Managing Imported Fire Ants in Agriculture

The red imported fire ant, Solenopsis invicta Buren, is an introduced species that arrived in Mobile, Alabama from South America during the 1930’s. This species has had an enormous impact in the southeastern United States, and continues to spread into areas of North America with mild climates and adequate moisture and food. Approximately 367 million acres in the southeastern United States, California, New Mexico and Puerto Rico are currently infested. A second exotic species, the black imported fire ant, Solenopsis richteri Forel, and hybrids between S. invicta and S. richteri occur in northern Alabama, Georgia, Mississippi and Tennessee, but not farther west.

Imported fire ants, hereafter referred to as fire ants, impact agriculture in a number of ways. They form hardened mounds in clay-type soil tall enough to damage field equipment and slow down operations. Ants defending mounds can sting and cause medical problems for field workers. The ants have an affinity for electrical units, utility housings and structures, where they can cause equipment failures. Worker ants may feed on some seeds and seedlings (sorghum, corn, small grains, forages, etc.) causing stand failure.

Fire ants prey on a number of pest insects and arthropods, including boll weevils, many species of caterpillars, flea larvae, ticks, and chiggers as well as beneficial insects like green lacewing larvae. They will also “tend” some species of sucking insects (aphids, mealybugs) which provide them with a sugary solution (honeydew) upon contact. Fire ants have displaced many native ant species and eliminated food used by some wildlife. Fire ants can affect newborn livestock and wildlife, especially those animals on the ground or those nesting on the ground or in low trees. Multiple fire ant stings can cause medical problems or even death to some animals. Although the research is not conclusive, populations of some wildlife species may be dramatically reduced.

Fire Ant Biology

Like other ants, the fire ant is a social insect.  Colonies reside in the soil and can build mounds that may exceed 18 inches in height. Fire ant mounds commonly occur in open, sunny areas. Periodically, winged reproductive male and female ants leave colonies on mating flights. Mated females (queens) can fly or be carried by winds for miles, land and start new colonies. Development from egg to adult occurs in about 30 days, progressing though four larval stages and a pupal stage. Worker ants (sterile female ants capable of stinging) can number in the hundreds of thousands in a mature colony.

Fire ant workers tending a queen. Photo by Charles Barr.

Two forms of fire ants occur: single queen (monogyne) and multiple queen (polygyne) colonies. Areas infested by the single queen form may have 40 to 80 colonies per acre. Multiple queen colony infested land can harbor 200 to 800 or more ant mounds per acre. Worker ants from multiple queen colonies are not territorial and move freely from mound to mound. The opposite is true of workers from single queen colonies. Fire ant mounds can rapidly increase in number after agricultural lands are disturbed by mechanical operations or pesticide use. Due to the fire ants’ ability to form a mass of floating bodies, flooding can temporarily move fire ants out of flood prone areas and into areas that were not previously infested.

The fire ant disperses naturally through mating flights, mass movement of colonies or by floating to new locations in flood water. Fire ants can travel long distances when newly-mated queens land in cars, trucks or trains.  Shipments of hay, nursery stock or soil from an infested area may relocate entire colonies or nests (see Quarantine Regulations).  More information on fire ant biology can be found here

USDA Quarantine Program

Because fire ants are easily transported in nursery stock and soil, the United States Department of Agriculture (USDA) developed a quarantine program for this pest in the 1950s. This quarantine is designed to minimize the spread of the fire ant by requiring proper treatment and inspection of all nursery stock, turfgrass, hay and other articles shipped out of quarantined counties. Contact your state’s Department of Agriculture for specific information regarding compliance with these quarantine regulations.

Integrated Pest Management (IPM)

This bulletin provides site-specific, goal-oriented management programs for agricultural situations where fire ant problems occur. You should select programs that use, where applicable, a combination of non-chemical and chemical methods that are effective, economical and least harmful to the environment. The goal of fire ant management is to prevent or reduce problems caused by unacceptably high numbers of fire ants.  The worksheet at the end of this article may help in deciding the cost of fire ants in a particular operation.

Every effort should be made to direct control efforts only at the fire ant. Preservation and encouragement of competitor native ant species is thought to be the best long-term solution. Native species can reduce fire ant population densities by competing with them for food and resources, as well as control other pests.

Integrated Pest Management (IPM) is a concept used in many areas of agriculture to help producers determine if the cost of pest control can be offset by production gains before treatments are applied. The first step in any IPM program is to find out if, how often, and where losses occur and how much those losses actually cost. It is up to the individual to decide what “counts” as a fire ant-related loss and to put a value on that loss. If there is some question, it is often a good idea to make two assessments: one for definite losses and one for losses that might be attributable to fire ants. This method provides a range within which treatment expenditures can be adjusted.

In theory, management efforts should be implemented only where the monetary loss caused by a certain level of a fire ant population density equals or exceeds the cost for controlling them. This is the Economic Injury Level (EIL). The Economic Threshold (ET) is the level set below the EIL at which action is justified to prevent economic losses from occurring. Losses caused by the fire ant, however, are erratic and unpredictable. Loss estimates are best made from historical accounts on a given property.

Livestock Production Systems, Pasturelands, Rangeland, Feedlots and Livestock Barns

Fire ant problems in livestock production systems are widespread and costly, but vary tremendously from ranch to ranch, even within the same locality. As a result, no “one size fits all” management plan can, or should, be used.  More information on this topic is found in Managing Imported Fire Ants in Livestock Production Systems,  Losses must be determined on an individual operation basis (see the worksheets at the end of this article or the Livestock Production article) and treatment plans tailored to minimize those losses at an acceptable cost.

In animal feeding stations, barns and feedlots, fire ants can cause problems similar to those found in poultry houses. Therefore, the programs for poultry houses (see below) can be adapted to treat fire ants in livestock barns and holding pens, provided products used are labeled for treating animal premises.  Around barns and other structures use the Two-Step Method, provided the treated areas are inaccessible to animals and registered products are used. Conventionally-formulated bait products, such as Abamectin (Clinch®), hydramethylnon (Amdro® Pro), or pyriproxifen (Esteem®) can be broadcast-applied outside livestock pens according to directions. S-methoprene (Extinguish®) bait can be used in pens with no withdrawal or grazing restrictions.

Poultry Including Free Range Chickens

Fire ants can cause problems on poultry farms by attacking chickens and foraging on broken eggs.  Fire ant stings cause blemishes that can reduce the quality of poultry.

Treatment options:

Program 1:  For poultry houses and egg farms (use a combination of the following suggestions)

1. Remove food sources (trash, piled feed, broken eggs and dead chickens) and potential nesting sites (pieces of lumber, old equipment and manure piles).
2. Remove weeds and grass from around poultry houses with mowers or herbicides.
3. Indoors, treat surfaces with a registered product if ants are nesting inside poultry houses.  Note: Although some products like  permethrin (Y-Tex® GardStar®) are registered specifically for control of fire ants in poultry houses, other products, like cyfluthrin (Countdown™), dichlorvos (Vapona® Concentrate Insecticide), and lambda-cyhalothrin (Grenade™ ER Premise Insecticide), are more generally registered for “crawling pests” — including ants. Read the poultry section of labels for additional precautions. Do not allow insecticides to come into contact with feed or water supplies.
4. If fire ants are foraging inside the poultry house from ant mounds located outdoors, spray a barrier around the outside of the building with products registered for that usage site (e.g., lambda-cyhalothrin).
5. On grounds surrounding the buildings, use the Two–Step Method.  Briefly, the Two-Step Method relies on the periodic (once or twice per year) broadcast application of an effective fire ant bait product.  These treatments can reduce mound numbers by 90 percent, but reduction requires several weeks to months to achieve, depending upon the product chosen. The second step uses individual mound treatments to treat only “nuisance colonies”. However, with patience, few mounds will need to be treated once the broadcast bait treatment has taken effect. Always read and follow closely the instructions provided on the product’s label. Conventionally-formulated bait products, such as Abamectin (Clinch™), hydramethylnon (Amdro®), pyriproxifen (Distance®) or s-methoprene (Extinguish™) can be broadcast-applied outside the poultry house. Do not allow chickens access to fire ant bait or bait-treated areas.

Program 1 for egg farms can be adapted to broiler houses, provided the products used are registered for this site. Because the broilers roam freely in the houses, care must be taken to avoid contact of chickens with insecticides by confining treatments to the outside of the broiler house (see Step 5 above).

Program 3: Free Range Poultry

Deciding how to manage fire ants where there are free ranging birds is a bit complicated.  Free range means different things to different people.  The labels for various fire ant control products may specifically mention penned animals or penned birds, but not address birds that might be ranging across lawn or pasture areas.  In addition, state governments differ in how insecticide labels are interpreted.

Fire ant experts recommend using a bait-based approach for safe and effective control of fire ants in areas with free ranging birds.  Choose a bait that is labeled for the site where the birds are ranging, for example, animal pen, lawn, or pasture.  Because birds can pick up individual particles of bait, birds should be confined outside the treated area during and for at least 24 hours after the bait application.  Exclusion from the treatment area will give fire ant workers a chance to pick up the bait and take it back into their nests (studies have shown that fire ants pick up most of the bait in 12 hours). However, incidental ingestion of baits labeled for sites where birds are free ranging should not harm the birds.  Baits should only be applied during favorable conditions (i.e., greater than 60^oF and optimal at 70 to 90^oF and no rain expected) to ensure fire ants adequately pick up the bait.  To confirm that fire ants are foraging, you can place a few potato chips in the area to be treated.  If the fire ants are found on the chips within 15 minutes, it is a good time to apply fire ant bait.  Alternatively, a bait product can be applied in such a manner to make it unavailable to free ranging poultry, such as applying it around but not inside the pen.  Another alternative is to place bait stations designed for fire ant baits in a grid.  These stations can provide an additional margin of safety, unless a bird breaches the bait station.  If possible choose a bait station that is designed to prevent access by birds.  Be aware that poor fire ant control has been observed with bait stations if individual fire ant colonies dominate the bait stations, excluding workers from other colonies.

More information on applying fire ant baits can be found in Broadcast Baits for Fire Ant Control.

Field Crops and Commercial Vegetables

In cotton and sugarcane production, the fire ant is considered a beneficial insect and fire ant control is not suggested. In cotton fields, fire ants are effective predators of caterpillars and can be sampled using the beat bucket method where the terminals of cotton plants are beaten into a plastic bucket to dislodge insects. In Louisiana sugarcane fields, habitat modification studies have shown an increase fire ant abundance and predation by the ants on sugarcane borers, Diatrea saccharalis (Fabricius). Therefore, fire ant control in sugarcane fields should be avoided to prevent an increase in sugarcane borers and their damage, which will increase pesticide use and counteract sugarcane IPM programs.

Fire ants occasionally feed on germinating seeds and seedlings of corn, sorghum and other field or cover crops, particularly during dry conditions in the spring, sometimes causing stand loss. Fire ants also have been reported to feed on young watermelon, cucumber and sunflower plants, and have damaged peanut and soybean plantings. Okra growers are constantly battling fire ants due to the ants’ attraction to the oils in the plant, nectaries, buds and developing fruit. Fire ant mounds can cause problems in areas where soybeans are not planted on raised beds or rows (i.e., they are flat-planted) because mounds along the rows can be tall enough to interfere with harvesting equipment. During dry periods, the fire ants can chew irrigation tubing, as has been reported in vegetable crops.

Treatment options:

Conventionally-formulated abamectin (Clinch®), pyriproxifen (Esteem®) or  s-methoprene (Extinguish®­) bait products are registered for use in cropland and can be used to reduce fire ants in these areas. However, these baits are slow-acting and must be broadcast-applied several months before maximum suppression is required. Optimum timing of application(s) and economic benefits from control are still to be determined. Use where estimated losses exceed cost of application, and monitor closely for potential secondary pest outbreaks in treated fields.

To prevent injury to corn and sorghum seedlings, neonicotinoid seed treatments (clothianidin, thimethoxam, and imidacloprid) aid in control of fire ants.  An insecticide such as Warrior II (lambda cyhalopthin) or Lorsban®­ 15G (chlorpyrifos) over an open furrow at planting can be helpful where there is a history of stand loss.

Few contact insecticide products are registered specifically for fire ant control in watermelon, sunflower and other crops although some products containing pyrethrins ( Pyrenone® Crop Spray and others) are generally labeled for ant control in these sites. Insecticides  registered  for  other  pests  on  these crops (and known to be toxic to fire ants) are occasionally used to temporarily suppress foraging ants when the crop is threatened.

Fruit and Nut Orchards, Vineyards and Blueberry Plantings

Although fire ants are mostly a nuisance to field workers in these crops, their overall economic and ecological impact remains unknown. In pecan orchards, fire ants prey on pests such as pecan weevils and hickory shuckworms in fallen pecans, but they encourage aphids by preying on their natural enemies. The ants’ nest building aerates the soil of the orchard floor, which is beneficial, but they will feed on the meat of cracked pecans and can damage irrigation systems. Fire ant mounds may interfere with some types of harvesting operations. Chemical control is warranted only if the cost of control is less than the potential economic loss ants may cause. In pick-your-own operations, the liability of ants attacking customers also should be considered.

            Treatment options:

1. S-methoprene bait (Extinguish® Professional Fire Ant Bait) is registered for use in all cropland, and pyriproxyfen (Esteem Ant Bait), abamectin (Clinch® Ant Bait), and metaflumizone (Altrevin®­ Fire Ant Bait Insecticide) are registered in most commercial fruits and nuts.  Optimum timing of application(s)  are still to be determined. Where used, monitor closely for potential secondary pest outbreaks.
2. In pecan and citrus orchards, chlorpyrifos products (Lorsban® Advanced, Lorsban® 15 G, etc.) used to treat the orchard floor will temporarily suppress foraging ants. Spot applications around irrigation systems may be useful to protect equipment from ant damage.
3. Few contact insecticide products are registered specifically for fire ant control in bearing peach orchards, vineyards and blueberry plantings although some products containing pyrethrins (Pyrenone® Crop Spray and others) are generally labeled for ant control in these sites. Insecticides  registered  for  other  pests  on  these crops (and known to be toxic to fire ants) are occasionally used to temporarily suppress foraging ants when damage is observed and the crop is threatened. Turf areas around such plantings can be treated using products registered for use in that site.