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How to Manage Pests

UC Pest Management Guidelines


Adult vegetable leafminer.

Cole Crops

Leafminers

Scientific Name: Liriomyza spp.

(Reviewed 6/07, updated 9/09)

In this Guideline:


DESCRIPTION OF THE PESTS

Adults are tiny black flies with a bright yellow spot on their thorax. Females puncture leaves to feed on plant sap and lay eggs within the leaf tissues. After 2 to 4 days the eggs hatch and larvae feed between the upper and lower surface of leaves, making the distinctive winding, whitish tunnels or leafmines that may be the first clue to the leafminers' presence. Larvae emerge from the leafmines and pupate on the leaf surface or, more commonly, in cracks in the soil. Many generations may occur each year, and the entire life cycle can be completed in less than 3 weeks when the weather is warm.

DAMAGE

Leafminers can reduce the plant's photosynthetic capacity, render edible leaf portions unmarketable, and provide an entrance for pathogenic organisms.

MANAGEMENT

Leafminers are primarily seedling pests. Natural enemies, especially parasitic wasps in the Diglyphus genus, commonly control leafminers, unless killed off by insecticides applied to control other pests. Choose selective pesticides for treating other seedling pests to avoid this problem. Regular monitoring during the seedling start will help determine the need for treatment.

Liriomyzid leafminers attack a wide variety of vegetable crops often grown in proximity to cole crops. Where possible avoid planting next to infested fields, especially those near harvest.

Organically Acceptable Methods
The Entrust formulation of spinosad is acceptable for use on organically certified produce.

Monitoring and Treatment Decisions
Regularly check young seedlings for leafmines. Most mines occur on the cotyledons and first true leaves. If leafminer populations build to high levels when seedlings have only four or five leaves, chemical treatment may be necessary. Treat if you find an average of one or more mines per leaf in your overall field samples. Broccoli or cauliflower with six or more leaves are rarely damaged by leafminers, regardless of population numbers. However, for cabbage or lettuce, if edible leaves are mined, chemical control may be justified.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to natural enemies and honey bees as well as the environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. CYROMAZINE
  (Trigard) WP 2.66 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 17
  COMMENTS: For Chinese cabbage and Chinese mustard. Do not apply more than 1 lb of product/acre/season.
 
B. SPINETORAM
  (Radiant) SC 5–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Toxic against some natural enemies (predatory thrips, syrphid fly larva, beetles) when sprayed and 5 to 7 days after. Control improved with addition of an adjuvant.
 
C. SPINOSAD
  (Entrust)# 1.25–3 oz 4 1
  (Success) 4–10 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Toxic against some natural enemies (predatory thrips, syrphid fly larva, beetles) when sprayed and 5 to 7 days after. Use higher rate for heavy infestations.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cole Crops
UC ANR Publication 3442
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgments for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
W. E. Chaney, UC Cooperative Extension, Monterey County
N. C. Toscano, Entomology, UC Riverside

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