How to Manage Pests
UC Pest Management Guidelines
Scientific name: Liriomyza trifolii
(Reviewed 12/09, updated 11/12)
In this Guideline:
DESCRIPTION OF THE PEST
Liriomyzid leafminer adults are small, shiny black flies with a bright yellow triangular spot on the upper thorax. Eggs are white and oval and laid within the leaf. Larvae feed between leaf surfaces, creating meandering tracks or mines. Mature larvae leave the mine and drop to the ground to pupate. The life cycle takes only 2 weeks in warm weather; there can be many generations a year.
Larvae mine between upper and lower leaf surfaces, creating winding, whitish tunnels that are initially narrow, but then widen as the larvae grow. Leaves injured by leafminers drop prematurely; heavily infested plants may lose most of their leaves.
Leafminers are rarely a problem in the Imperial Valley. In other areas, regular monitoring for leaf mines is important in detecting damaging populations of this pest. Avoid the use of early-season applications of broad-spectrum insecticides (dimethoate, endosulfan, esfenvalerate, methomyl) for control of other pests, in order to conserve natural enemies of the leafminer.
Natural enemies, primarily parasitic wasps in the Diglyphus genus, often control leafminers. When parasites are killed by pesticides, leafminer outbreaks are common.
Organically Acceptable Methods
Biological control and sprays of azadirachtin and the Entrust formulation of spinosad are acceptable for use on organically certified produce.
Monitoring and Treatment Decisions
Regularly check leaves for leaf mines, especially between bloom and fruit development. Most mines occur on older bottom leaves and some mines are most obvious from the underside of the leaf. Also look for dead larvae, which is a sign of parasitism. If parasitism levels are at least 50%, the crop will most likely tolerate damage. However, if leafminer populations build up to high levels, a chemical treatment may be necessary. Avoid early-season applications of broad-spectrum insecticides for other insects, because they may cause leafminer outbreaks to occur.
UC IPM Pest Management Guidelines:
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County