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How to Manage Pests
UC Pest Management Guidelines
Citrus
Citrus Leafminer
Scientific Name: Phyllocnistis citrella
(Reviewed 12/06,
updated 12/06)
In this Guideline:
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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.
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.
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+ |
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| A. |
IMIDACLOPRID |
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(Admire Pro) |
7–14 oz/acre |
12 hours |
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(Admire) 2F |
16–32 oz/acre |
12 hours |
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RANGE OF ACTIVITY : Narrow (citricola and red scale, aphids, glassy-winged sharpshooter, vedalia beetle) |
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PERSISTENCE : Long |
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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. |
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| B. |
ABAMECTIN |
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(Agri-Mek) |
10 fl oz/acre (OC) |
7 days |
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...PLUS... |
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NARROW RANGE 415 OIL |
1% |
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RANGE OF ACTIVITY : Narrow (mites, citrus thrips, citrus leafminer) |
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PERSISTENCE : Short |
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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. |
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| C. |
ACETAMIPRID |
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(Assail) 70WP |
1.7–2.9 oz/acre |
7 days |
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RANGE OF ACTIVITY : Narrow (citricola scale, aphids, glassy-winged sharpshooter, vedalia beetle) |
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PERSISTENCE : Short |
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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. |
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| D. |
NARROW RANGE OIL |
1% |
4 hours |
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RANGE OF ACTIVITY : Broad |
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PERSISTENCE : Short |
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COMMENTS: Oils will
kill eggs laid on leaves, but have only a mildly suppressive effect on larvae. |
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| E. |
DIFLUBENZURON* |
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(Micromite) 80 WSG |
3.125 – 6.25 oz/acre (OC) |
21 days |
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...PLUS... |
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NARROW RANGE 415 OIL |
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RANGE OF ACTIVITY : Narrow (citrus peelminer, citrus leafminer, silver mite, katydids, grasshoppers) |
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PERSISTENCE : Short |
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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. |
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| F. |
AZADIRACHTIN |
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(Neemix 4.5) |
4 – 7 oz/acre (OC) |
12 hours |
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RANGE OF ACTIVITY : Narrow (larval stages of some insects) |
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PERSISTENCE : Short |
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COMMENTS: Short residual, requires repeated applications every 14-21 days. |
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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. OConnell, 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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