Ants are a common sight on various plants, from garden shrubs to indoor potted herbs, and their presence is typically a sign of a deeper pest problem. These small insects are not usually feeding on the plant itself but are instead protecting colonies of sap-sucking pests, such as aphids or mealybugs. Successfully eliminating ants requires a two-pronged approach: immediate removal of the visible pests and colony, followed by long-term strategies to discourage their return. The methods used must be safe for the plant species while effectively disrupting the ant-pest partnership.
Understanding the Ant-Plant Relationship
The presence of ants on foliage is a classic example of a mutualistic relationship, often described as “farming.” Sap-sucking insects like aphids, scale, and mealybugs feed by piercing plant tissue and extracting phloem sap, which is rich in sugar. They excrete the excess sugar as a sticky, sweet waste product known as honeydew. Ants are highly attracted to this honeydew, which serves as a significant food source for their colony. In exchange for the sugary droplets, the ants actively tend to these pests, moving them to new, healthy parts of the plant and aggressively defending them from natural predators. This protection allows the sap-suckers to reproduce unchecked, leading to increased plant damage. Therefore, permanent ant removal requires addressing the underlying pest infestation first.
Immediate Removal Methods for Infested Foliage
For plants with a visible ant or pest presence, physical and localized chemical treatments offer the fastest solution.
Water Spray
A direct, forceful spray of water from a garden hose or sink nozzle can physically dislodge both ants and the soft-bodied pests they are protecting from the stems and leaves. Focus on the undersides of the leaves, where many pests like to congregate. Use a pressure setting that will not damage the plant tissue.
Insecticidal Soap
For a more thorough treatment, an insecticidal soap solution works on contact by disrupting the pests’ cell membranes and dissolving their protective waxy outer coating. A simple solution can be made by mixing one tablespoon of pure liquid Castile soap with one quart of water. This mixture must be applied thoroughly to all surfaces, including the trunk and the soil surface, as it only kills insects that it directly contacts.
Neem Oil
Another effective surface treatment is neem oil, which functions as both a repellent and a growth disruptor. Neem oil contains azadirachtin, a compound that interferes with the hormonal system of insects, hindering their ability to feed, breed, and communicate. A typical horticultural application involves mixing four teaspoons of neem oil and two teaspoons of liquid soap per gallon of water. Apply this during cooler times of the day to prevent leaf burn. Consistent reapplication every seven to ten days is necessary to break the pest life cycle entirely.
Eliminating the Colony Source
Surface treatments address the immediate issue, but achieving long-term control requires eliminating the ant colony itself, which is the source of the foraging workers. The most effective method for colony destruction is the strategic use of ant baits.
Ant Baits
Baits consist of an attractive food substance, like sugar or protein, mixed with a slow-acting insecticide. The slow nature of the poison is intentional, allowing foraging worker ants to consume the bait and carry it back to the nest before they die. The contaminated bait is then shared with nestmates and, critically, the queen. When the queen is eliminated, no new workers are produced, and the colony collapses within a few days to a couple of weeks. Liquid or gel baits are often preferred as they mimic the honeydew the ants are seeking. Placement must be along ant trails and away from direct contact with the plant’s roots.
Diatomaceous Earth (DE)
Another option, particularly for colonies nesting in the soil near the plant, is food-grade Diatomaceous Earth (DE). This fine powder is composed of the fossilized remains of diatoms. To an insect, the particles physically cut through the waxy outer layer of the ant’s exoskeleton. This mechanical action causes the insect to rapidly lose internal moisture and die from desiccation. DE must be applied as a dry, thin layer around the base of the plant or directly into the nest entrance to be effective.
Long-Term Prevention Strategies
Once the immediate infestation and the main colony are addressed, preventative measures are necessary to stop re-infestation. Creating a physical barrier prevents ants from climbing up the trunk or stem to reach the foliage. A sticky barrier product, such as horticultural tree banding adhesive, can be applied to a non-porous band wrapped around the plant’s trunk or the rim of a container. This tacky barrier traps any crawling ants attempting to ascend the plant, effectively severing their access to any new sap-sucking pests. Apply the adhesive to a wrap rather than directly on the bark, as the oil in the product can cause damage to young trees. Regular inspection of the barrier is necessary, as dust or trapped insects can create a bridge for subsequent ants to cross. Maintaining optimal plant health also plays a significant role in prevention, as stressed or weakened plants are often more susceptible to pest pressure that attracts ants.