How to Manage Pests

UC Pest Management Guidelines


Southern Fire Ant

Scientific Name: Solenopsis xyloni

(Reviewed 7/17, updated 7/17)

In this Guideline:

Description of the Pest   (household ant key)

The southern fire ant is 0.07 to 0.25 inch (1.7–6 mm) long, has an amber head and thorax with a black abdomen. It has a painful sting that causes visible swelling. Anthills often appear as small diffuse mounds or patches of loose soil.

Nests in orchards with low-volume irrigation tend to be located around the edges of the wetted areas. In flood-irrigated orchards with heavy soils, nests tend to be concentrated on the berms. Where lighter soils are present, nests are located both on the berms and in the middles. Frequently, southern fire ants nests are associated with clumps of weeds, such as nutsedge or spotted spurge.

Activity of these ant pests peaks in the morning and again just before sunset. Do not confuse southern fire ant with the pyramid ant, which is a beneficial species that is similar in size but active during mid-day and found in sandy, weed-free areas. Fire ants vigorously swarm from the nest entrance when disturbed; nondamaging species, such as the pyramid ant, do not.


The southern fire ant has a wider distribution and generally causes more damage than the pavement ant. Ants are more prevalent in drip- or sprinkler-irrigated orchards than flood irrigated orchards. Ants feed on other hosts and are principally a problem after walnuts are on the ground; nut damage increases in relation to the length of time they are on the ground. They enter nuts through the soft tissue at the stem end or through a codling moth injury.


If prolonged nut drop occurs and ants have been a problem in the past, a bait application may be needed in August.

Common name Amount to use** REI‡ PHI‡
(Example trade name)   (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
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.
  (Esteem Ant Bait) Label rates 12 1
  (Clinch Ant Bait) Label rates 12 0
  (Extinguish Professional Fire Ant Bait) Label rates 4 0
  (Altrevin Fire Ant Bait) Label rates 12 5
** For concentrate application, use the amount given in 80 to 100 gal water/acre, or lower if the label allows; for dilute application, amount is per 100 gal water to be applied in 300 to 500 gal water/acre, according to label.
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 these two intervals is the minimum time that must elapse before harvest may occur.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

Insects and Mites

J. A. Grant, UC Cooperative Extension, San Joaquin County
J. K. Hasey, UC Cooperative Extension, Sutter, Yuba, and Colusa counties
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
E. J. Symmes, UC IPM Program, Butte County
S. J. Seybold, Entomology, UC Davis (walnut twig beetle)
R. M. Bostock, Plant Pathology, UC Davis (walnut twig beetle)

Acknowledgment for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Research and Extension Center, Parlier (Emeritus)
L. C. Hendricks, UC Cooperative Extension, Merced County (Emeritus)
W. H. Olson, UC Cooperative Extension, Butte County (Emeritus)
C. Pickel, UC IPM Program, Sutter and Yuba counties (Emeritus)
G. S. Sibbett, UC Cooperative Extension, Tulare County (Emeritus)
D. Light, USDA, Albany, CA (Emeritus)(Codling Moth)

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