Fire-ant treatments are most effective in the fall

Fire ants were very active this summer because heavy rains drove them to build higher mounds. In the fall, many colonies are filled with immature ants that are more susceptible to baits designed to eliminate them.

Fire ants have been bad this summer because of all the rain. Wet conditions drive them out of the ground as they build mounds higher to get away from the moisture. The ground has dried out lately, but the ants’ actively will pick up again as the weather cools. Fire ants are most active in the fall and spring when daytime temperatures are between 70 and 85 degrees.


Mid-September through mid-October is the best time to treat for and kill fire ants. There are many control products available, but perhaps the best is a bait.

Fire ant baits consist of pesticides on processed corn grits coated with soybean oil. Several are on the market, but probably the only one you will find in most retail centers is Amdro. Others you might see are Award, Ascend, Extinguish, Spectracide and Pennington Fire Ant Bait..

Treat your yard late in the day when it is dry and rain is not forecast for at least 24 hours. After the bait is on the ground, foraging ants will pick up and carry it into the nest within minutes. If the ants don’t find bait quickly, it will become rancid and no longer appeal to them.

Fire ants are vulnerable to insecticides in cooler weather because their nests are not very deep. That makes them easier to kill with a mound drench, granular, dust or aerosol contact insecticide. When you use these products it’s critical to treat when the queen and brood (eggs, larvae and pupae) are close to the surface.

Another advantage in fall is that you are treating when many of the fire ant colonies in your yard are young. Fire ants mate almost year-round except for two or three winter months, but they’re most actively mating in the spring. The mated queens fly off and establish colonies. By the time fall rolls around, these colonies are well established but still small. Quite often, you don’t even know they’re there unless we get a lot of rain to bring the mound up and out of the ground.

You might say it’s hard to treat a mound when you don’t know it’s there. This is why baits can be so effective. Use fresh bait and apply it by label directions. It doesn’t take much, usually 1 to 11/2 pounds per acre. Baits should eliminate 80 percent to 95 percent of fire ant mounds.

Another thing that makes fall the best time to treat fire ants with bait is that it is followed by winter. Cold weather is tough on fire ants. Baits take a few weeks to work, but they weaken colonies and make them less able to respond to the challenges of winter. Young colonies are especially vulnerable because they don’t have many worker ants.

The network of tunnels of a fire ant mound is constantly collapsing. Moving deeper into the ground requires a lot of work. Anything you can do to reduce the number of ants available to gather food and maintain the mound makes the colony less able to survive winter.

Baits are by far the most economical option if you have a large yard of perhaps an acre or more.

For smaller areas, or where you need zero ants, use a broadcast application of a contact insecticide. Examples are those with pyrethroids, which are active ingredients ending in “thrin” such as bifenthrin, permethrin, cypermethrin, or cyfluthrin.