Spider Mites - A Comprehensive Guide

As indoor gardeners, we’re always looking for ways to cultivate our plants in the best possible environment. However, there is one tiny pest can wreak serious havoc on your crops, leaving you frustrated and struggling to keep them healthy. That pest is the two-spotted spider mite (Tetranychus urticae), a hard-to-spot yet notorious invader that can quickly decimate your plants if left unchecked.

In this post, we'll dive into the biology of these pesky mites, their life cycle, and how to spot and manage an infestation before it spirals out of control. Whether you’re a beginner or an experienced grower, knowing how to spot and deal with spider mites is essential for maintaining a thriving indoor garden.

The two-spotted spider mite, as its name suggests, has two distinctive dark spots on either side of its body, which is usually a yellowish or greenish hue. This microscopic pest is part of the arachnid family, making it closely related to spiders and ticks. Despite their small size (roughly the size of a pinhead), they are destructive due to their feeding habits. Due to their extremely small size, it's generally not possible to positively identify spider mite without optical assistance. You'll need a magnifying loupe in order to see them in sufficient detail for identification.

Spider mites are sap-suckers. They pierce the plant’s cells with their needle-like mouthparts and suck out the cellular contents. This feeding damages the plant tissues, leading to a variety of symptoms such as yellowing, stippling, and sometimes leaf curl or deformities. Over time, this weakens the plant, making it more susceptible to disease and reducing its overall vitality.

One of the trickiest aspects of managing two-spotted spider mites is detecting them early on. Due to their small size, they’re often hard to spot with the naked eye. Here’s what you should look for:

Yellowing or stippling of leaves: The most noticeable sign is tiny yellow or silver speckles on the leaves, caused by the mite feeding on plant cells.

Webbing: As the infestation intensifies, spider mites produce fine webbing on the undersides of leaves or around the plant. This is one of the most telling signs of an advanced infestation.

Leaf drop or deformation: Over time, heavily infested plants may start to lose leaves or exhibit deformities like curled, dry edges.

If you’re unsure, you can use a magnifying glass to closely inspect the undersides of your leaves, where the mites prefer to congregate.

Two-spotted spider mites undergo a simple life cycle that includes an egg, larval stage, protonymph, deutonymph, and adult. The entire cycle can be completed in as little as five to seven days under optimal conditions (around 30°C or 86°F), which is why these mites can multiply at an alarming rate.

Females lay eggs on the undersides of leaves, and within a couple of days, the larvae hatch. They then proceed through their nymphal stages before reaching adulthood. Each adult female can lay up to 100 eggs in her lifetime, making it easy for an infestation to grow exponentially. Below is an extreme example, demonstrating the potential for spider mite populations to multiply drastically over a 4 week period.

Assuming that conditions are perfect and no predators or interventions occur, here's a rough breakdown of how population growth could unfold:

Day 1: A single pregnant female mite finds its way into your grow room.

Week 1: That female lays eggs, and within about 5-7 days, those eggs hatch. By the end of the first week, you'll have a population of roughly 20-30 mites, assuming each egg hatches and survives.

Week 2: The new mites mature into adults and begin laying eggs. Now, you could have 20-30 adult females, each laying 20-30 eggs per day.

Week 3-4: This cycle continues, and by the end of week 4, the population can grow exponentially, potentially reaching several thousand mites or more.

Depending on factors like food availability and space, it's reasonable to expect a population in the range of 10,000-20,000 mites by the fourth week, assuming optimal conditions and no limiting factors.

So, after 4 weeks of undisturbed growth, starting with just one pregnant mite, you could easily end up with a population in the thousands, making spider mite infestations spread quickly and potentially devastate crops if not controlled early on.

Fortunately, you’re not alone in the battle against two-spotted spider mites. There are several natural predators that can help keep their numbers in check, with the most effective being:

Phytoseiulus persimilis predatory mites. This fast reproducing voracious predator is aguably the most effective predatory mite species, being primarily suited to dealing with two spotted spider mite. It will however struggle in drier conditions, making them less suitable for flowering/fruiting stages that require lower humidity.

Amblyseius californicus predatory mites. These mites are highly effective at hunting down and consuming a broad range of spider mites species, including red spider mite and broad mite. however they have a longer life cycle than Phytoseiulus persimilis

Both species of these beneficial mites can be purchased and introduced into your grow room.

Prior to applying chemical control to your plants, it's a good idea to physically remove as many mites as possible. Here are a few options:

Water spray: Use a strong jet of water to knock the mites off the leaves. Make sure to focus on the undersides of the leaves, as this is where they typically reside. Repeat this process every few days to reduce the population. If you've not got easy access to an external faucet, our High-Pressure Manual Watering Kit will solve that.

Pruning: If only a few leaves are affected, removing them can help limit the spread of the infestation. We have a wide range of quality pruners available for this.

Vacuuming: Use a handheld vacuum or shop vac with a soft nozzle attachment to gently suck up the mites from the leaves, especially the undersides where they tend to hide. Be sure to not use a vacuum cleaner that is too powerful and hold the nozzle close to the leaves without touching them too roughly, as this could damage the plant. This method can be repeated every couple of days to significantly reduce the mite population.

If the infestation is severe, you might need to turn to chemical treatments. Be sure to use these cautiously and follow the instructions on the label to avoid harming your plants or yourself. Here are a few common options:

Insecticidal soap: These soaps suffocate the mites and can be applied directly to the plants. It’s a relatively gentle solution that’s safe for most plants. Skram Pest Prevention and Skram Plant Wash are two great insecticidal soap-based products. They're also safe for use on consumable crops.

Horticultural oils: These oils, such as neem oil or insecticidal oils, coat the mites and prevent them from feeding. They can also be effective in smothering eggs. Dr Hydro - Spider Mite is an effective product that utilises these oils for effective spider mite control.

Miticides: There are specific miticides formulated to target spider mites. However, it’s essential to rotate between different products to avoid resistance developing. Dr Shimmel Organic Spider Mite Terminator is a highly effective organic miticide that has the power to deal a devistating blow to spider mite populations. Visit us in store to discuss and view all available miticides and sprayers.

Permethrin-based smokers: These quick and easy-to-use smoke bombs provide an immediate, hard-hitting blow to adult mite populations. Guard 'n' Aid Smoke Bomb Insect Killers are available in a range of sizes to suit all growing scales.

Sulfur smoke: Because sulfur is toxic to spider mites, applying sulfur smoke within your grow room is highly effective at reducing bug populations, especially in larger areas. Several applications over a number of nights are recommended in order to achieve maximum effectiveness. Hotbox Sulfume is the market leading sulfur smoke product and has been a top choice for horticulturalists for many years.

If you've come across an infestation and need to deal with it quickly and effectively, we recommend using a combination of physical and chemical control methods. Thorough applications of water jet and/or vacuuming can reduce the current adult populations by over 90%, with a series of follow-up smoke and spray applications eradicating residual adult populations and hatchlings.

It's also important to be aware that many chemical and smoke products are not suitable for use on consumable crops, and spider mite resistance can also build to these over time. Using a combination of products while also considering crop type and harvest timescales will help you to achieve the safest and most effective solution to your spider mite problem, with physical removal always being the preferred first step in any eradication program.

Prevention is always better than cure. To keep two-spotted spider mites from entering your grow room in the first place, consider the following steps:

Inspect new plants: Always thoroughly inspect any new plants before bringing them into your grow space. Look for signs of pests and quarantine new arrivals for a week or two.

Install Barriers: Spider mites can often make their way into your indoor grow room by themselves, especially if the room is situated near the outdoors. Ensuring that you have an airtight space with minimal points of entry can be half the battle. This is where a quality grow tent shines. Combine this with a bug barrier on your intake ducting and you'll drastically reduce the chances of spider mite being able to find their own way in.

Maintain good hygiene: Regularly clean your grow room, as spider mites can hitch a ride on equipment or clothing. Wipe down surfaces and disinfect tools to avoid contamination.

Replace equipment: Some grow room equipment - especially bamboo canes and fabric pots - can be a haven for spider mite and allow them to return on subsequent grows. Replace them aftern an infestation to reduce the chances of them returning.

Control environmental factors: Mites prefer warm conditions, so maintaining lower temperatures and good air circulation can help deter them.

Use sticky traps: Placing yellow sticky traps in your grow room can help catch adult mites before they have a chance to establish an infestation.

The two-spotted spider mite is a resilient and fast-breeding pest that can cause significant damage to indoor plants if left unchecked. However, with vigilance, early detection, and a combination of physical, chemical, and natural solutions, you can keep these mites at bay and protect your garden. Regular inspections, good hygiene, and prevention tactics are your best defence in ensuring that spider mites don’t take over your grow room.

By understanding their biology, recognising the signs of an infestation early, and employing effective control methods, you’ll be well on your way to keeping your indoor garden healthy and thriving. Happy growing!