How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

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 midsummer 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 and/or the area is exposed to sunlight (topworked trees). 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/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.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Insects, Mites, and Snails
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O‘Connell, UC Cooperative Extension, Tulare County
P. A. Phillips, 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 County, 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
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA
K. Godfrey, USDA Biological Control, Sacramento
D. Headrick, California Polytechnic State University, San Luis Obispo
B. Faber, UC Cooperative Extension, Ventura County
J. Kabashima, UC Cooperative Extension, South Coast Research and Extension Center

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