When you think of fire ants in the fall, "vulnerable" isn't the first word that pops into your mind. But it should be.

"If I could treat fire ants only once a year, I'd do it in the fall," said Beverly Sparks, a University of Georgia scientist.

Fire ants are easier to kill in the fall for four main reasons, said Sparks, an Extension Service and research entomologist in the UGA College of Agricultural and Environmental Sciences.

First, they're more active. That makes it easier to treat them with fire ant baits.

"You can use fire ant baits any time of the year. But they're most effective when the ants are actively foraging for food," Sparks said.

Fire ants are most active in spring and fall, when daytime temperatures are between 70 and 85 degrees, she said.

"Actively foraging ants will pick up a bait and carry it into the nest within minutes," she said. If the ants are inactive and don't find the bait quickly, it will become rancid. By the time the ants find it, it no longer appeals to them.

The second reason fire ants are vulnerable in the cooler weather of fall is that they're not too deep in the ground.

That makes them easier to kill with a mound-drench, granular, dust or aerosol contact insecticide. When you use those products, Sparks said, "it's critical to treat when the queen and brood are close to the surface."

Another advantage unique to the fall is that you are treating when many of the fire ant colonies in your yard are very young.

"Fire ants mate all during the year, but they're most actively mating in the spring," Sparks said. Mated queens fly off and establish new colonies. By fall, these colonies are well-established but still very small.

"Quite often you don't even know they're there," she said. "But if you don't treat them, they'll become the big mounds you see next year."

How do you treat them if you don't know where they are? Broadcast a fire ant bait.

That's the first step in the ongoing program Sparks recommends for fire ant control. Use a fresh bait, she said, and apply it by the label directions. Then treat individual problem mounds with an approved contact product. The final step is simply to repeat the first step once or twice a year.

The one thing that makes fall the single best time to treat fire ants, Sparks said, is that it's followed by winter.

Extreme cold is tough on fire ants, she said. That makes baits even more effective in the fall.

"Baits take a long time to work," she said. "They weaken colonies and make them less able to respond to the challenges of winter weather."

The young colonies are especially vulnerable, she said, because they don't have many workers. So they can't respond very quickly to the need to escape freezing temperatures.

The networked tunnels of a fire ant mound are constantly collapsing, she said. 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 structure makes the colony less able to survive winter weather.

"Winter is an ally in controlling fire ants," Sparks said. "Reducing their numbers in the fall can help push them over the edge in the winter."