Prepared by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University. (New 08/10.)
Fire ants can be a nuisance in the vegetable garden. In addition to being a stinging insect, they can damage some vegetable crops, such as okra and Irish potatoes. Occasionally they may feed on tender seedlings of corn, cucumber and watermelon.
A vegetable garden that is frequently tilled may have fewer fire ant mounds because tilling disturbs the fire ants and causes them to move. However, some mounds will persist, such as those that are too close to the individual vegetable plants to adequately be disturbed by tilling, or in gardens that are heavily mulched for weed control. In these cases fire ant baits or mound treatments may be necessary.
Fire ant mound in mulched area of vegetable garden
Joey Williamson ©2010 HGIC, Clemson Extension
If fire ant baits are applied during the spring and fall to the lawn area surrounding the garden, this may significantly control fire ants within the garden site (see EIIS/TO-6 Fire Ant Management in the Home Lawn). Besides treating for fire ants in the surrounding lawn, some fire ant baits and products for mound treatments also are labeled for use within the vegetable garden for additional control. Always read the product label for where and how it can be safely used. The label must state it is for use around the specific vegetables being grown, and state it is for fire ant control as a bait or drench application.
Some fire ant baits can be used both within the garden and on the lawn. These include baits containing the active ingredients spinosad and pyriproxyfen. Spinosad is a natural metabolite product produced by a soil microorganism (Saccharopolyspora spinosa) and affects the ant nervous system. Many of the spinosad products are even approved for organic vegetable production. Baits containing spinosad are relatively fast-acting, and this makes them a good choice for controlling individual mounds that occur in the garden itself.
Pyriproxyfen is an insect growth regulator that mimics the effects of the insect’s own juvenile hormone, reducing the production of viable eggs. Although pyriproxyfen prevents the development of more worker ants, it does not kill existing adults. Because of this, ant colonies may persist up to several months after treatment, until worker ants present at the time of treatment die naturally.
For the quickest control, gardeners should not wait until fire ant mounds become large, but should apply one of these baits as soon as fire ants are observed in the garden. Be sure to treat the lawn area around the outside of the garden with fire ant bait as well. Worker ants from mounds located in the garden will readily forage for food many feet into the nearby lawn area.
For individual mound treatments with baits, do not put the bait directly on top of the mound, but sprinkle it around each mound. Baits are best applied in the spring and fall when temperatures are moderate (70 to 75 ºF). Apply baits in late afternoon or early morning when the ants are actively foraging. To determine if fire ants are foraging, crumble a few potato chips and place them on the ground beside a mound. Check for ant activity in about 30 minutes. If the colony is actively foraging, ants should be noticed carrying small pieces of the chips back to the mound. For best control, always use fresh bait.
If baits are to be applied to larger areas, use a handheld seed spreader for even distribution. Apply baits when there is no threat of rainfall within 24 hours, as rain will dissolve the bait granules. Likewise, do not apply the bait onto wet grass. In the garden, the use of a drip irrigation system or soaker hoses will reduce the amount of soil that becomes wet, and therefore will be less apt to dissolve the granular baits applied.
Examples of granular fire ant bait products containing spinosad with labels for use within the vegetable garden:
Example of fire ant bait product containing pyriproxyfen with label for use within the vegetable garden:
You can use a liquid drench to eliminate large mounds that need to be controlled quickly, but be sure to use an insecticide labeled for use in home vegetable gardens. Some insecticide products commonly used in home vegetables include label directions for mixing and applying the product as a mound drench. Products containing the active ingredient spinosad are quite effective as mound drenches, and insect sprays with this active ingredient may be used to control many other pests in the home vegetable garden. Mound drenches are relatively quick-killing. Check product labels for specific directions. Spinosad can be applied near most vegetable crops for fire ant control.
Examples of liquid insecticide products containing spinosad with labels for use within the vegetable garden:
Use a watering can, sprinkler can, or bucket to mix and apply the drench. Read the label, mix the specified amount of insecticide in water, and pour over the mound. To be successful using an insecticidal drench, enough water must be applied to thoroughly soak the mound. Depending on the size of the mound, this ranges from one to two gallons of pesticide solution. First apply about ¼ of the total volume in a circle about 12 inches from the outside of the mound. This may prevent the queen or workers from escaping through their underground network of tunnels. Then apply the rest of the drench directly onto the mound. When applied properly, mound drenches will eliminate a mound within a few hours.
A supplemental label of one carbaryl product (GardenTech Sevin Concentrate Bug Killer) was found that allows for fire ant control by mound treatment around vegetable crops listed on the label. Mix ¾ fluid ounce of product per gallon of water, and apply in a manner as stated for products above.
Some brands of carbaryl dust may be sprinkled over the fire ant mounds within the garden. Check the product label for mound treatment directions. Some fire ant control will be obtained, but the remainder of the colony may move to another site.
Note: Never use products containing acephate for mound treatments in the vegetable garden (such as Hi-Yield Acephate Fire Ant Killer, Ortho Orthene Fire Ant Killer, or Surrender Fire Ant Killer). Acephate can be used to treat fire ant mounds in home lawns, but it is not for use around vegetable plants. It is a systemic insecticide that is readily absorbed by plant roots and will move up into leaves and fruit of vegetables. Permethrin is listed for use as a spray insecticide on some vegetables, and the labels of some products will mention fire ant control as a drench. However, the labels do not specify that the products can be used as a drench within the vegetable garden.
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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.