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.
UC IPM Pest Management Guidelines: Walnut
Insects and Mites
J. A. Grant, UC Cooperative Extension, San Joaquin County
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)