a day when the ambient temperature has or is expected to exceed 95°F or when the relative humidity has or is expected to drop below 20%. Most effective if substantial numbers of predators such as the predaceous mite, Euseius tularensis, are present. Time application to coincide with early to mid-hatch (see the thresholds listed above). Use ground application at 3 mph with reduced wind velocity so as to achieve outside coverage. Repeated applications will result in citrus thrips resistance.
   
F. BETA-CYFLUTHRIN*
  (Baythroid XL) 6.4 fl oz/acre (OC) 12 0
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate (low rates), long (high rates)
  RESISTANCE: in some citrus thrips populations in the San Joaquin Valley
  MODE OF ACTION GROUP NUMBER1: 3A
  COMMENTS: Only a single application may be made per crop season. To reduce the potential for resistance, make a total of only one pyrethroid application (for all pest species) per year or, if feasible, only one application every 2 to 3 years. Do not apply within 25 feet of lakes, reservoirs, rivers, permanent streams, marshes, or natural ponds, estuaries, and commercial fish farm ponds.
 
G. FENPROPATHRIN*
  (Danitol) 2.4 EC 21.33 fl oz/acre (OC) 24 1
  RANGE OF ACTIVITY: Pests: broad (many insects and mites); Natural enemies: most
  PERSISTENCE: Pests: intermediate; Natural enemies: long
  RESISTANCE: in some citrus thrips populations in the San Joaquin Valley
  MODE OF ACTION GROUP NUMBER1: 3A
  COMMENTS: Apply in 50–200 gal water/acre. Use only on citrus trees 3 years or older. To reduce the potential for resistance, make a total of only one pyrethroid application (for all pest species) per year or, if feasible, only one application every 2 to 3 years. Do not apply in the vicinity of aquatic areas.
   
H. FORMETANATE HYDROCHLORIDE
  (Carzol) 92SP 1–1.25 lb/acre (OC) See comments See comments
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: intermediate; Natural enemies: long, unless washed off
  RESISTANCE: in some citrus thrips populations
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: For use on oranges, lemons, limes, tangerines, tangelos, and grapefruit. Apply at the beginning of hatch; less effective if resistance has developed. Do not apply after fruit reach a diameter of one inch. If unharvested grapefruit and Valencia oranges are present from the previous crop, an application may be made to the new crop. However, a preharvest interval of 30 days must be observed for the unharvested crop. R.E.I. is 10 days for weeding and propping; 16 days for harvesting, thinning, topping, and pruning. Ground application at 3 mph with reduced wind velocity so as to achieve outside coverage.
 
I. DIMETHOATE
  (Dimethoate 400) 4EC 1 qt/acre in 100–200 gal (OC) 14 days 15
    . . . or . . .  
    in 20 gal (A)  
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: intermediate; Natural enemies: long
  RESISTANCE: in some citrus thrips populations
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: For use on oranges, grapefruit, lemons, tangerines. No more than 2 applications on mature fruit. Apply at the beginning of hatch. Less effective if resistance has developed. Ground application at 3 mph with reduced wind velocity so as to achieve outside coverage.
  . . . or . . .
  (Dimethoate 2.67) 2–3 pt/acre in 100–200 gal (OC) 14 days 15
    . . . or . . .  
    in 20 gal (A)  
  COMMENTS: For use on oranges, grapefruit, lemons, tangerines. No more than 2 applications on mature fruit. Apply at the beginning of hatch. Less effective if resistance has developed. Ground application at 3 mph with reduced wind velocity so as to achieve outside coverage.
 
** A - Aircraft applications 5-20 gal/acre
  OC - Outside coverage uses 100–250 gal water/acre.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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.
* Permit required from county agricultural commissioner for purchase or use.
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 ("un"=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441

Insects, Mites, and Snails

  • E. E. Grafton-Cardwell, Entomology, UC Riverside and Kearney Agricultural Center, Parlier
  • J. G. Morse, Entomology, UC Riverside
  • N. V. O'Connell, UC Cooperative Extension, Tulare County
  • P. A. Phillips (emeritus), UC IPM Program, UC Cooperative Extension, Ventura County
  • C. E. Kallsen, UC Cooperative Extension, Kern County
  • D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgments for contributions to Insect, Mites, and Snails:
  • J. Barcinas, E.S.I., Corona, CA
  • R. Dunn, Badger Farming Co., Exeter, CA
  • J. Gorden, Pest Management Associates, Exeter, CA
  • H. Griffiths, E.S.I., Corona, CA
  • D. Machlitt, Consulting Entomology Services, Moorpark, CA
  • C. Musgrove, retired entomologist, Riverside, CA
  • K. Olsen, S & J Ranch, Pinedale, CA
  • T. Roberts, E.S.I., Corona, CA
  • T. Shea, UC Cooperative Extension, Riverside County
  • J. Stewart, Pest Management Associates, Exeter, CA
  • P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA

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