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How to Manage Pests

UC Pest Management Guidelines


Fruit fly larvae.

Strawberry

Vinegar Fly

Scientific Names: Drosophila melanogaster and other species

(Reviewed 6/08, updated 5/10)

In this Guideline:


DESCRIPTION OF THE PESTS

Vinegar flies, also known as fruit or pomace flies, are small, yellowish flies that are commonly attracted to fermenting fruit of all kinds. Populations may build up as the freezer harvest season progresses and temperatures become warmer, especially in southern California. The 0.25 inch (6 mm) long 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 population buildup of vinegar flies, 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 sticky traps to help detect infestations as early as possible.

Cultural Control
Limit breeding sites for fruit flies. Make certain that ripe fruit are completely removed from the plants. When possible, shorten harvest intervals as temperatures increase. Practice good sanitation in and around the field. Identify and try to clean up external sources of flies such as cull piles of strawberries or other rotting fruit and nearby citrus groves where old fruit may be on the ground.

Organically Acceptable Methods
Cultural controls, especially field sanitation, and pyrethrin sprays are acceptable for use on organically certified strawberries.

Monitoring and Treatment Decisions
Although no monitoring or treatment guidelines exist for vinegar flies in strawberries, yellow sticky cards can be used to monitor adult fly populations. Adults and their offspring may also be monitored using fermented fruit traps consisting of a container filled with overripe fruit covered with an inverted funnel. High populations 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 treat 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 treatments 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 treat for adults is between 8 and 11 A.M.and between 5 and 7 P.M.

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

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. MALATHION
  5EC 1.5–3 pt 12 3
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Provides effective control.
 
B. PYRETHRIN#
  (PyGanic) 1.4EC 16–64 oz 12 0
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Apply in sufficient water for thorough coverage.
 
C. PYRETHRIN/PIPERONYL BUTOXIDE
  (Pyrenone) Label rates 12 0
  MODE OF ACTION GROUP NUMBER1: 3/—
  COMMENTS: Variable efficacy. Not as disruptive of natural enemies as other options.
 
D. DIAZINON* 50WP 2 lb 3 days 5
  MODE OF ACTION GROUP NUMBER1: 1B
 
+ 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: Strawberry
UC ANR Publication 3468
Insects and Mites
F. G. Zalom, Entomology, UC Davis
M. P. Bolda, UC Cooperative Extension Santa Cruz County
P. A. Phillips, UC IPM Program/UC Cooperative Extension Ventura County
Acknowledgment for contributions to the Insects and Mites:
N. C. Toscano, Entomology, UC Riverside

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