Homeowners Guide to Imported Fire Ants

Red imported fire ant, Eli Sarnat, PIAkey: Invasive Ants of the Pacific Islands, USDA APHIS PPQ, Bugwood.org
Black imported fire ant, Eli Sarnat, Antkey, USDA APHIS PPQ, Bugwood.org

Imported fire ants can cause serious medical, economic and ecologic problems. The red imported fire ant, Solenopsis invita, black imported fire ant, Solenopsis richteri and their hybrid are invasive insects. They were accidentally introduced from South America. They are called imported fire ants because they are not native to the United States.

Pustules on an infant’s hand formed by fire ant stings, photo by Kelly Palmer

Imported fire ants interfere with outdoor activities and harm wildlife throughout the southern United States and elsewhere. Ant mounds are unsightly and may reduce land values. Fire ant stings cause serious allergic reactions to a few and painful stings to most.

Although fire ants do prey on flea larvae, chinch bugs, cockroach eggs, ticks, and other pests, the problems they cause usually outweigh any benefits, especially in urban areas.

Fire ant management in home lawns

Fire ant baits

Pile of fire ant bait compared to size of quarter, photo by Kathy Flanders

Fire ant baits are one of the safest and most effective ways to manage fire ants.  Most bait formulations combine pesticide ingredients with soybean oil, which is absorbed onto processed corn grit. Soybean oil is an attractive food for ants that is important to the success of the bait. Ants select them as food to carry back to the colony and feed through the mound.  Because these baits are granular in texture, be careful not to confuse them with granular products that contain contact insecticides. Fire ant baits should have the word “BAIT”  listed somewhere on the label. Baits can be applied as spot treatments to individual mounds, in a bait station, or broadcast over large areas.

Broadcasting bait

Use fresh bait, preferably from a just-opened container or an opened one stored for no more than 2 years. Apply when worker ants are actively foraging. This can be determined by leaving a small pile (1 to 2 tablespoons) of bait in the area to be treated. Foraging activity slows when soil temperature is lower than 65 to 70 degrees F or higher than 90 degrees F.

In mid-summer, apply bait in late afternoon or early evening when the ground and grass are dry and no rain is expected. During the heat of the day, ants are less active or inactive due to hot soil. Applying bait in early evening also prevents it from being degraded by sunlight. In the winter, ants may not be foraging or be attracted to bait products and broadcasting bait is not recommended.

spreading fire ant bait
Example of hand-held seeder for broadcast fire ant bait applications at 1.5 pound per acre rate, photo by Bart Drees

Most conventional baits are applied at a rate of 1 to 1 1⁄2 pounds of product per acre. A few bait products are applied at higher rates. Periodic broadcast applications of fire ant baits will provide about 90 percent control when properly applied. A bait can be broadcast with hand-held spreader for the lower rates. Push-type seeders will not apply these baits at the recommended rate and will waste bait. There are products applied at higher rates that are designed for use with push-type lawn seeders, but the cost per unit area is higher for the convenience.

The advantage of broadcasting fire ant baits is that you can manage mounds that you cannot see.  A newly formed fire ant mound may remain under ground for 3 to 6 months.  Also, in the summer when temperatures are hot,  a disturbed mound may not rebuild and go unnoticed. Foraging ants from these mounds will still  recruit to bait and carry the toxin back to the mound. Since the ants recruit to the bait, the applications do not have to be uniform, can have skips and still be effective.

Hidden mound in lawn not rebuilt after mowing.

Individual mound treatments with baits

If you have a small yard with only have a few mounds, individual mound treatments with baits may be the method for you.  It requires more labor to find the mounds and treat each one individually. Most bait products for mound treatments are applied at the rate of 3 to 5 tablespoons per mound.  The bait is sprinkled around the mound so foraging ants can find it easily.

Baits are very safe for yards where children and pets play. They are selective for fire ants and leave little to no residue in the yard. Ants pick up the bait and carry it back to the mound where it is fed to the ants and young in the mound.

Fire ant carrying bait back to mound, USDA APHIS PPQ – Imported Fire Ant Station , USDA APHIS PPQ, Bugwood.org

Conventional contact insecticides

Most contact insecticides are sold as either granular, liquid or dust formulations. Their effectiveness depends on proper application. Contact insecticides must contact ants to work and should be applied during times of the year (and times of the day) when ants are close to the mound surface.

Individual mound treatment with contact insecticides

Although a few are ready-to-use, most fire ant mound drenches are formulated as liquid concentrates that must be diluted with the amount of water specified on the label. Pour the solution on top of and around an undisturbed mound. Most mound drenches require an hour to several days to eliminate the colony.

Individual fire ant mound treatment using chemical drench, photo by J., Summerlin.

To treat a single mound with a granular product, measure the amount recommended. Sprinkle it on top of and around the mound. Do not disturb the mound. If the label says to “water in” the insecticide, use a sprinkling can and water the mound gently to avoid disturbing the colony. Several days may pass before the entire colony is eliminated.

Treatment for fire ants with a granular product, photo by B. Drees

Some products are formulated as dusts for applying to individual fire ant mounds. Distribute the recommended amount of the powder evenly over the mound as recommended by the label.

Modified from Brad Vinson

Individual mound treatments work best when ants are near the top of the undisturbed mound. During the cooler months, ants are in the top of the mound where the sun warms the soil. In the summer, treatments are less effective. Ants reside in the cooler portion of the mound below ground.

Broadcast applications with conventional insecticides

For effective control, broadcast applications must be uniform across your lawn with no skips or overlap. Granular insecticides are applied with fertilizer spreaders. These materials must be thoroughly watered into soil after application as directed. Liquid formulations are applied with a pump-up, high-volume, hydraulic, hose-end or boom sprayer.

Granular spreaders must be calibrated for each granular product that you use. Different products have different granule sizes and flow differently out of the spreader. Care should be taken with rotary spreaders to determine the effective swath width. Swath edges need to be overlapped to ensure the product is applied evenly with no skips.

Liquid sprayers need to be calibrated to deliver the correct amount of product per 1000 sq. ft. Do this by spraying a known area of your yard with water. Record the time needed to treat this area. Then collect this amount in a graduated container to measure. This amount can be used to calculate ounces per 1000 sq. ft of product to apply.

Use of both baits and individual mound treatments – The Two-Step Method

One of the most effective ways to control fire ants is to use the broadcast applied ant baits as the primary control program. Then, a week or two later use individual mound treatments to spot treat mounds that survive the bait treatments or that ‘pop up’ between bait treatments. The individual mound treatments can be either liquid mound drenches, granular applications, dusts or individual mound bait applications.

Organic Insecticides

Several products said to be “organic” or of natural origin are currently marketed for fire ant control. These products may or may not be registered as pesticides by the EPA and the appropriate state regulatory agency. There are some OMRI listed® products for fire ant management. These products are used in the same manner as the conventional insecticides above. Follow label directions on all products.

Surface applications and barrriers in and around structures

Some products are used to treat ant trails and colonies located in structures and around structures. Unless the colony itself is treated, barrier treatments only reduce the number of foraging worker ants.

For more information check out these publications:

Managing Imported Fire Ants in Urban Areas

Calibrating Your Fertilizer Spreader

Calibrating Hand Sprayers

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