How to Manage Pests

UC Pest Management Guidelines

Pomegranate

Ants

Scientific names:
Native gray ant: Formica aerata
Southern fire ant: Solenopsis xyloni
Argentine ant: Linepithema humile

(Reviewed 10/13, updated 10/13)

In this Guideline:


Description of the pests

Ants are commonly found in pomegranate orchards and reducing ant numbers improves the biological control of honeydew-producing insects such as aphids. Unfortunately, there are few chemical choices for ant control currently available, but cultural control methods may be an option. Ant populations become active in spring as the soil temperature warms and peak in midsummer through early fall.

Native gray ants

Native gray ants (the most common species in the San Joaquin Valley) are gray and considerably larger than the other two species. They nest in topsoil or under rocks and debris and move in irregular patterns. In contrast to Argentine and fire ants, the native gray ant is solitary and its importance in disrupting biological control is often underestimated.

Southern fire ant

The southern fire ant is light reddish brown with a black abdomen. These ants build nests of loose mounds or craters near bases of trees, do not aggregate in colonies as large as those of the Argentine ant, and will sting and bite.

Argentine ant

The Argentine ant is less common. They are small, uniformly deep brown ants. Worker ants travel in characteristic trails on trees, the ground, or irrigation lines and build their nests underground.

Damage

Most pest ants feed on honeydew excreted by aphids, mealybugs, whiteflies, and various soft scales. As part of this relationship, ants also protect these insects from their natural enemies, thus interrupting Biological control of the honeydew-producing pests. Native gray ant, Southern fire ant, and Argentine ant each actively tend these insects.

In addition, Argentine ants and southern fire ants can plug up irrigation sprinklers. Southern fire ants can also sting people working in the orchard, which may cause allergic reactions.

Management

Ants can be very disruptive to an IPM program and are an important reason why aphids, whiteflies, mealybugs, and scales become a problem in pomegranate orchards. Fire ant numbers can be reduced with the use of insecticide bait in bait stations. Bait can only be used when no fruit is present, limiting their use to early spring and late fall. There are currently no registered liquid sugar baits for the other ants, which will not be attracted to the solid bait. Cultural control methods may be an option.

Biological Control

No effective natural enemies of ants currently are known.

Cultural Control

Cultural control options exist, but their use may have additional costs and other effects on management. Cultivation reduces ant populations but may create so much dust that it disrupts biological control of other pests. Flood irrigation is another method that reduces ant populations in orchard systems. However, a possible loss in irrigation and weed management efficiency should be considered if the flood irrigation method is used.

Other cropping systems have shown the value of common vetch (Vicia sativa) grown as a spring cover to attract native gray ants from the honeydew-producing insects in the trees to the many nectaries in the cover crop. In grapes, an 80:20 mix of vetch:Merced rye planted in the fall or winter did well in attracting ants in the spring and early summer. Whether cover crops are attractive to other ants or if it provides this level of attractiveness in pomegranate has not been researched.

Organically Acceptable Methods

There are currently no organically acceptable control methods for ants.

Monitoring and Treatment Decisions

Monitor the orchard in spring when honeydew-producing insects, such as aphids, appear using visual searches. If fire ants are present then apply bait before fruit is present in the orchard.

Insecticides

There are no currently registered spray insecticides for ant control. Baits are the preferred chemical method for ant control whenever feasible. Effective bait insecticides have slow-acting toxicants that worker ants collect and feed to other ants, including nest-building immatures and queens. For the most effective and economical ant control, treat in early spring when ant populations are just beginning to increase and are becoming active on the ground surface. Argentine ants are liquid feeders and so the solid baits are not effective against this species.

Corncob grit and oil baits

The solid bait uses treated corncob grits mixed with soybean oil as the food attractant plus a registered insecticide. It is effective for the primarily protein-feeding fire ants. Place bait stations out early in the morning or late in the day when ants are active and will take the bait into the nest. Generally, corncob grit type bait stations are placed throughout the acreage that needs to be treated. However, placing bait stations at the location of the ant nest is preferred because it concentrates the food where the ants are.

Common name Amount per acre R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
 
When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. HYDRAMETHYLNON
  (Amdro Pro bait) Label rates 12 See label
  MODE-OF-ACTION GROUP NUMBER1: 20A
  COMMENTS: Use for fire ant control only. Must be applied in bait stations. Do not apply when pomegranate fruit is present on trees.
 
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 R.E.I. exceeds the P.H.I.. The longer of two intervals is the minimum time that must elapse before harvest.
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: Pomegranate
UC ANR Publication 3474

Insects and mites

  • E. E. Grafton-Cardwell, Entomology, UC Riverside and Kearney Agricultural Center, Parlier
  • D. Carroll, Bio Ag Services, Inc., Fresno
  • W. J. Bentley, UC IPM Program (emeritus), Kearney Agricultural Center, Parlier
  • D. R. Haviland, UC Cooperative Extension, Kern County
  • V. Walton, Horticulture, Oregon State University (filbertworm)

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