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Controlling Fire Ants
by Michael Waldvogel, NCSU Entomology & Plant Pathology
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A mound of this size (2' diameter/18'' high) contains about 100,000 workers, several hundred winged adults and one queen
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The red imported fire ant,
Solenopsis invicta
, continues to spread across North Carolina. This is due in part to favorable climate conditions & our increased residential and commercial development which often spreads ants (accidentally) in infested sod, nursery stock, soil, wheat straw, and other materials. Although fire ant stings are not fatal for most people, they are painful. Eradicating fire ants is difficult and not practical in many cases. However, you can manage infestations and cut the risk of getting stung. Fall is the best time to watch out for existing & newly developing mounds and to implement controls. Pesticides and baits work best when the temperature is between 70-85°F
Two aspects of red imported fire ant infestations are particularly annoying: the unsightly mounds and the painful stings received when mounds are disturbed. Mounds are typically constructed in open sunny areas and dome-shaped. If the mound is disturbed, ants swarm out and sting the intruder. Within 24 hours a pustule-like sore forms and itches intensively. Scratching can lead to a secondary infection and scarring. A small number of people are highly allergic to fire ant stings and require immediate medical attention.
Red Fire Ant Reproduction
If you break open an active fire ant mound, you typically find the "brood" - whitish rice grain-like larvae and pupae. These immature ants will eventually develop into workers or winged adults. During the spring and summer,
winged males and females
leave the mound and mate in the air. After mating, females will form their own nests - most don't survive; but when the queen does survive, she sheds her wings, burrows into the ground, and lays eggs to begin a new colony. In the late fall, many small colonies of fire ants will appear - that is why fall is the best time to treat.
Controlling Fire Ants with Integrated Pest Management
Red Fire ants forage for food by traveling in underground tunnels that radiate from the mound and then onto the surface (more mounds). You can reduce ant foraging around buildings by eliminating food sources:
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trash cans secure, spillage hosed down, no debris left on ground.
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check for ants in purchased sod, plants & mulch
Chemical Control
The most environmentally sound chemical approach is to treat individual mounds, NOT to broadcast over a large area. Mound treatment targets the fire ants & greatly reduces the impact on all other ground-dwelling insects.
Mound Treatments
Individual mounds may be treated with a liquid or dust insecticide formulation or with insecticidal bait. It is very important to read pesticide labels before you buy & before you apply. Many are NOT labeled for use in fruit & vegetable gardens or around livestock and poultry. Keep children and pets away from the treated area until it is dry. Always follow label directions when mixing & applying insecticides.
Drenches
are liquid insecticide treatments that must penetrate throughout the mound and contact most of the fire ants in the colony. They are mixed and poured right over the mound at the rate of 1 gallon for a 6" mound (2 gallons for a 12" mound, etc). It is the volume of insecticide drench that is most important. The ground must be wet to a distance of about 2' around the mound. Sometimes the drench does not kill all the ants and small mounds will emerge 10 to 15 feet out of the original mound. Several days after the application, search the area around the treated colony for new mounds and drench them as well.
Granular baits
can be used to treat individual mounds. These baits are a mixture of insecticide and food that is attractive to fire ants. Worker ants carry particles of the bait back to the mound and feed them to the "brood" (larvae or immature ants) and the queen. Although slower acting, bait treatments do not need water. Apply the bait according to label directions. Sprinkle the recommended amount around each mound (not on top of the mound itself). It is best to apply the bait in the early evening. Moisture renders bait ineffective so apply when the ground is dry.
Two-Step Method
A highly effective (but requiring more effort) is the "two-step method." Place the bait out around a mound. Wait about 5-7 days. Then, apply a mound drench which should kill the remaining workers more quickly.
Broadcast Applications
Broadcast treatments allow large areas to be treated quickly - but they are indiscriminate - they kill all the ground insects along with the fire ants. This makes broadcasting a poor environmental choice. Areas of high public use may be protected by spring and fall broadcast applications of ant bait or a well-timed granular insecticide. They are water activated so rain or irrigation must be applied shortly after the application.
Fire Ants Indoors
The key to reducing the threat of fire ant infestations indoors is prevention, which means removing exposed food sources that may attract these insects. In some cases, fire ants may nest indoors, e.g., inside walls or partially under concrete slab floors. In those instances, you will likely see soil and other debris pushed out around expansion joints near the edge of carpeting or around water or other utility pipes. In most situations, fire ants are simply entering the building from an outdoor nest. Treat immediately using an insecticide (not bait) labeled for indoor use. The best way to prevent indoor problems with fire ants is to control them outdoors when you find mounds.
Non-Chemical Control of Fire Ants
Reduce the amount of baits & pesticides used by implementing this strategy 1st.
Hot Water and Mechanical Disruption
Research shows that mound disruption & hot water (90°F+) poured directly into the mound kills large numbers of ants. As always, watch for satellite mounds that seem 5-7 days later and retreat. One potential downside to using hot water is that it can damage/kill vegetation in the general vicinity and can be hazardous to the person carrying hot/boiling water over uneven terrain. (Wearing boots & using a long-handled shovel, I dig a concave hole in the center of the mound then pour the boiling water in)
Grits - no
A long-standing folklore method of controlling fire ants that is not supported by the research. The ants do collect the grits, but there is no reduction in the number of ants in the colony.
Citation: Waldvogel, Michael. NCSU, 2019
2019 NC Agricultural Chemicals Manual
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