Description of the Pest
Vinegar flies, also known as fruit or pomace flies, are small, yellowish flies that are commonly attracted to fermenting fruit of all kinds. Vinegar fly numbers may increase as the freezer harvest season progresses and temperatures become warmer, especially in Southern California. The 0.15 inch (4 mm) larva can be found in very ripe cull and damaged fruit in the fields. Adults lay 700 to 800 eggs in a life span that ranges from 7 to 8 days in summer to 20 to 30 days at other times. Ideal temperatures for development of this insect are in the low 80°F (27° to 30°C). The flies do not lay eggs at temperatures below 54°F (12°C) or above 91°F (33°C).
Damage
Vinegar flies are primarily a problem in strawberries picked for freezing. Because this fruit is allowed to ripen in the field to allow easy removal of the calyx and core of the strawberry during picking, the harvest interval is increased and the fruit becomes more susceptible to infestation. Vinegar flies are attracted to very ripe or damaged fruit in the field where they lay their eggs. Eggs and larvae are primarily a contamination problem.
Management
When conditions favor an increase in vinegar fly numbers, remove as much overripe fruit from the field as possible, or bury it, and follow good sanitation practices in areas around the field. Monitor vinegar flies with bait traps to help detect infestations as early as possible.
Cultural Control
- Limit fruit fly breeding sites.
- Completely remove ripe fruit from the plants.
- When possible, shorten harvest intervals as temperatures increase.
- Practice good sanitation in and around the field. Identify and clean up external sources of flies (e.g., cull piles of strawberries or other rotting fruit and nearby citrus groves where old fruit may be on the ground).
Organically Acceptable Methods
Use cultural controls, especially field sanitation, and pyrethrin sprays on organically certified strawberries.
Monitoring and Treatment Decisions
Although no monitoring or treatment guidelines exist for vinegar flies in strawberries, adult flies may also be monitored using fermented fruit traps consisting of a container filled with overripe fruit covered with an inverted funnel. High numbers of vinegar flies are found in May and June in Southern California, so start checking for flies at the end of April in these areas. It may be possible to spray portions of fields or obvious sources of flies with pyrethrins to control adult flies.
Vinegar fly eggs and larvae in the berries cannot be killed using insecticides. Apply sprays to target adult flies. Adult flies are most active in the early morning and late afternoon; this is also the time they will have greater exposure to an insecticide application. Best time to apply insecticide for adults is between 8 and 11 a.m. and between 5 and 7 p.m.
| 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. | MALATHION | |||
| (Malathion 5EC) | 1.5–3 pt | 12 | 3 | |
| MODE-OF-ACTION GROUP NUMBER1: 1B | ||||
| COMMENTS: Provides effective control. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| B. | PYRETHRIN# | |||
| (PyGanic 1.4EC) | 16–64 fl oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: Apply in sufficient water for thorough coverage. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | ||||
| C. | PYRETHRIN/PIPERONYL BUTOXIDE | |||
| (Pyrenone Crop Spray) | Label rates | 12 | 0 | |
| MODE-OF-ACTION GROUP NUMBER1: 3A/— | ||||
| COMMENTS: Variable efficacy. Not as disruptive of natural enemies as other options. | ||||
| ‡ | 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. |
| # | Acceptable for use on organically grown produce. |
| 1 | Rotate insecticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). |