Description of the Pest
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. Ants become active in spring as the soil temperature warms and peak in midsummer through early fall.
Native Gray Ants
Native gray ant (a common species in the San Joaquin Valley) is gray and considerably larger than the other two species. It moves about in a stop-and-start fashion. These ants construct nests with multiple entrance holes in areas with bare soil that are partially shaded. Native gray ant is relatively larger than southern fire ant or Argentine ant. 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. During hot daytime temperatures, the foraging activity of this species decreases considerably, while the native gray ant and Argentine ant remain active. Southern fire ant generally constructs nests in shaded areas with multiple, relatively small entrance holes. The tailings dispersed around the entrances appear fine-grain and hilly. Southern fire ant does not form colonies as large as those of the Argentine ant. When disturbed, southern fire ant will swarm from their nest and aggressively attack; they possess a painful bite and sting that can cause allergic reactions.
The Argentine ant is less common. They are small, uniformly deep brown ants. Workers travel in characteristic trails on trees, the ground, or irrigation lines. This species typically constructs nests at the tree dripline near a moisture source and nests have several entrance holes.
Most pest ants feed on honeydew excreted by aphids, mealybugs, whiteflies, and various soft scale. As part of this relationship, ants 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 honeydew-producing insects.
In addition, Argentine ants and southern fire ants can plug up irrigation sprinklers. Southern fire ants have a painful sting that may cause allergic reactions.
Ants can be very disruptive to an IPM program and play a key role in why aphids, whiteflies, mealybugs, and scales become a problem in pomegranate orchards. Fire ant numbers can be reduced with the use of solid, protein-based insecticide baits in bait stations. Bait can only be used when no fruit is present, limiting its use to early spring and late fall. There are currently no registered liquid sugar baits for native gray or Argentine ants, which will not be attracted to the solid bait. Cultural control methods may be an option.
No effective natural enemies of ants currently are known.
Cultural control options exist, but their use may have additional costs and other effects on management:
- Cultivation reduces ant numbers but may create so much dust that it disrupts biological control of other pests.
- Flood irrigation can reduce ant numbers 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 nectarines 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
Cultural controls are the only organically acceptable control methods for ants.
Monitoring and Treatment Decisions
Use visual searches to monitor the orchard in spring when honeydew-producing insects, such as aphids, appear. If fire ants are present, then apply bait in stations before fruit is present in the orchard.
There are currently no insecticides available for ants that feed primarily on sugary liquids, such as Argentine and native gray ants. For ants that feed primarily on proteins, such as fire ants, one insecticidal bait is available but has to be used in bait stations when no fruit is present. This bait has a slow-acting toxicant 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 numbers are just beginning to increase and are becoming active on the ground surface.
Corncob Grit and Oil Baits
The solid bait uses defatted corncob grit treated with soybean oil as the food attractant plus a registered insecticide. It is effective for the primarily lipid and 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, spot-treating can be employed by placing a bait station a few feet from a nest entrance. This is preferred since it concentrates bait nearer to the ants.
|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.|
|(Amdro Pro bait)||Label rates||12||See label|
|MODE-OF-ACTION GROUP NUMBER: 20A|
|COMMENTS: Use for fire ant control only. Must be applied in an EPA approved bait station. Do not apply when pomegranate fruit is present on trees.|
|‡||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.|