How to Manage Pests

UC Pest Management Guidelines

Citrus

Ants

Scientific Names:
Argentine ant: Linepithema humile
Native gray ant: Formica aerata
Red imported fire ant: Solenopsis invicta
Southern fire ant: Solenopsis xyloni

(Reviewed 9/08, updated 6/13)

In this Guideline:


Description of the Pests   (household ant key)

The Argentine ant, is a small, uniformly deep brown ant. Worker ants travel in characteristic trails on trees, the ground, or irrigation lines and build their nests underground. Ant populations peak in mid-summer through early fall. 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. Native gray ants 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. Red imported fire ant is new to California and can make large, dome-shaped mounds. They feed on almost any plant or animal material.

Damage

Most pest ants feed on honeydew excreted by various soft scales, mealybugs, cottony cushion scales, whiteflies, and aphids. As part of this relationship, they also protect these insects from their natural enemies, thus interrupting biological control of the honeydew-producing pests. In the process of keeping most natural enemies away, they also protect other pests, such as California red scales, that profit from the lack of natural enemies. Argentine and native gray ants are the most common ant species that aggressively protect pest insects. In addition, Argentine ants and red imported fire ants can plug up irrigation sprinklers. Red imported fire ants directly damage plants by chewing twigs and tender bark of newly planted trees; they also sting people working in the orchard and may cause allergic reactions.

Management

Ants can be extremely disruptive to an IPM program. The Argentine, native gray, and fire ants can be prevented from climbing trees by skirt pruning and the use of sticky materials applied on top of a tree wrap to the bark as well as with insecticide treatments.

Biological Control

No effective natural enemies of the ants are known.

Cultural Control

Skirt prune trees, i.e., remove branches within 12 to 30 inches of the ground, and apply sticky material to the trunk to prevent access to the trees by ants. Use polybutenes; oil-based materials may cause phytotoxicity and should not be used. Sticky material should last from 2 to 10 months and will also prevent the access by Fuller rose beetles. If the sticky material contains tribasic copper sulfate, it will also control brown garden snails. The persistence of sticky material can be increased by applying it higher above the ground to reduce dust and dirt contamination and to decrease irrigation wash-off.

The application of sticky polybutene materials directly to the trunk of citrus trees can cause bark cracking, especially if multiple applications are applied to the same area of the trunk, the area is exposed to sunlight (topworked trees), or both. The sticky material can be applied on top of a tree wrap but this is both laborious and expensive. Young trees, which have a very thin cambium layer, are most susceptible to damage.

To prevent bark damage by southern fire ants, plant trees with the bud union about 6 to 8 inches (14–19 cm) above the soil surface. Irrigate as needed, but avoid applying water to the trunk and do not allow water to pond near the trunk. Periodically examine bark under trunk wraps of young trees. When trees are large enough, remove the trunk wraps, which provide protection for ants. If gum is observed, inspect and if necessary, treat for Phytophthora gummosis (see DISEASE section). Bordeaux whitewash helps prevent gumming, which attracts ants.

Cultivation reduces ant populations but may create so much dust that it disrupts biological control of other pests.

Organically Acceptable Methods

Cultural controls, including the use of sticky materials, and Gourmet Ant Bait are acceptable for use in organically managed citrus groves.

Monitoring and Treatment Decisions

Monitor the orchard in spring when honeydew-producing insects, such as aphids, appear. Check the abdomen of ants descending the tree trunks to see if they are swollen and translucent; this identifies them as honeydew-collecting species. Periodically inspect for ants and bark damage under the trunk wraps of several young trees.

Insecticides

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 or summer when ant populations are just beginning to increase and are becoming active on the ground surface. To determine which bait to use, identify your primary ant species; fire ants are predominantly protein feeders whereas most gray and black ants are sugar feeders.

Corncob Grit and Oil Baits

Solid baits utilize treated corncob grits mixed with soybean oil as the food attractant plus an insecticide. These are effective for the primarily protein-feeding fire ants. The toxicants tend to degrade in light, so apply baits 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 baits are broadcast over the acreage that needs to be treated. However, spot application of baits at the location of the ant nest is preferred over widely spreading the bait because it concentrates the food where the ants are.

Sugar-water-based Baits

Liquid baits use a toxicant mixed in sugar water, which disguises the toxicant as well as helps attract the ants. These baits are most useful for the liquid sugar-feeding Argentine and native gray ants. Evaporation of the bait can cause the concentration of the toxicant to increase to a level in the bait that becomes repellant to ants. All liquid baits must be used in an EPA-approved bait station.

Broad-spectrum Insecticide Sprays

The alternative to liquid sugar-bait stations or corncob grit baits is to use a broad-spectrum chlorpyrifos insecticide sprayed at the trunk and soil interface or inside the wraps of young trees. It is quicker acting than a bait, but not as long-lasting because the residue breaks down quickly. In addition, chlorpyrifos sprays kill only the worker ants that contact it on the soil surface, while baits are carried into the mound and fed to other ant stages.

Common name Amount to use R.E.I.‡ P.H.I.‡
(example trade name) (type of coverage) (hours) (days)

  Calculate impact of pesticide on air quality
 
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. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. STICKY POLYBUTENE MATERIALS# NA NA
  (Tanglefoot)
  RANGE OF ACTIVITY: Pests: narrow (trunk climbers); Natural enemies: few, if any
  PERSISTENCE: Pests: long; Natural enemies: long
  COMMENTS: For use on all varieties. Use polybutene-based products only. Do not apply sticky materials directly on the trunk; use a 6- to 18-inch wrap under the sticky material to protect the tree from sunburn. Exercise caution in applying multiple applications (more than 3 or 4); watch for symptoms of bark cracking. Apply the sticky band high enough to avoid sprinklers, dust, and direct sunlight. Reactivate periodically by rubbing with a stick to remove dust. Check to ensure that hanging branches, sticks, weeds, etc. are not allowing ants access to trees.
 
LIQUID BAITS
(Must be used in approved bait station such as KM Ant Pro or constructed from an approved design—PDF).
 
A. DISODIUM TETRABORATE#
  (Gourmet Liquid Ant Bait) 0 0
  RANGE OF ACTIVITY: Pests: narrow (sugar-feeding ants): Natural enemies: none
  PERSISTENCE: Pests: as long as the bait station is filled; Natural enemies: none
  MODE OF ACTION GROUP NUMBER1: unknown
  COMMENTS: Approved for organic growers only. Add additional solution when bait station is empty.
 
B. S-METHOPRENE
  (Tango)   4 0
  RANGE OF ACTIVITY: Pests: narrow (sugar-feeding ants); Natural enemies: none
  PERSISTENCE: Pests: as long as the bait station is filled; Natural enemies: none
  MODE OF ACTION GROUP NUMBER1: 7A
 
C. IMIDACLOPRID
  (Vitis Liquid Ant Bait)   0 0
  RANGE OF ACTIVITY: Pests: narrow (sugar-feeding ants); Natural enemies: none
  PERSISTENCE: Pests: as long as the bait station is filled; Natural enemies: none
  MODE OF ACTION GROUP NUMBER1: 4A
 
SOLID BAITS
 
A. ABAMECTIN
  (Clinch bait 0.011%) 1 lb/acre 12 0
  RANGE OF ACTIVITY: Pests: narrow (fire ants); Natural enemies: other ants
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  MODE OF ACTION GROUP NUMBER1: 6
  COMMENTS: A corncob grit and soy oil bait. For use on all citrus varieties. Effective only against fire ants because they are attracted to the soy oil mixed with corncob grits bait. Apply when fire ants are most active during the season (especially early summer and fall) and when they are most active during the day (early evening and early morning when soil temperature is above 60°F). Treatments are most effective if applied 2 days after an irrigation, when ant activity is at a maximum. Do not irrigate again until at least 24 hours after application. Do not apply if rainfall is anticipated with 4–6 hours after application. While Clinch can be broadcast using properly calibrated ground equipment to assure proper dosage and uniform distribution, spot applications at the location of the ant nest are preferred. Retreatment may be desirable after 3–4 months.
 
B. PYRIPROXYFEN
  (Esteem Ant Bait 0.5%) 1.5–2 lb/acre 12 1
  RANGE OF ACTIVITY: Pests: narrow (fire ants); Natural enemies: other ants
  PERSISTENCE: Pests: intermediate; Natural enemies: none
  MODE OF ACTION GROUP NUMBER1: 7C
  COMMENTS: A corncob grit and soy oil bait. For use on all citrus varieties. Effective only against fire ants because they are attracted to the soy oil mixed with corncob grits bait. Apply when fire ants are most active during the season (especially early summer and fall) and when they are most active during the day (early evening and early morning when soil temperature is above 60°F). Treatments are most effective if applied 2 days after an irrigation, when ant activity is at a maximum. Do not irrigate again until at least 24 hours after application. Do not apply if rainfall is anticipated with 4–6 hours after application. While this bait can be broadcast using properly calibrated ground equipment to assure proper dosage and uniform distribution, spot applications at the location of the ant nest are preferred. Retreatment may be desirable after 3–4 months.
 
INSECTICIDAL SPRAYS
 
A. CHLORPYRIFOS*
  (Lorsban Advanced) 1–3% solution (3–8 fl oz/gal water) 5 days See comments
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: short (low rates), intermediate (high rates); Natural enemies: short (low rates), intermediate (high rates)
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: For use on all varieties. Registered for ant control under a supplemental (24c) label when temperatures are warm and ants are most active. Apply by thoroughly spraying base of skirt-pruned tree trunks and ant nests on the ground. Repeat applications are needed. Preharvest interval is 21 days for up to 7 pt/acre or 35 days for over 7 pt/acre and 28 days for ant control.
  . . . or . . .
  (Lorsban 15G) 6.6 lb/acre 5 days 28
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: short (low rates); intermediate (high rates); Natural enemies: intermediate (low rates), long (high rates)
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Apply with ground equipment to control foraging ants and suppress mounds. Do not apply where weed growth or other obstructions would impede uniform coverage of the orchard floor.
 
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.
# Acceptable for use on organically grown produce.
* Permit required from county agricultural commissioner for purchase or use.
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). For additional information, see their Web site at http://www.irac-online.org/.
NA Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441

Insects, Mites, and Snails

  • E. E. Grafton-Cardwell, Entomology, UC Riverside and Kearney Agricultural Center, Parlier
  • J. G. Morse, Entomology, UC Riverside
  • N. V. O'Connell, UC Cooperative Extension, Tulare County
  • P. A. Phillips (emeritus), UC IPM Program, UC Cooperative Extension, Ventura County
  • C. E. Kallsen, UC Cooperative Extension, Kern County
  • D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgments for contributions to Insect, Mites, and Snails:
  • J. Barcinas, E.S.I., Corona, CA
  • R. Dunn, Badger Farming Co., Exeter, CA
  • J. Gorden, Pest Management Associates, Exeter, CA
  • H. Griffiths, E.S.I., Corona, CA
  • D. Machlitt, Consulting Entomology Services, Moorpark, CA
  • C. Musgrove, retired entomologist, Riverside, CA
  • K. Olsen, S & J Ranch, Pinedale, CA
  • T. Roberts, E.S.I., Corona, CA
  • T. Shea, UC Cooperative Extension, Riverside County
  • J. Stewart, Pest Management Associates, Exeter, CA
  • P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA

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