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.
Damage
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.
Management
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, esfenvalerate, methomyl) for control of other pests, in order to conserve natural enemies of the leafminer.
Biological Control
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.
| Common name | Amount per acre** | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used. | ||||
| A. | ABAMECTIN | |||
| (Agri-Mek SC)* | 1.75–3.5 fl oz | 12 | 7 | |
| MODE-OF-ACTION GROUP NUMBER1: 6 | ||||
| COMMENTS: Do not apply at less than 7-day interval. Do not exceed 48 fl oz/acre per growing season. Do not apply in less than 20 gal water/acre. Do not make more than two sequential applications. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| B. | SPINETORAM | |||
| (Radiant SC) | 6–10 fl oz | 4 | 1 | |
| MODE-OF-ACTION GROUP NUMBER1: 5 | ||||
| COMMENTS: Is more efficacious and has longer residual activity than spinosad. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| C. | SPINOSAD | |||
| (Entrust)# | 2–3 oz | 4 | 1 | |
| (Success) | 6–10 oz | 4 | 1 | |
| MODE-OF-ACTION GROUP NUMBER1: 5 | ||||
| COMMENTS: Best control is achieved when aimed at newly hatched larvae and coverage is thorough. Can remain toxic to larval stages (especially syrphid fly) for 5 to 7 days after insecticide application. Do not exceed 29 fl oz of Success or 9 oz of Entrust/acre per crop. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| D. | CYROMAZINE | |||
| (Trigard WP) | 2.66 oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: 17 | ||||
| COMMENTS: Do not make more than two sequential applications. | ||||
| E. | AZADIRACHTIN# | |||
| (Neemix 4.5) | 4.0–7.0 fl oz | 4 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: un | ||||
| COMMENTS: Must be consumed by larvae; kills leafminer after pupation. A regulated product in an organically certified crop. | ||||
| ** | See label for dilution rates. |
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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 (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). |