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UC Pest Management Guidelines

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Citrus

Cottony Cushion Scale

Scientific Name: Icerya purchasi

(Reviewed 7/03, updated 7/05)

In this Guideline:

Description of the pest
Damage
Management

DESCRIPTION OF THE PEST
The most distinguishing feature of the cottony cushion scale female is the fluted cottony egg sac that she secretes. About 600 to 800 eggs are laid in the sac. Hatching occurs within a few days in summer, but can take up to 2 months in winter. Newly hatched nymphs are red with dark legs and antennae. First and second instar feed on twigs and leaves, usually along the veins. Third instars and adults are found mainly on branches and the trunk, rarely the fruit. Third instars are covered with a thick, cottony secretion that disappears after they molt. Adult females settle and begin to form the white, elongated egg sac. Males are rare and females can reproduce without mating. There are three generations a year.

DAMAGE
Cottony cushion scales extract plant sap from leaves, twigs, and branches, thus reducing tree vigor. If infestations are heavy, leaf and fruit drop can occur along with twig dieback. The scale secretes honeydew, which promotes the growth of sooty mold.

MANAGEMENT
The cottony cushion scale was a major pest of citrus in the 1880s. Efforts at controlling this pest resulted in one of the earliest and most impressive examples of biological control. Today, infestations occur in the San Joaquin Valley because of the temporary destruction of the natural enemies by insecticide treatments such as pyrethroids, neonicotinoids, and insect growth regulators. If you encounter cottony cushion scale, look for its natural enemies. Insecticide treatments are usually not necessary unless the use of pyriproxyfen (Esteem) has decimated vedalia beetle populations.

Biological Control
Two natural enemies effectively control cottony cushion scale. The vedalia beetle, Rodolia cardinalis, was introduced from Australia in the early 1890s. The adult and larva feed on all stages of the scale. Female beetles lay eggs underneath the scale or attached to the egg sac. Young larvae move into the egg mass and feed on eggs. Later, larvae feed on all scale stages. For more information about the life cycle of the cottony cushion scale and the vedalia beetle, see UC ANR Publication 8051, Stages of Cottony Cushion Scale and its Natural Enemy, the Vedalia Beetle.

The parasitic fly, Cryptochaetum iceryae, was also introduced from Australia and is a very effective parasite of this scale in coastal areas. The fly deposits its eggs inside the scale body. Upon hatching, parasite larvae feed on the scale body and pupate within the remains of the scale. Control ants if they are tending cottony cushion scale because they can significantly disrupt natural enemy activity.

Cultural Control
If cottony cushion scale is a problem, pruning the interior of the canopy, especially in seldom-pruned old trees, to remove dead branches and crossing limbs, can help reduce an infestation. Also in young trees, pruning the lower scaffold area can help.

Organically Acceptable Methods
Biological and cultural control are acceptable for use on an organically certified crop.

Monitoring and Treatment Decisions
Monitor cottony cushion scale and its natural enemy the vedalia beetle. You may see red eggs or larvae of the vedalia beetle on the white egg sac of the scales or find its pupal cases attached to leaves. In the San Joaquin Valley, cottony cushion scale can become a serious problem in spring after use of broad-spectrum insecticides such as organophosphates, carbamates, and pyrethroids for citrus thrips and worm control. This is because these pesticides kill the vedalia beetle during the period when it is most actively feeding and reproducing on cottony cushion scale (March–June). The vedalia beetle will often recover from these sprays and control cottony cushion scale infestations by early summer. Of greater concern is the effect of insect growth regulators (IGRs) such as pyriproxyfen (Esteem) and buprofezin (Applaud) for California red scale control and neonicotinoids (imidacloprid-Provado and Admire and acetamiprid-Assail) for citricola scale and glassy-winged sharpshooter control. Insect growth regulators prevent vedalia beetle from completing pupation and emerging as adults; pyriproxyfen also prevents the beetle eggs from hatching. The neonicotinoids kill vedalia beetles when they contact the residues or feed on cottony cushion scale that have taken up the insecticide systemically. The residues from pyriproxyfen, buprofezin, and imidacloprid can last more than 5 months. A sign that IGRs are killing vedalia beetles is the presence of dead vedalia beetle pupae on the outside leaves of trees. IGRs will also kill the cottony cushion scale pest, but they kill it very slowly. The orchards that experience the worst cottony cushion problems are not the orchards that are sprayed with IGRs, because the IGRs kill the cottony cushion scale as well as the California red scale. The worst cottony cushion scale outbreaks are in neighboring orchards because the spray drift from the treated orchard kills the vedalia beetle but not the cottony cushion scale. The neonicotinoids do not have any effect on cottony cushion scale.

The vedalia beetle is the best method of controlling cottony cushion scale. Vedalia beetles grow very rapidly: they can complete four generations in the time it takes cottony cushion scale to complete one generation. They consume huge numbers of cottony cushion scale eggs and nymphs in a very short amount of time. When vedalia beetles arrive in an orchard, they can control a serious cottony cushion scale problem in 4 to 6 weeks. Insecticides are often not as effective as vedalia beetle and are disruptive to the natural enemies needed for California red scale control. However, organophosphate treatments may be warranted if the IGRs have temporarily eliminated the vedalia beetle throughout the San Joaquin Valley.

In coastal areas, the parasitic fly can usually be observed parasitizing cottony cushion scales. The emerging parasite leaves an exit hole in the mummified scales. Ants are attracted to the honeydew excreted by this scale but do not interfere greatly with its biological control.

Common name		Amount to Use	Minimum Days before Harvest+
(trade name)		(type of coverage)**

A.	VEDALIA BEETLES#
	RANGE OF ACTIVITY: Narrow (cottony cushion scale)
	PERSISTENCE: Intermediate (as long as cottony cushion scale are present)
	COMMENTS: No commercial insectaries are currently rearing vedalia beetles; finding them in one orchard and moving them to another is the best method of establishing vedalia in an orchard. During Feb.-April, simply collect vedalia adults, pupae, or any stages that you can find, and move them into the problem orchard. Place the vedalia on top of a cottony cushion scale infestation in the branches of a tree in several trees in the orchard; they should spread on their own from there. If the conditions are right, one early release of 25 vedalia individuals/10 acre block should be sufficient, but more is always better. They can be moved into a cottony cushion-infested orchard any time of the year, but they seem to do their best in early spring, especially when the population of cottony cushion scale consists mostly of very large female scale, which is the preferred stage for feeding and egg-laying. When the vedalia beetle consumes all of the cottony cushion scale, it will fly away in search of more food.

B.	BUPROFEZIN
	(Applaud) 70DF	2.14–2.86 lb/acre (TC)	3
	(Applaud) 70W	2.1–2.84 lb/acre (TC)	60
	RANGE OF ACTIVITY: Narrow (California red scale, whiteflies, vedalia beetle)
	PERSISTENCE: long (2–3 months)
	COMMENTS: Insect growth regulator; works best for low-to-moderate populations. For use on all varieties. Toxic to vedalia beetles. Most effective if applied after peak emergence of the first generation of crawlers. Apply after the crawlers have settled down and formed white caps. Slow-acting; This product does not kill the scale until they molt, so decline of the population is usually not observed until the next generation. No more than 2 applications/season and allow 60 days between applications.

C.	MALATHION 8 Spray	1–2 pt/100 gal (TC)	7
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Intermediate
	COMMENTS: For use on all varieties. Do not apply during bloom period.

D.	METHIDATHION*
	(Supracide) 25WP	0.5 lb/100 gal (TC)	14
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Long
	Resistance: Some California red scale and yellow scale populations in the San Joaquin Valley.
	COMMENTS: For use on all varieties. Do not apply during bloom or exceed 40 lb/acre/season or 2 applications/fruit year, 45 days apart for dilute (TC). May increase citrus red mite populations.

E.	CARBARYL*
	(Sevin) 80S	1–1.2 lb/100 gal (TC)	5
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Long
	Resistance: Some California red scale and some Euseius tularensis populations in the San Joaquin Valley.
	COMMENTS: For use on all varieties. Do not apply during bloom or exceed 25 lb/acre/application. May increase citrus red mite populations.

**	TC - Thorough coverage uses 1,000–3,000 gal water or more/acre, depending on tree size.
+	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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