How to Manage Pests

UC Pest Management Guidelines

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 UC ANR Publication 3303, Integrated Pest Management for Citrus, 2nd 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.

Citrus thrips is less of a problem in orchards that receive minimal pesticide treatments than in orchards that are heavily treated. Thrips populations tend to increase after treatments with organophosphates and carbamates because of the reduction of natural enemies and because of pesticide-induced stimulation of the citrus thrips reproduction.

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 a pesticide-induced hormoligosis (stimulation of thrips reproduction).

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.

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; cyfluthrin (Baythroid) 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 the natural products spinosad (Success) and abamectin (Agri-Mek) are relatively nontoxic to beneficial insects and mites. The broad-spectrum organophosphate (dimethoate), carbamate (formetanate hydrochloride–Carzol), and pyrethroids (cyfluthrin–Baythroid, fenpropathrin-Danitol) insecticides are toxic to both beneficial mites and beneficial insects and disrupt biological control.

Monitoring and Treatment Decisions
Check young fruit for immature citrus thrips and monitor the undersurface of inside foliage for predaceous mites. Recommended sample size is 25 fruit from each corner of the block for citrus thrips (a total of 100) and five 5-leaf terminals in each corner of the block (a total of 100 leaves) for beneficial mites. Take only one to two healthy, dark green fruit and one terminal per tree. Select trees that are three to four rows in from the outside edge of the block. Monitor as long as small (0.75 inch diameter or less) susceptible fruit is on the tree: for oranges, this is about 6 to 8 weeks in spring; for lemons, monitoring is necessary June through October. As fruit get larger, treatment thresholds go up.

When a treatment of sabadilla, spinosad, or abamectin is planned, beneficial mite populations are considered significant if you have more than 0.5 predators 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; 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. If an application of dimethoate, formetanate hydrochloride (Carzol), cyfluthrin (Baythroid), or fenpropathrin (Danitol) 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 blower wind velocity. Ground application is much 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.

Sabadilla, spinosad, or abamectin 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. Sabadilla, spinosad, and abamectin have a very short residual period so treatment timing (mid-hatch) is critical. Use the thresholds listed above to determine if a treatment is necessary.

Dimethoate, formetanate hydrochloride, cyfluthrin, and fenpropathrin 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.

Common name		Amount to Use	Minimum Days before Harvest+
(trade name)		(type of coverage)**
A.	SABADILLA
	(Veratran D)	10–20 lb/acre PLUS up to	24 hours
		10 lb sugar or 1.5 gal molasses
		in 50–200 gal (OC)
	RANGE OF ACTIVITY: Narrow (citrus thrips)
	PERSISTENCE: 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. Use higher rates with more dilute applications. Do not combine with fertilizers. 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.	SPINOSAD
	(Success) 2SC	4-6 fl oz/acre (OC)	1
	...OR...
	(Entrust) 80WP#	3 oz	1
	...PLUS...
	NARROW RANGE OIL#
	(415)	0.25%
	RANGE OF ACTIVITY: Narrow (citrus thrips, orangeworms, katydids)
	PERSISTENCE: Short
	COMMENTS: For use on all varieties. Most effective if substantial numbers of predators such as the predaceous mite Euseius tularensis are present. Spinosad is a short-residual material (8-24 hours); 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 spinosad more than 2 times/year, do not apply more than a total of 29 fl oz/acre/crop, and do not apply to citrus nurseries or to citrus in greenhouses.
C.	ABAMECTIN*
	(Agri-Mek) 0.15 EC	10 fl oz/acre (OC)	7
	...PLUS...
	NARROW RANGE OIL
	(415)	0.25%
	RANGE OF ACTIVITY: Narrow (citrus thrips, mites)
	PERSISTENCE: Short
	COMMENTS: For use on all varieties. Apply in 50–200 gal water/acre. Do not apply prebloom, during bloom, in nurseries, or on nonbearing trees. 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. Abamectin is a short residual material; 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. Apply no more than 2 applications of abamectin plus oil/season with a minimum of 30 days between treatments.
D.	CYFLUTHRIN*
	(Baythroid) 2E	6.4 fl oz/acre (OC)	12 hours
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Long
	RESISTANCE: In some citrus thrips populations in the San Joaquin Valley
	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. Do not apply within 25 feet of lakes, reservoirs, rivers, permanent streams, marshes, or natural ponds, estuaries, and commercial fish farm ponds.
E.	FENPROPATHRIN*
	(Danitol) 2.4 EC	21.33 fl oz/acre (OC)	1
	RANGE OF ACTIVITY: Broad (insects and mites)
	PERSISTENCE: Long
	RESISTANCE: In some citrus thrips populations in the San Joaquin Valley
	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. Do not apply in the vicinity of aquatic areas and do not apply more than 21.33 fl oz/acre/year.
F.	FORMETANATE HYDROCHLORIDE
	(Carzol) 92SP	1–1.25 lb/acre (OC)	See comments
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Long, unless washed off by rain,
	RESISTANCE: In some citrus thrips populations
	COMMENTS: For use on oranges, lemons, limes, tangerines, tangelos, and grapefruit. No more than 2 applications can be made/season with a minimum of 14 days between treatments. 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. Ground application at 3 mph with reduced wind velocity so as to achieve outside coverage.
G.	DIMETHOATE
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Long
	RESISTANCE: In some citrus thrips populations
	(Dimethoate 400) 4EC	1–2 qt/acre in 100–200 gal (OC)	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.
	...OR...
	(Dimethoate 2.67)	4–6 pt/acre in 100–200 gal (OC)	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.

**	OC - Outside coverage uses 50–500 gal/acre.
	A - Aircraft applications 5-20 gal/acre
+	Minimum days before harvest takes into account the California restricted entry interval and the federal preharvest interval and lists the longer interval. (See Table 1 Mandatory Intervals Between Application, Reentry and Harvest, and Hazards to Bees.)
*	Permit required from county agricultural commissioner for purchase or use.
#	Acceptable for use on organically grown produce.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Insects, Mites, and Snails
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O’Connell, UC Cooperative Extension, Tulare Co.
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura Co.
C. E. Kallsen, UC Cooperative Extension, Kern Co.
D. R. Haviland, UC Cooperative Extension, Kern Co.
Acknowledgments for contributions to the insect, mite, and snail section:
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
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA

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