How to Manage Pests
UC Pest Management Guidelines
Liriomyza huidobrensis, L. sativae, and L. trifolii
In this Guideline:
Adults are small black to gray flies with yellow
markings. Females puncture leaves to feed on plant sap and lay eggs within the
leaf tissues. After 2 to 4 days, eggs hatch. Larvae feed between the upper and
lower surface of the leaves, making distinctive winding, whitish tunnels or
mines that are often the first clue that leafminers are present. Larvae emerge from the mines and pupate on the leaf surface or, more commonly, in
cracks in the soil. Many generations occur each year and the entire life cycle
can be completed in less than 3 weeks when the weather is warm.
Adult leafminers have such a preference for cotyledons that seedling
growth may be stunted. Larvae mine between upper and lower leaf surfaces,
creating winding, whitish tunnels that are initially narrow, but then widen as
the larvae grow. Excessive mining renders leaves unmarketable, reduces
photosynthetic capacity, and provides easy access for disease organisms.
Natural enemies, especially parasitic wasps in the genus Diglyphus, commonly reduce populations of
leafminers, unless killed off by insecticides applied to control other pests.
To avoid killing beneficials, choose selective pesticides for treating other
pests, whenever possible. Other parasites attack leafminers, but because
leafminers feed within the leaf, they are protected from most predators.
attack a wide variety of vegetable crops often grown in proximity to spinach.
Where possible, avoid planting next to infested fields, especially those near
harvest. Postharvest disking of fields destroys pupae and reduces migration of
adult flies into susceptible fields.
Biological and cultural controls and sprays of azadirachtin
(AZA-Direct, Neemix) are acceptable for use on organically grown produce.
Monitoring and Treatment Decisions
Regularly check young seedlings for leaf mines. Most mines occur on
cotyledons and the first true leaves. Some mines are most obvious from the
underside of the leaf. If leafminer populations build to high levels when
seedlings have 4 to 5 leaves, a chemical treatment may be necessary. Treat if
you find more than an average of one mine per leaf in your overall field
sample. To be effective, sprays must be applied to the larval stage.
|The following materials are listed in order
of usefulness in an IPM
program, taking into account efficacy, information related to natural
enemies and honey bees, and
environmental impact. Not all registered pesticides are listed. Always read
label of product being used.
||MODE OF ACTION GROUP NUMBER1: 17
||COMMENTS: Very effective against leafminer larvae. Do not make
more than 2 sequential applications. Check label for plantback restrictions.
||MODE OF ACTION GROUP NUMBER1: 18B
||COMMENTS: This material is consumed by the larvae but does not
kill the leafminer until it finishes feeding, drops from the plant, and forms
a pupa; consequently it doesn't prevent damage from current generation but it
can prevent the production of a following generation. Kills leafminer after
pupation. In an organically certified crop, check with certifier for restrictions regarding the use of this product.
UC IPM Pest Management Guidelines: Spinach
UC ANR Publication 3467
Insects and Mites
S. T. Koike, UC Cooperative Extension, Monterey County
M. LeStrange, UC Cooperative Extension, Tulare County
Acknowledgements for contributions to Insects and Mites:
W. E. Chaney, UC Cooperative Extension, Monterey County
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