How to Manage Pests
UC Pest Management Guidelines
Onion and Garlic
Leafminers
Scientific name: Liriomyza spp.
(Reviewed 1/07,
updated 1/07)
In this Guideline:
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Adults are small black and yellow flies. Females puncture the leaf
to feed on plant sap and to lay eggs within the leaf tissue. Eggs hatch within
2 to 4 days and the small white to yellow larvae tunnel within the leaf tissue.
Larger larvae may feed inside the hollow leaves of onions or garlic, but still
produce the characteristic "mines" visible from the outside of the
leaf. Larvae exit the leaf upon completion of their development and pupate in
the soil or in the leaf axils on plants. Many generations occur each year.
Damage caused by leafminers is primarily cosmetic in green bunching
onions; contamination by pupae and larvae, however, is a problem. Damage in dry
onions and garlic is of little concern unless populations become so high as to
prematurely kill foliage.
Biological Control
Natural enemies, especially parasitic wasps,
are commonly found reducing leafminer numbers. These parasitic wasps are very
susceptible to insecticide sprays, however, and may not be important in fields
where insecticides have been used.
Cultural Control
Leafminers attack a wide variety of crops in coastal California. Close
proximity to crops such as lettuce, celery, or spinach will increase the
potential for damage by leafminers in onions. It is also important that fields
being planted to onions that were previously in one of these susceptible crops
be worked thoroughly and that sufficient time be allowed to pass before
planting into these fields to allow pupae in the soil to emerge.
Organically Acceptable Methods
Biological controls are often effective in controlling this pest in
organically grown onion and garlic crops. Supplemental or inundative releases
of parasites are rarely economically justified. Cultural controls as described
above are critical. Neem products are allowed as restricted use materials.
Monitoring and Management Decisions
There is no established threshold for leafminer in onions. Because
large populations of adults do not always lead to large larval populations,
make your management decisions based on the level of larval infestations on the
plants.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
|
| |
| The following materials are listed
in order of usefulness in an IPM program, taking into account impact on natural enemies
and honey bees. When
choosing a pesticide, also consider information relating to environmental
impact.
|
| |
| A. |
CYROMAZINE |
| |
(Trigard) |
2.66 oz |
12 |
7 |
| |
MODE OF ACTION: A triazine (Group 17)1
insecticide.
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COMMENTS: For use on onion and garlic. Do not make more than 6 applications/crop. |
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| B. |
PERMETHRIN* |
|
12 |
1 |
| |
(Ambush) |
6.4–12.8 oz |
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MODE OF ACTION: A pyrethroid (Group 3)1
insecticide.
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COMMENTS: For use on garlic. Do not apply
more than 2 lb a.i./acre/season. May cause secondary outbreaks of spider mites. |
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| C. |
CYPERMETHRIN* |
| |
(Ammo 2.5 EC) |
2–5 oz |
12 |
7 |
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COMMENTS: For use on garlic. May cause secondary outbreaks of spider mites. |
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| D. |
PYRETHRIN and ROTENONE |
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(Pyrellin EC) |
1–2 pt |
12 |
0 |
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MODE OF ACTION: A botanical (Group 3)1
insecticide.
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COMMENTS: For use on garlic. This material
is helpful in reducing adult pressure when heavy migrations into the field are occurring. |
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| E. |
AZADIRACHTIN# |
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(Neemix) |
Label rates |
12 |
0 |
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MODE OF ACTION: A botanical/insect growth
regulator (Group 26)1 insecticide.
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COMMENTS: For use on garlic. A restricted use material in an organically certified crop. |
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UC IPM Pest Management Guidelines: Onion and Garlic
UC ANR Publication 3453
Insects and Mites
R. L. Coviello, UC Cooperative Extension, Fresno Co.
W. E. Chaney, UC Cooperative Extension, Monterey Co.
S. Orloff, UC Cooperative Extension, Siskiyou Co.
G. J. Poole, UC Cooperative Extension, Los Angeles Co.
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