Fire ants. Just hearing the words will make most Southern gardeners anxiously check their shoes and the ground where they are standing. These non-native stinging ants are established in portions of 12 southeastern states, and six of these states – Louisiana, Mississippi, Alabama, Georgia, Florida and South Carolina – have fire ants from border to border.
Fire ants prefer treeless grassy areas such as pastures, roadsides, parks and lawns, and densities can reach 50 to 200 mounds per acre in areas where they are not controlled. Fire ant mounds are unsightly, but it is their stings that make them so notorious. Unlike honeybees, fire ants do not have barbs on their stingers, and this means they can sting more than once. A single fire ant sting is painful, but unsuspecting gardeners sometimes sustain dozens or even hundreds of stings as a result of unknowingly stepping in a fire ant mound. The raised white pustules that result usually persist for about a week.
Fire ants reproduce by swarming. Winged male and female fire ants emerge from mounds, fly hundreds of feet into the air, find one another and mate. During this time wind currents can carry these airborne ants several miles. Mated females fall to the ground, shed their wings, and attempt to start a new colony. It takes several months for such a colony to grow large enough to be visible above the grass. Swarming can occur any time of the year, but is most common during warmer months.
The granule of fire ant bait this worker is carrying contains a slow-acting ingredient that does not kill immediately, giving her time to carry the bait back to the mound and share it with other ants.
These brief notes on fire ant biology help answer two of the most common questions about fire ant control. Why do they keep coming back? Because even if you kill every fire ant in the yard, newly mated queens are constantly dropping out of the sky to start new colonies. Why is it that when I kill one mound two or three more pop up to take its place? Because for every large mound you can see, there may be a dozen or more young colonies that are not yet large enough to be seen. Eliminate the foraging competition from the large mound and these small colonies grow faster. This is why attempting to control fire ants by only treating mounds you can see usually produces less than satisfactory results. It’s a lot like playing whack-a-mole.
So what’s the key to successful fire ant control? One of the most effective ways to control fire ants is to hit them with a one-two punch. Use granular fire ant baits as the foundation of your fire ant control program and keep a can of one of the dry fire ant mound treatment products on hand to spot-treat mounds that survive the bait treatments. When used properly, baits will give around 80 to 90 percent control, leaving a lot fewer mounds to spot treat than if you rely on mound treatments alone.
A small, hand-held spreader is the best tool for spreading granular fire ant baits. Application rates are low; you will probably need to use one of the lowest settings.
Granular fire ant baits contain slow-acting insecticides or insect growth regulators that disrupt development of the immature fire ants, active ingredients such as hydramethylnon, methoprene, pyriproxyfen, spinosad or indoxacarb. The key to using baits successfully is to spread them over the entire yard, rather than sprinkling them on top of individual mounds. Application rates are low, only around 1-1.5 pounds per acre, which is only a fraction of an ounce per 1,000 square feet. Foraging worker ants will collect the granules, carry them back to the mound, and feed them to the immature ants. Ultimately, the bait will be spread to all the ants in the colony. It can take two to six weeks to begin seeing control from a fire ant bait treatment, but the end results are devastating to fire ants. The other key to using baits successfully is to apply them preventively about three times per year: spring, summer and fall. Don’t wait until you start seeing more fire ant mounds in your yard to apply that next bait treatment. Remember big fire ant mounds start with a single queen and a few workers, and these young colonies are not readily visible. One of the reasons baits work so well is that they kill the small colonies that are just getting started, as well as the larger colonies.
Dry mound treatments contain active ingredients like acephate, beta-cyfluthrin or deltamethrin. Products containing acephate smell really bad, but they are more effective and work faster than the less odorous products. These treatments are applied directly to the mound; just sprinkle the specified amount evenly over the top of the mound and walk away. Depending on which product you use, it takes a couple of days to a week or so for the mound to die out. For mounds that need to be controlled immediately use a liquid drench containing an active ingredient like carbaryl or permethrin. Dilute in water as indicated on the label and pour the drench over the mound. Liquid drenches kill quickly, but are more messy and time-consuming than dry mound treatments. The key to success with drenches is to use enough liquid to thoroughly soak the mound, about 1-2 gallons.
Your local county extension office can provide more information on fire ants and how to control them, including more detailed information on how to use liquid mound drenches and other effective control methods not discussed here. Fire ants are persistent pests and gardeners must be equally persistent to achieve and maintain acceptable control. But if you learn to use fire ant baits properly and supplement them with individual mound treatments, then yes, you can control fire ants.
Knock Out Fire Ants with a One-Two Punch
1. Use a hand-held spreader to spread granular fire ant bait over your yard three times per year. Use the holidays: Easter, Independence Day, and Labor Day to remind you it is time to apply fire ant bait.
2. Keep a can of one of the dry fire ant mound treatments handy to spot treat mounds that escape the bait treatments.
A version of this article appeared in an April 2015 print edition of State-by-State Gardening.