How to Manage Pests

UC Pest Management Guidelines

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Walnut

Southern Fire Ant

Scientific Name: Solenopsis xyloni

(Reviewed 12/07, updated 4/09, corrected 4/09)

In this Guideline:

Description of the pest
Damage
Management

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. Ant hills often appear as small mounds or patches of loose soil. Fire ants vigorously swarm from the nest entrance when disturbed; nondamaging species do not. 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. The pyramid ant does not swarm.

DAMAGE

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.

MANAGEMENT

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**		R.E.I.+	P.H.I.+
(trade name)		(conc.)	(dilute)	(hours)	(days)

*When choosing a pesticide, consider information relating to impact on natural enemies and honey bees and environmental impact.*

NOTE: Baits must be used in an EPA-approved bait station (PDF).

A.	S-METHOPRENE	Label rates		4	0
	(Tango)

**	For concentrate application, use the amount given in 80–100 gal water/acre, or lower if the label allows; for dilute application, amount is per 100 gal water to be applied in 300–500 gal water/acre, according to label.
+	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 these two intervals is the minimum time that must elapse before harvest may occur.

PUBLICATION

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

Insects and Mites

C. Pickel, UC IPM Program/UC Cooperative Extension, Sutter/Yuba counties
J. A. Grant, UC Cooperative Extension, San Joaquin County
W. J. Bentley, UC IPM Program/Kearney Agricultural Center, Parlier
J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
Acknowledgment for contributions to Insects and Mites:
W. H. Olson, UC Cooperative Extension, Butte County
L. C. Hendricks, UC Cooperative Extension, Merced County
G. S. Sibbett, UC Cooperative Extension, Tulare County

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