Fire ants can harm vegetable gardens


September 8, 2005


Victoria County Master Gardener


One of the primary responsibilities of master gardeners is to assist in providing answers to questions received via telephone calls at the County Extension office or through e-mail at This time of year always brings forth inquiries about fall vegetable gardening and one in particular relates to fire ants in vegetable gardens. Since fire ants are very hard to get rid of, let's see what we can do to manage them and still raise vegetables for consumption.


Soil preparation should be taking place now - and even some vegetables should already be planted by now. But just digging in the soil gets my blood boiling when fire ants find me. Fire ants are just about in every county in the state now - and while we can't eliminate them, there are some things we can do, even in our vegetable gardens, to minimize damage and pain caused by these pests. The information contained in this article will serve for both fall and spring vegetable gardens......


Vegetable gardens attract many different insects because gardens are well watered and contain oily seed pods or plant materials - and even other insects that fire ants feed on. These conditions are just what the fire ant is looking for. Once in the garden, the fire ant has been known to tunnel into potatoes underground, tomatoes above ground and feed on okra buds and developing pods. Insects found in the garden are usually considered prey by the fire ant. The aphid is one exception. Fire ants will protect aphids from their natural enemies for the sugary liquid waste they secrete called honeydew.


As we all know, some of us are especially vulnerable to the sting of the fire ant. The stings are painful and you can lose valuable gardening time trying to remove several hundred ants from your shoes, much less the pain and itching that lasts up to a week. How can you get so many bites so quickly? According to Nathan Riggs, extension agent-Integrated Pest Management (IPM) in San Antonio, we need to realize that along with the queen laying as many as 800 eggs a day, each mound can have about 200,000 workers protecting the mound and bringing in food. Once disturbed, they communicate quickly among themselves saying, "Somebody is about to get us, let's go get them first."


What can we do in our gardens ... places where we raise our food to feed our families?


Let's look at some options. According to Riggs, the only fire ant bait approved for use in the garden is Extinguish, which contains s-methoprene. It is an insect growth regulator and considered safe for all mammals. Other baits, containing products such as hydramethylnon, abamectin, fenoxycarb or pyriproxyfen, are not approved for vegetable garden use and should only be applied to the perimeter of the garden. Baits are attractive to worker ants inside and outside the garden; however, it will be six to eight weeks for effects to begin.


Pyrethroid insecticides, including esfenvalerate and cyfluthrin, are approved for use against fire ants in the garden if the wording for this use is found on the label. Not all companies making these products apply for approval, even though it is the same pesticides others get approved. These two pesticides will kill foraging ants on contact.


Carbamate insecticides containing carbaryl are effective against fire ants. You must read the label to determine if these products can be used against fire ants in the vegetable garden.


The latest in organic fire ant control is spinosid. This new organic product works quick and well according to the Harris County extension agent-IPM, Paul Nester. Labeled for gardens less than one acre in size, baits containing spinosid as well as spinosid sold as liquid and used as a mound drench perform well.


Organic methods for fire ant control in the garden, using pyrethrins plus diatomaceous earth as a mound drench, will also provide a quick kill with short-term residues. I have used this method myself with good results. Diatomaceous earth applied alone as a dust or water suspension to the mound may kill a few ants and will probably cause the colony to move but will probably not eliminate them. Other organic plant-derived products containing d-limonene (citrus oil extract), rotenone or pine oil extracts are approved against fire ants and may provide some relief.


The last method of managing fire ants to be addressed here is non-chemical. One or 2 gallons of very hot to boiling water poured on new fire ant mounds will kill the mound 60 percent of the time. You must be careful not to cook your plants or your feet.


By now, you are probably wondering why I did not provide many product names in this article. There are quite a few differently named products containing the same active ingredients I have discussed. Again, these products may or may not be approved for vegetable garden use against fire ants depending on the company's approval granted through the Environmental Protection Agency (EPA). When purchasing pesticides, shop by active ingredient and approved use to keep ourselves, our environment and others safe. Remember: READ THE LABEL, FOLLOW INSTRUCTIONS AND HEED WARNINGS.


If you are interested in fall vegetable garden plant lists and timeline guides by date for direct seeding and transplanting fall vegetable plants, refer to a previous article in this column archived at the Master Gardener Web site "Dig in Now: Get Ready for Fall Gardening."


And speaking of fall, don't forget to sign up for the Fall Gardening Symposium and plan to shop the Master Gardener Fall Plant Sale on Saturday, Sept. 24 at the 4-H Activity Center and Officer's Club at Victoria Regional Airport. Call the Extension Office at 361-575-4581 for more information.