Farewell to Fireants

— Written By and last updated by

If the recent warmer temperatures and breaks in the rain have you out inspecting your garden like I am, you may also have spotted the unfortunate tell-tale mounds of a particularly exasperating squatter. Fire ants. The red imported fire ant, Solenopsis invicta, continues to spread across North Carolina. Although fire ant stings are not fatal for most people, they are a painful nuisance. For over 60 years, this insect from Southern Brazil has made its unwelcomed home in NC. These days, portions or entire areas of 75 of NC’s 100 counties are considered generally infested with red imported fire ants.

Controlling fire ants in our homes and gardens is important and calls for an Integrated Pest Management (IPM) approach. First, shut down the lunch line. Fire ants prefer oily and greasy foods and search for it continuously. This foraging can bring them inside, so keep the trash cans tidy. Outdoor trash cans should be emptied frequently and keep the area around them clean. Keep shrubs pruned away from buildings so that ants can’t use them as a “bridge” to avoid treated areas. Because fire ants can be spread in new shrubs, sod, pine straw, and other landscape materials check these carefully before you buy and install them.

As the last piece of the IPM approach, there are two chemical control approaches to consider: an insecticide applied to individual mounds or broadcast over a wide infested area. Individual mound treatments use less insecticide and limit the amount of area treated as compared to broadcast treatments, but either way it’s important to destroy the queen as well as the workers because she is the only ant in the colony that is capable of laying eggs. Always follow the label directions when applying any fire ant insecticide.

Treat individual mounds with a liquid or dust insecticide formula or with an insecticidal bait. Liquid treatments may be done by rodding the chemical deep into the mound or by drenching the mound. The drench has to infiltrate the mound and come into contact with most of the fire ants at home in the colony where they will die soon after contact. Baits are a mix of an insecticide and desired food that the ants carry back to the mound and feed to the “brood” and queen. Baits can be slow acting but easier to apply than mound drenches. They are the best approach where many mounds must be treated, or when water for mixing mound drenches isn’t feasible, or when the risk of human or non-target animal contact is low and there is no pressing need to eradicate the infestation.

The active ingredients in ant baits break down in high temperature, high humidity, and intense sunlight and they can become ineffective in a few hours by these conditions. Consider the outdoor conditions when you are applying insecticide products, as well as where the products were stored before and after you purchased them as you need to use fresh bait with fresh food components that are still able to attract the ants. Test for ant “feeding interest” by placing a couple of fresh potato chips in areas of known or suspected ant mounds. If they take the chips, then apply the bait according to label directions. A study conducted at Florida State University determined that fire ants were most activity foraging was when the temperature of the soil at about an inch was between 70 and 95 degrees F. While fire ants will forage outside that range, these are their favorite temperatures. Sprinkle the recommended amount around each mound (not on top of the mound itself) in the early evening. By applying bait late in the day, it will be available to fire ants during their most favored time for foraging, throughout the night.

Broadcast treatments can be used over a large infested area containing many fire ant colonies. One disadvantage of broadcast treatments is that they can also disrupt other non-fire ant communities. Also, often granular insecticides (not granular baits) need to be watered in shortly after the application. When rain is not expected for several days or in areas where watering may be restricted or not feasible, a granular insecticide may not be the best choice.

Various products are produced for different areas of use. Contact your county Cooperative Extension center or consult the North Carolina Agricultural Chemicals Manual for information on fire ant insecticides appropriate for use by the general public and by public health and pest management professionals.