Spider Mites: How To Identify And Get Rid Of Them

What Are Spider Mites?

Spider mites are arachnids in the Tetranychidae family. Despite their less than a millimeter size and seemingly harmless appearance, they can compromise the health of over a hundred commercial crops. Pests thrive in hot and dry climates, which allow them to reproduce rapidly. The two-spotted spider mite, one of the most common species, can cause problems in agricultural fields, orchards, and greenhouses worldwide.

These arachnids use their needle-like mouthparts to pierce individual plant cells and feed on the vital sap within. The damage occurs as the arachnids move from cell to cell, leaving behind a trail of destroyed tissue that disrupts the plant’s ability to photosynthesize properly. One telltale sign of pests is the fine webbing they produce, which serves as both protection for their colonies and a transportation system for moving between feeding sites.

How Do Spider Mites Spread And Affect Plants?

These barely visible pests multiply fast and damage crops by feeding on their leaves. Knowing how they spread and spotting signs early can save growers from serious crop losses.

Life Cycle Of Spider Mites

Their remarkably rapid development from egg to adult spans just 5 to 20 days. Where do spider mites come from initially? In most regions, they overwinter as adults or eggs, emerging from protected winter shelters as temperatures rise in spring.

The arachnid progresses through four distinct life stages:

• Eggs. They appear as transparent spheres on leaf undersides, hatching within 3 days when conditions are optimal.
• Larvae. The newly hatched, six-legged larvae immediately begin feeding on plant tissue, remaining in this stage for 2–3 days.
• Nymphs. During this phase, arachnids develop eight legs and progress through two stages — protonymph and deutonymph.
• Adults. Reaching adulthood marks the beginning of reproduction (about 20 eggs daily by an adult female).

This efficient life cycle explains why the populations can expand so rapidly. A single female’s ability to produce hundreds of spider mite eggs during her lifetime, combined with the quick development of her offspring, creates the potential for exponential population growth.

What Are The Signs Of Spider Mite Infestation?

The early sign of spider mites to look for is pale discoloration spots on the leaves. As the pests multiply, they produce fine silk webbing that covers leaves and stems.

Look for these tell-tale signs to confirm spider mite infestation:

• yellowing or bronzing of leaves, especially on the upper surface;
• tiny moving dots visible under magnification, particularly on leaf undersides;
• silk webbing between leaves and along stems;
• stunted plant growth and curling leaves.

What Damage Do Spider Mites Cause?

Typically, these pests can lead to 6–10% crop loss, but during severe infestations, losses easily climb to 14% or higher ^{Uygun, T. et al. (2020, November 3). A new approach to monitor and assess the damage caused by two-spotted spider mite. Experimental and Applied Acarology, 82, 335-346. https://doi.org/10.1007/s10493-020-00561-8.}. Spider mite damage starts on leaves, first dotted, then taking on a bronze or silvery appearance and becoming brittle.

The spider mites leaf damage triggers a cascade of problems. When these pests feed, they reduce chlorophyll content and disrupt vital plant processes, including photosynthesis, carbon dioxide absorption, and transpiration. Affected plants might suffer from:

• desiccation and premature leaf drop;
• reduced yield production;
• increased susceptibility to fungal and bacterial crop diseases;
• crop failure in the most severe cases.

Inspect crops weekly for early signs of pests’ activity, such as fine webbing or stippling on leaves, and swiftly apply treatments to avoid arachnids from spreading.

How To Prevent Spider Mite Infestations

Measures to prevent spider mites work best when integrated into daily farming practices. A systematic approach to prevention helps maintain crop health and reduces the need for reactive treatments.

Here’s your toolkit to keep spider mites away:

• Grow resistant varieties. Opt for crop varieties with documented resistance to the pest.
• Adjust operations to the weather. Track hot and dry weather and respond with timely irrigation and shading during these high-risk periods.
• Maintain soil moisture. Well-hydrated plants better resist pest pressure. Install drip irrigation systems to ensure consistent moisture levels while conserving water.
• Sanitize tools. Keep equipment clean between field operations. Regular cleaning reduces the risk of spreading pests across growing areas.
• Encourage natural predators. The presence of natural enemies helps maintain arachnid populations below damaging levels.
• Avoid using high-nitrogen fertilizers. Nitrogen overuse can make crops more susceptible to the pest. Consider slow-release or organic fertilizer options.

The Disease risk feature in EOSDA Crop Monitoring helps prevent pest infestations. It analyzes weather conditions, combines this data with the crop’s growth stage, and predicts the chance of spider mites or other major pests appearing on any given day over the next two weeks.

How To Get Rid Of Spider Mites In Your Fields

Spraying pesticides isn’t enough to solve the pest problem in commercial fields. Successful growers watch their crops closely and use integrated pest management (IPM) — a mix of cultural, biological, and other methods to kill spider mites while cutting back on harsh chemicals.

Cultural Control

Cultural methods are essential for managing infestations in agricultural fields. These non-chemical control methods focus on creating unfavorable conditions for pests and enhancing plant resilience.

Since spider mites prefer dry conditions, treating them involves managing irrigation. Maintain higher humidity around plants through regular watering and/or misting to deter pests. Plus, regular watering helps remove dust (favorable for pests) from leaves and stems.

Crop rotation is another key strategy. Changing crop types from season to season disrupts the spider mite life cycle and lowers the chance of recurring infestations. The Crop rotation feature in EOSDA Crop Monitoring simplifies this process, enabling farmers to plan and track anti-pest rotations efficiently.

Using the Scouting feature of EOSDA Crop Monitoring, growers can now send scouts straight to problem areas, which eliminates the need to traverse every row in search of tiny pests. This farm management solution allows agricultural cooperatives and large-scale crop producers to save time and address issues through cultural measures while still small.

Biological Control

Biological spider mite treatment relies on natural predators. Phytoseiulus persimilis and Neoseiulus californicus are commonly used predatory mites for controlling arachnids. Other biological control agents include lacewings, Stethorus spp. (mite-feeding ladybirds), and Feltiella spp. (predatory gall midges).

A rule of thumb is to have one predator for every 10 pests to ensure effective crop protection. Multiple releases may be necessary to rapidly reduce pest populations. It’s also a good idea to limit the use of broad-spectrum pesticides that target all insects, including helpful ones. A diverse field environment can naturally keep pest populations under control.

Natural Control

Often, it is possible to get rid of spider mites naturally through:

• Syringing. Wash the tiny pests away from leaves while saving natural predators’ populations ^{Shetlar, D. J. (2011, September 20). Spider Mites and Their Control. Ohio State University.}.
• Neem oil. To kill spider mites on contact, mix neem oil with water and spray it on infested plants during cooler times of the day, ensuring thorough coverage of leaf undersides.
• Insecticidal soap. Sprayed on the plants, it breaks down the arachnids’ exoskeletons, causing their dehydration and death.
• Herbal solutions. Though not widely used, some herbal solutions, such as a mixture of cinnamon, cloves, and tea, can be used to repel arachnids in conjunction with other natural methods.

Chemical Control

Chemical control of spider mites is most effective when used within an IPM framework, as a last resort after other methods have been tried. Consider these options:

• Miticides (selective pesticides). As their name implies, these treatments work specifically against mites. For best results, rotate between different active ingredients such as Abamectin, Bifenthrin, Hexythiazox, and Spiromesifen to prevent the pests from developing resistance.
• Sulfur treatments. Sulfur helps get rid of spider mites on many vegetables and ornamental plants, but you should keep it away from sensitive ones like cucumbers and melons. It is a skin irritant and requires caution during application.

By weaving these practices into your farming routine, you create a defense system against spider mites that works around the clock.