How to Manage Pests

UC Pest Management Guidelines

DAMAGE
Citricola scale can be a serious pest of citrus in the San Joaquin Valley. A severe infestation may reduce tree vigor, kill twigs, and reduce flowering and fruit set. As they feed, citricola scale excrete honeydew, which accumulates on leaves and fruit. Sooty mold grows on honeydew and interferes with photosynthesis in leaves and causes fruit to be downgraded in quality during packing.

MANAGEMENT
Citricola scale is completely controlled by Metaphycus parasites in southern California and is rarely seen. Even though these parasites are established in the San Joaquin Valley, biological control is not effective there, and treatments may be necessary in groves where broad-spectrum pesticides are not regularly used to control other pests. In groves practicing biologically based pest management (e.g., releasing Aphytis melinus for California red scale control), growers may consider withholding broad-spectrum citricola sprays until Aphytis activity is over in the fall (e.g., late October or November).

Biological Control
Introduced and indigenous parasitic wasps, Metaphycus stanleyi, M. helvolus, and M. luteolus, control citricola scale in southern California. The latter two parasites occur in the San Joaquin Valley (along with Coccophagus lycimnia) but are unable to control citricola scale there. Controlling ants will help improve biological control.

Organically Acceptable Methods
Biological control and petroleum oil sprays are acceptable for use in organically managed orchards.

Selectivity
Oil is the most selective pesticide available for control of citricola scale. However, oil simply reduces the scales' overall numbers and in many cases must be applied every year. Chlorpyrifos (Lorsban) is less selective, however, a low rate (1–2 pt/acre) can more effectively reduce citricola scale than oil, and a full scale rate of Lorsban (6–12 pt/acre) can suppress densities so effectively that another spray is not needed for 3 to 5 years. The systemic neonicotinoid imidacloprid (Admire) is fairly selective and moderately effective in controlling citricola scale. The neonicotinoids imidacloprid (Provado) and acetamiprid (Assail) are the least selective insecticides. However, they have shorter REI and PHI intervals, and they are more effective in the spring months than chlorpyrifos. The neonicotinoids should not be used in cottony cushion scale-infested orchards because they have no effect on cottony cushion scale, but they are highly toxic to the predatory vedalia beetle.

Monitoring and Treatment Decisions
Citricola scale is very sensitive to organophosphates and carbamates and generally does not become a problem until growers stop using these insecticides for other pests. Check for citricola scale at all times of the year when monitoring for other scales, but look especially closely at the twigs and leaves in January–March and at the underside of leaves in mid- to late August.

Be sure to distinguish the citricola scale from brown soft scale. Brown soft scale has multiple generations and so all stages will be present on leaves, whereas citricola scale has only one generation and the nymphs will be uniform in size (for details see UC ANR Publication 3303, IPM for Citrus, 2nd edition).

January-March Sampling.First look to see if the population is primarily on the twigs or leaves. There are no established treatment thresholds for adults on twigs in spring. However, if high populations are observed (more than 5 live adult scale on a twig with 10 leaves), the orchard may require a treatment before bloom. If the adults have not moved back on the twigs and are still found on the leaves and there are an average of more than 0.5 scale insects per leaf, then the orchard requires treatment. If the population on twigs or leaves is observable but lower, then it is best to postpone treatments until fall when scales are small, positioned on leaves on the outside of the tree, and generally easier to control.

August Sampling. To sample for citricola scale in August, walk down four evenly spaced rows of the block. In each row, pick one leaf from the northeast corner of 25 trees. Examine the scale on the underside of the leaf to determine if they are alive or dead. Count the number of leaves in the 25-leaf sample that are infested with live scale (presence-absence sampling). A treatment is warranted if one or more of the four rows has 13 or more leaves infested with live citricola scale in a 25-leaf sample. If 5 to 12 leaves are infested, the population is building and should be watched very closely. If four or fewer leaves are infested, then a treatment is not needed this season. Apply fall treatments after egg hatch is complete, the adult females have died, the nymphs have moved on the leaves (generally mid-August), and the temperatures are still warm (up to early October). Because citricola scale are very sensitive to organophosphates and carbamates, rates that are lower than that recommended for armored scale can be very effective. Lower rates (2–6 pt chlorpyrifos [Lorsban]/acre) and delays in treatment until late October are suggested when parasites of California red scale need to be preserved. However, lower rates may result in a shorter period of control (1 year). Higher rates (6–12 pt chlorpyrifos [Lorsban]/acre) or application earlier in the season (mid-August through early October) are recommended if the population of citricola scale is very high or if California red scale must be controlled simultaneously. Citricola scale populations grow more rapidly and survive the summer better when the San Joaquin Valley experiences a cool, wet spring. When these conditions occur, the higher rates and earlier applications (mid-August through September) are more effective and may be necessary to stop honeydew production.

Common name		Amount to Use	Minimum Days before Harvest+
(trade name)		(type of coverage)**
LIGHT TO MODERATE INFESTATION ONLY
A.	NARROW RANGE OIL#
	(415, 440)	1.2–1.4 gal/100 gal (TC)	4 hours
	RANGE OF ACTIVITY: Broad (unprotected stages of insects and mites)
	PERSISTENCE: Short
	COMMENTS: For use on grapefruit, lemons, navels, Valencias. Use higher rate for July or August applications only. To avoid phytotoxicity, use same treatment timings as given for oil sprays for California red scale in central California. Do not apply oil until hatch is complete (late July to early August). Caution: Serious hazards are associated with oil treatments to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
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 (scales, whiteflies, vedalia beetle)
	PERSISTENCE: Long (2–3 months)
	COMMENTS: 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.
MODERATE TO HEAVY INFESTATIONS
A.	CHLORPYRIFOS*
	(Lorsban) 4EC	Prebloom: 1 pt/100 gal (TC)	See comments below
		Prebloom: 5–7 pt/acre (LV)
		Late summer: 2–6 pt/acre (LV)
	RANGE OF ACTIVITY: Broad (insects and beneficial mites). More selective if used at lower rates, but also less efficacious.
	PERSISTENCE: Intermediate
	COMMENTS: For use on all varieties. In the prebloom period, use 1 pt/100 gal in 500 to 1,000 gal/acre; when using the low-volume treatment at this time, thorough coverage is essential. During late summer use 1.5 pt in 100 gal/acre (LV). Minimum days before harvest are 21 days for up to 7 pt/acre and 35 days above 7 pt/acre. Do not apply during Dec., Jan., or Feb. See label for additional restrictions.
B.	IMIDACLOPRID
	(Admire) 2F	32 fl oz/acre	12 hours
	RANGE OF ACTIVITY: Narrow (armored scale, citricola scale, aphids, glassy-winged sharpshooter, and vedalia beetle)
	PERSISTENCE: Long
	RESISTANCE: None
	COMMENTS: Apply to soil; remains effective 4–5 months. Moderately effective against nymphs and adults. Pre-wet soil before treatment is applied. Very toxic to bees; do not apply during bloom because bees may be drawn to irrigation water. For optimum uptake, apply to newly planted trees or trees irrigated by drip/ microsprinkler/low-pressure irrigation systems. Emitters must provide even, uniform distribution of water. Lightly pre-wet soil for several hours before application to break soil surface tension. Once the irrigation system reaches operating pressure, inject the treatment into the system over a calculated time interval (generally 2 hours) to allow uniform distribution throughout the system. The use of a dye marker in the treatment solution is recommended to determine when lines are clear of the treatment. Once the solution has cleared all irrigation lines and emitters, continue irrigation to move the insecticide into the active root zone but do not overirrigate or cause runoff. Wait 24 hours before subsequent irrigations. Apply in citrus orchards May–July. Toxic to vedalia beetle and should not be used in cottony cushion scale-infested orchards.
C.	IMIDACLOPRID
	(Provado) 1.6 F	10–20 oz/acre	12 hours
	RANGE OF ACTIVITY: Narrow (citricola scale, aphids, glassy-winged sharpshooter and vedalia beetle)
	PERSISTENCE: Intermediate
	RESISTANCE: None
	COMMENTS: Toxic to vedalia beetle; should not be used in cottony cushion scale-infested orchards. Apply in 300-1000 gal water/acre; use higher volume if insects are inside the canopy on the wood. Thorough coverage of foliage is necessary for optimal control. do not apply during bloom or within 10 days before bloom. Do not exceed 20 fl oz/acre/application or apply more than 40 fl oz/acre/year.
D.	ACETAMIPRID
	(Assail) 70 WP	3.4–5.7 oz/acre	7 days
	RANGE OF ACTIVITY: Narrow (citricola scale, aphids, glassy-winged sharpshooter and vedalia beetle)
	PERSISTENCE: Intermediate
	RESISTANCE: None
	COMMENTS: Residues last for 4–6 weeks. Apply in 300-1000 gal water/acre; use higher volume if insects are inside the canopy on the wood. Do not exceed 12.5 oz product/acre/season. Toxic to bees exposed to direct treatment; apply only during late evening, night, or early morning. Toxic to vedalia beetle and should not be used in cottony cushion scale-infested orchards. Use allowed under a 2(ee) recommendation.
E.	METHIDATHION*
	(Supracide) 25WP	1 lb/100 gal (TC)	14
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Long
	COMMENTS: For use on all varieties. Apply after bloom or at least 14 days before harvest. No more than 2 applications/year at least 45 days apart.
F.	MALATHION 8 Spray	1–2 pt/100 gal (TC)	7
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Short
	COMMENTS: For use on all varieties. Do not apply during bloom.
G.	CARBARYL*
	(Sevin) 80S	0.4 lb/100 gal (TC)	5
	ŸPLUSŸ
	NARROW RANGE OIL	0.5–1.4 gal/100 gal
	RANGE OF ACTIVITY: Broad (insects and beneficial mites)
	PERSISTENCE: Long
**	TC - Thorough coverage uses 1,000–3,000 gal water or more/acre, depending on tree size.
	LV - Low-volume uses 20–100 gal water/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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