James Vogt and Art Appel

When fire ants colonize your yard, getting rid of these painful pests as quickly and effectively as possible is a top priority. AAES reseachers conducted a study recently to evaluate the effectiveness of several registered fire ant pesticides that are available to homeowners and can be used with no special training in pest control.

The red imported fire ant arrived in the U.S. in the 1930s, without any associated natural enemies, and has since spread to infest an area from coastal North Carolina south to Florida and west to central Texas. In the urban environment, fire ants can cause several problems. Mound-building activity in or beside central heating units and other electrical equipment can be destructive to the equipment itself, and is at the very least a nuisance. Mounds can also damage mowing equipment. Ants sometimes enter homes and carry soil indoors. Occasionally fire ants nest in potted plants. In yards, pet food can become infested with foraging worker ants. The primary concern facing homeowners is the danger of multiple stings and the possible accompanying reactions. Reactions can range from localized swelling and edema to severe cases in which respiratory distress may occur.

Homeowners must address several questions when deciding on a control strategy. Is immediate kill necessary, or is a slower-acting pesticide acceptable? Is it necessary to minimize risk of accidental exposure to pesticides, in cases where children or pets are present? What is the acceptable cost of control? These and other factors will direct the homeowner to the most appropriate control measure for their home.

Researchers tested six fire ant control products, each representative of common pesticide formulations and/or methods of application (see table for list of products). All products were applied to individual fire ant mounds according to label instructions. Mounds were marked with surveying flags in three locations (two in Lee County and one in Macon County), and a total of eight mounds were treated with each product. Mound activity was estimated by scratching the surface of each mound with a small stick and estimating the number of ants on the top of each mound 30 seconds after scratching. Mound activity was estimated one day before treatment applications and one, seven, 14, and 30 days after treatment. Results of the test are summarized in the figure.

Decline of red imported fire ant colonies, expressed as percent of original (pre-treatment) mound activity. Numbers larger than 100% indicate an increase in mound activity while numbers less than 100% indicate a decrease in mound activity.

It should be noted that the bait formulations tested—Ortho Fire Ant Bait, Combat Outdoor Ant Killing Granules, and Amdro Insecticide Bait—may require four to six weeks to work. These products have proven highly effective in other studies, but it takes more time for them to be distributed to all ants in a colony, particularly the queen. Also, these bait formulations can be applied as broadcast treatments to control fire ants over large areas. However, this test was designed to demonstrate products that provide prompt fire ant control in relatively small yards.

Two products—Hyponex Fire Ant Control and Spectracide Fire Ant Killer Granules—provided complete colony control within 24 hours of application. The active ingredients in both products are considered to be hard insecticides, which are effective against numerous insect species. Both products were watered into mounds according to label instructions, increasing the effort necessary for application.

Care must be taken during application to disturb the mound as little as possible, to avoid causing colony movement. Colony relocation is a natural process, but can be induced by disturbance to the mound. Colonies moved during the test regardless of treatment, with the exception of Hyponex and Spectracide. However, no conclusions about colony movement can be drawn from this study. The two treatments with the highest incidence of colony movement (seven total movements) were the untreated controls and Ortho Ant-Stop Fire Ant Killer. Ortho Ant-Stop, a non-bait product, provided rapid kill of some colonies, but other colonies moved and built new mounds nearby. Generally, when an old mound is found vacant and a new mound is seen within several feet, it is safe to assume that this is a sign of colony movement.

The bait formulations Amdro and Combat provided reasonable levels of control by day 14 (90% and 80% reduction in mound activity, respectively). However, Ortho Fire Ant Bait did not provide good control during the test. The active ingredient in this bait is a slow-acting insect growth regulator (IGR) that disrupts the reproductive cycle of the queen. Fire ant workers can live for several months, so an IGR bait is not suitable if very rapid control is required.

Baits do have advantages, primarily due to effectiveness against small, inconspicuous colonies not large enough for the homeowner to detect. Also, they generally require less effort for application and can be used over large areas. One control strategy often used is the broadcast application of a slow-acting bait, followed approximately one month later by individual mound treatments. This takes advantage of the baits effectiveness against less conspicuous colonies, while insuring elimination of larger colonies. It is very important when applying baits to be certain that weather conditions conform to suggestions on the label, since baits rely on foraging ants for their introduction into the colony.

Cost analysis for all treatments is presented in Table 1. Results of this study indicate that the cheapest, most effective means of controlling individual fire ant colonies is application of Hyponex Fire Ant Killer, at approximately 15 cents per mound. The most expensive product tested was Combat Outdoor Ant Killing Granules, at 67 cents per mound. In addition to this information, homeowners must consider the time and effort required for application and the required speed of control when deciding on a product to use. For example, Hyponex requires transportation of water to treated mounds, whereas Combat is fitted with an automatic dose-measuring device and requires no water.

Results of this study are not meant to be an endorsement of any of the products tested, but as an aid to the homeowner in addressing the above questions. In addition, the products tested do not represent all available treatment options. A more inclusive list of available products can be found in the Agriculture and Natural Resources Timely Information Sheet number T13, How to Treat for Fire Ants In and Around Homes, which is available at local county Extension offices. Additional information also can be found in the 1996 Pesticide Handbook.

Regardless of the means homeowners use to combat fire ants, it appears that fire ants are here to stay, and re-application will be necessary to control them. Colonies are capable of remarkable feats of movement from place to place (they can move several feet overnight), so in neighborhoods where residents wish to reduce fire ant populations it is desirable to communicate with neighbors and coordinate control efforts. Remember that once a colony is destroyed, neighboring colonies may move in to claim the area once occupied by the dead colony. It is evident, however, that with some effort and dedication, the homeowner can maintain a lawn that is relatively free of fire ants.

Vogt is a Graduate Research Assitant and Appel is an Associate Professor of Entomology.