Red spider mites (Tetranychus urticae) are a common and destructive group of plant pests often referred to as two-spotted spider mites. They are technically arachnids, related to spiders and ticks, and cause damage by feeding on plant cells. This article provides practical steps for identifying, eradicating, and preventing these pervasive pests from taking over your plants.
Identifying Red Spider Mite Infestations
The red spider mite is extremely small, with adult females measuring only about 0.4 mm long, making them barely visible. They are typically yellowish-green with two distinct dark spots, though they can appear reddish-orange when overwintering. Confirmation often requires a magnifying glass or a simple “tap test” on white paper.
The most recognizable damage sign is a fine, pale stippling on the upper surface of leaves. This speckled pattern occurs where the mites have pierced plant cells to suck out the contents. As the infestation worsens, leaves may turn yellow or bronze and drop prematurely. The mites produce fine, silky webbing, typically found on the undersides of leaves and between the leaf and stem, which they use for protection and movement.
Immediate Non-Chemical Removal Methods
Once an infestation is identified, physical removal is the first line of defense to rapidly reduce the population size. Immediately isolate the infested plant to prevent spreading. Use a strong, direct jet of water, such as a sprayer or shower head, to physically dislodge the mites from the leaves and stems. Spray the undersides of the leaves thoroughly, as this is where the mites prefer to congregate and lay their eggs.
Following the initial rinse, apply a contact-killing solution like insecticidal soap or horticultural oil. Insecticidal soap works by penetrating the mites’ outer layer, causing dehydration and death. Horticultural oils, such as neem oil, smother the mites and their eggs by creating a thin film over their bodies.
These contact treatments must be applied to every surface of the plant, especially hidden parts where the mites hide and webs are dense. Since neither soap nor oil provides long-term residual protection and they do not kill all life stages effectively, repeat applications are necessary. Mite eggs can hatch quickly, so a follow-up treatment every five to seven days for at least two weeks is recommended to break the life cycle. Always apply these sprays in the evening or on a cloudy day to prevent the oil from magnifying sunlight and causing leaf burn.
Utilizing Advanced and Biological Controls
For severe or persistent infestations that do not respond to simple contact sprays, advanced strategies are necessary. One option is the use of commercial miticides, which are specialized chemical controls designed to target mites. Because spider mites reproduce rapidly and can develop resistance to a single chemical, it is important to rotate between miticides that have different modes of action.
Some miticides, known as translaminar products, are absorbed by the leaf surface. They create a toxic reservoir inside the tissue, which helps to kill mites feeding on the undersides of leaves. When using contact miticides, thorough spray coverage is essential for success. Always follow the manufacturer’s instructions and apply each product two to three times, separated by a 7 to 10-day interval, before switching to a product with a different chemical class.
A second advanced approach involves biological control, which is the introduction of natural predators like the predatory mite Phytoseiulus persimilis. This predator is highly effective because it feeds voraciously on all life stages of the two-spotted spider mite and can navigate the protective webbing. P. persimilis performs best in warm conditions with relative humidity above 65%. Biological control is often a preferred solution for indoor or greenhouse environments where conditions can be controlled, and it should be applied as an active treatment rather than a preventative measure.
Preventing Future Mite Outbreaks
Long-term management focuses on manipulating the environmental conditions that favor mite proliferation. Spider mites thrive in hot, dry conditions, with outbreaks often occurring when humidity is below 50%. Increasing the ambient humidity around susceptible plants, such as through a humidifier or pebble trays, can make the environment less hospitable for the pests.
Regularly inspecting plants is an effective preventative measure, especially checking the undersides of leaves where mites hide. A proactive routine of wiping down smooth-leaved plants with a damp cloth or a dilute neem oil solution can physically remove early-stage mites and eggs. Finally, every new plant should undergo a quarantine period of at least two weeks to ensure it is pest-free before being placed near established plants.