How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Citrus leafminer is a very small, light colored moth that arrived in southern California from Mexico in 2000. Citrus leafminer has been moving northward in backyard and commercial citrus since that time and now infests citrus in southern and central California.

Adult citrus leafminers are tiny moths about 2 mm long (less than 0.12 inch) with a wingspan of about 4 mm (or about 0.25 inch). They have silvery and white iridescent forewings with brown and white markings and a distinct black spot on each wing tip. Moths are most active from dusk to early morning and spend the day resting on the undersides of leaves, but are rarely observed. Soon after emerging from the pupal case, the female emits a sex pheromone that attracts males. Females lay eggs singly on the underside of leaves. Newly emerged leaflets (flush), particularly along the midvein, are the preferred oviposition site.

Eggs hatch about 4-5 days after being laid and newly hatched larvae begin feeding immediately in shallow, meandering mines in the leaves. As a larva increases in size, the mine becomes more visible and larval excrement forms a thin, central frass trail within the mine. Larvae molt 4 times over a 1 to 3 week period. Mature larvae pupate within the mine, rolling the edge of the leaf and protecting the pupa with silk. The entire life cycle of the insect takes 2 to 7 weeks to complete, depending on temperature and weather conditions. The activities of citrus leafminer vary somewhat with location in the state because of differences in climatic conditions and flushing of citrus trees. In general, citrus leafminer is active from mid-summer through fall and early winter.

DAMAGE

Citrus leafminer larvae feed by creating shallow tunnels, referred to as mines, in young leaves. It is most commonly found on citrus (oranges, mandarins, lemons, limes, grapefruit and other varieties) and closely related plants (kumquat and calamondin). The larvae mine the lower or upper surface of the leaves causing them to curl and look distorted. Mature citrus trees (more than 4 years old) generally tolerate leaf damage without any effect on tree growth or fruit yield. Citrus leafminer is likely to cause damage in nurseries and new plantings because the growth of young trees is retarded by leafminer infestations. However, even when infestations of citrus leafminer are heavy on young trees, trees are unlikely to die.

In Florida, citrus leafminer creates openings that allow for entry of citrus bacterial canker into the tree resulting in infection. Citrus bacterial canker is not found in California. Annual surveys for citrus bacterial canker are conducted by the State of California, and other regulations are in place to exclude its introduction.

MANAGEMENT

Mature Citrus Orchards (more than 4 years old). While the new flush of mature trees may be heavily damaged by citrus leafminer and look unsightly, yield and tree growth will be unaffected. Therefore, insecticide treatments are generally not needed for mature citrus orchards. Worldwide, citrus leafminer populations are fairly well-controlled by parasitic wasps. However, citrus leafminer has only recently entered the state of California and parasites are not uniformly present or active in all regions where citrus leafminer has recently established. Do not spray citrus with broad-spectrum insecticides and avoid other practices that disrupt natural enemies whenever possible to encourage natural enemies. Citrus peelminer and leafminer share many of the same parasites including Cirrospilus and Pnigalio species.

Young Citrus Orchards (less than 4 years old). Because citrus leafminer can retard the growth of young trees, apply insecticides to nursery citrus trees and new plantings of citrus. Imidacloprid (Admire) applied through the irrigation for young trees or to the soil of potted citrus provides the longest period of control (1 to 3 months). The length of control depends on tree spacing and soil and irrigation conditions. Time applications of Admire to protect periods of flushing.

Foliar insecticides suppress citrus leafminer for shorter periods of time (several weeks) compared to Admire. Foliar treatments are effective for only 2 to 3 weeks because citrus leafminer adults lay eggs on new flush growth that was not present at the time of treatment. Oil has been shown to work as a temporary oviposition deterrent in nursery settings but should be used with care to avoid phytotoxicity. Diflubenzuron (Micromite) is effective primarily against eggs and larval stages.

Cultural Control
Citrus leafminer moths are attracted to new flush of citrus trees. Avoid pruning live branches more than once a year, so that the cycles of flushing are uniform and short. Once the leaves harden, the pest will not be able to mine the leaves. Do not prune off leaves damaged by citrus leafminer because undamaged areas of the leaves continue to produce food for the tree. Do not apply nitrogen fertilizer at times of the year when leafminer populations are high and flush growth will be severely damaged.

Vigorous shoots known as water sprouts often develop on branches and above the graft union on the trunk of mature trees. These shoots grow rapidly and produce new leaves for a prolonged period of time. Where citrus leafminer is a problem, remove water sprouts that might act as a site for the moths to lay eggs (oviposition). Always remove suckers, the vigorous shoots that grow from the trunk below the graft union, because they originate from the rootstock and do not produce desirable fruit.

Monitoring
Traps baited with a pheromone (insect sex attractant) are available for citrus leafminer and are a useful tool for determining when moths are flying and depositing eggs. Hang a trap containing the pheromone inside a citrus tree at about chest height during March through November. Follow the manufacturer's recommendations for maintaining the trap, such as the frequency with which pheromones should be replaced. Use one pheromone trap per 5 acres. Check the traps weekly for moths. Citrus leafminer moths may be captured in traps almost any time during the growing season. However, this species is most abundant when citrus is flushing in the summer and fall months. These traps will help you determine when male flights are occurring and when to time insecticide applications if they are needed. Ovicides such as oil or diflubenzuron (Micromite) should be applied during peak flights of moths.

Common name		Amount to Use	Minimum Days before Harvest+
(trade name)
A.	IMIDACLOPRID
	(Admire Pro)	7–14 oz/acre	12 hours
	(Admire) 2F	16–32 oz/acre	12 hours
	RANGE OF ACTIVITY : Narrow (citricola and red scale, aphids, glassy-winged sharpshooter, vedalia beetle)
	PERSISTENCE : Long
	COMMENTS: An important treatment for nurseries and the first two years after citrus is planted. Apply to soil; remains effective 1 to 3 months. Moderately effective against mining larvae. Requires 3 to 4 weeks for uptake into mature citrus and less in smaller trees. 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 1 month before trees begin to flush. Allows most natural enemies to survive, except vedalia beetles. Do not use where cottony cushion scale is a problem.
B.	ABAMECTIN
	(Agri-Mek)	10 fl oz/acre (OC)	7 days
	...PLUS...
	NARROW RANGE 415 OIL	1%
	RANGE OF ACTIVITY : Narrow (mites, citrus thrips, citrus leafminer)
	PERSISTENCE : Short
	Comments: 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%. Use ground application at 3 mph with reduced wind velocity so as to achieve outside coverage. Apply no more than 1 application of abamectin plus oil/season.
C.	ACETAMIPRID
	(Assail) 70WP	1.7–2.9 oz/acre	7 days
	RANGE OF ACTIVITY : Narrow (citricola scale, aphids, glassy-winged sharpshooter, vedalia beetle)
	PERSISTENCE : Short
	COMMENTS: Can be used on nusery stock for commercial plantings. Repeat applications of any neonicotinoid insecticides (acetamiprid-Assail: imidacloprid-Admire, Provado) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action Group number to help delay the development of resistance.
D.	NARROW RANGE OIL	1%	4 hours
	RANGE OF ACTIVITY : Broad
	PERSISTENCE : Short
	COMMENTS: Oils will kill eggs laid on leaves, but have only a mildly suppressive effect on larvae.
E.	DIFLUBENZURON*
	(Micromite) 80 WSG	3.125 – 6.25 oz/acre (OC)	21 days
	...PLUS...
	NARROW RANGE 415 OIL
	RANGE OF ACTIVITY : Narrow (citrus peelminer, citrus leafminer, silver mite, katydids, grasshoppers)
	PERSISTENCE : Short
	COMMENTS: Can be used during bloom. Timing treatments for peaks in moth flights is important because Micromite is effective primarily against the egg stage of the leafminer. There is a limit of 6.25 oz per 90 day period or 18.75 oz per year. Do not apply within 25 feet of bodies of water. Suppresses citrus leafminer for several weeks.
F.	AZADIRACHTIN
	(Neemix 4.5)	4 – 7 oz/acre (OC)	12 hours
	RANGE OF ACTIVITY : Narrow (larval stages of some insects)
	PERSISTENCE : Short
	COMMENTS: Short residual, requires repeated applications every 14-21 days.
+	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.

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
K. Godfrey, USDA Biological Control, Sacramento
D. Headrick, California Polytechnic State University, San Luis Obispo
B. Faber, UC Cooperative Extension, Ventura Co.
J. Kabashima, UC Cooperative Extension, South Coast Research and Extension Center

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