Fire Ant Control

fire ant mound

Caught Unaware

As a northern gardener who moved to the south, there were a few things that I had to get accustomed to. Climate and soil differences were obvious, and the adjustmments were relatively easy to make. One of the harder things to deal with has been fire ants.

Fire ants are plentiful and robust in our part of Georgia. You would think the hard clay soil might be a deterrent, but they seem to have an appreciation for it. Just last fall I counted 33 active mounds in the vacant 1 acre lot next to our home. That was only four years removed from a flood that seemed to wipe out the entire previous population. With a six year old son who likes to get out and explore, I knew it was time to do something about the menace.

Time for Action

To eradicate fire ants from the landscape, it helped to do a little research. Fire ants are omnivores, so cutting off their food source is not an option. Also, they were imported (accidentally) from South America, so there are no native predators…although a predator (parasitic phorid fly) has been imported for testing to help deal with the problem. That left a few options at my disposal: insecticide, physical elimination or biological control.

I have always tried to stay away from toxins as much as possible. It never fails…spray to kill one thing, and several innocent bystanders get whacked too. So, physical control may be a good option. Several sources, including my neighbor, recommended pouring boiling water over the mound. I’m sure this would work really well on a mound or two, but it would take lots of time and hauling of boiling water over an acre to cover all the mounds.  Another option which seemed viable at first was diatomaceous earth, which is a dust that tears up the exoskeletons of crawling insects. I’ve used it for other applications (fleas on the dog, sugar ants at the baseboards, slugs on vegetable plants, etc.). The problem is, it’s impossible to get the dust into the mound where it would actually do some good; so that option was out too.

The Trojan Horse

Which lead me to biological control: spinosad. I have sold spinosad sprays for foliar treatment of various bug infestations on plants back when I worked as a nursery manager, but it had never occurred to me to use it on fire ants until I read the label on a “natural” brand of fire ant bait. The key with bait is that it takes advantage of the ant’s scavenging and societal habits. The workers eat some, and bring it home to the family who eat the rest. It’s great because there only needs to be a small amount of the active ingredient to be extremely effective.  A spinosad based bait is a bonus because it uses a derivative from a naturally occurring bacteria as it’s active ingredient. I bought it and used it as instructed for a mound treatment application, and waited.

After about a week I stirred up a couple of the mounds to see if there was any reaction. One small mound was dead.  A larger mound seemed weak. Instead of boiling out of the pile, as is the normal reaction to poking the mound, the ants sort of wandered out. By about six weeks after treatment, virtually all of the mounds were defunct and some had even collapsed. I treated the mounds in August, and by the end of October there was no longer a fire ant problem. (I am now revisiting the potential of spinosad for treating Mexican bean beetles in my vegetable garden…we’ll see if it gets that bad.)

But not to worry.  As I stated previously, our fire ants are robust and plentiful.  A year after successful treatment, fire ants have taken up residence in the lot again (although in about half the strength of the previous infestation). While I do not believe that the population building a tolerance to spinosad is an issue, I will try another approach this year in the name of discovery. I have since been told that orange oil (which contains d-limonene) mixed with water and dish soap has an immediate and deadly reaction when used to drench the mound. I’ll let you know how it goes…

Happy gardening!

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