Spider Mites – How to Kill and Prevent Spider Mites on Plants

spider mites on leaf

Quick links: What are they? | Identify | Natural Solutions | Chemical Solutions | Prevention | FAQ’s

It could happen to you your plant starts to look a bit odd, fading from bright green to sickly yellow in just a few days. Upon a closer look, it’s clear what is going on – Spider mites!

Subtle, potentially deadly to the plant, and much more common than one would think, these little parasites can sneak their way into your home and infest your favourite plants – and they must be taken care of to keep your indoor garden looking its best. If they aren’t controlled or eliminated, they can spread from plant to plant until they have damaged your whole garden or indoor plant collection, causing unsightly leaf damage or even death to the plant as a whole.

The key is a quick, effective treatment as soon as the problem is discovered.

spider mites yellow and black on leaf

What are Spider Mites?

Spider mites are a type of arachnid – the same class as spiders, scorpions and ticks – but they are very small (even large adults are only 1/50 of an inch, or about the size of the dot on a typed letter i) and not harmful, or even noticed, by humans… until they infest our favourite plants! Adult specimens range from a reddish-brown colour to a pale cream. Younger specimens look much the same as the adults but are of course smaller.

These mites live mostly on the underside of leaves, so they are difficult to detect at first, but since they live in colonies and multiply quickly, their effects are soon noticed. They poke through the underside of leaves and drink out the chlorophyl and other fluids, leaving a light, translucent dot on the top of the leaf. Enough of these little creatures on a leaf and it will dry up, turn yellow, and fall off. One good way to determine if you have an established colony on your plant, is to look for fine webbing around the edges of the leaves.  This is especially common in house plants, but can occur outside too, on strawberries, beans, melons, aubergines, tomatoes, many flowers and even trees.

Spider mites like hot, dry conditions best, so an indoor windowsill with no natural enemies about is a perfect place for them to set up a colony and multiply rapidly. In some cases, a species of plant-feeding mites will be accompanied by a species of mite that feeds on the plant-feeders, creating a miniature food chain, right there on your windowsill!

Spider Mites Life Cycle

Most mites last over winter as eggs, stuck to the leaves and bark of their host plants. They hatch in early spring, when temperatures rise, and leaves begin to turn green. The larvae are very tiny, six-legged creatures that last only a few days before moulting into nymphs, an eight-legged, still tiny version of their adult form. They will moult two more times as they grow, becoming adults after the final moult.

Female spider mites can produce up to 300 eggs in a couple of weeks after reaching adulthood. A new egg can grow to adulthood in as little as five days if conditions are favourable, and the hotter and dryer the weather is, the more prolific they are. A spider mite colony can produce several overlapping generations per year, with some of these new individuals moving from one plant to others by ‘surfing’ on air currents using their webs. It is important to dispose of dead or heavily infested plants carefully, so as to avoid infesting others.

How to Identify Spider Mites on Your Plants

The first sign that you have a problem will be tiny light spots on the leaves, usually yellow or light brown in colour, where the juices had been sucked out of the leaf from below. With more infestation, the leaves will yellow and dry up, sometimes falling from the plant altogether. The plant itself may stop growing.

As the colony establishes itself, you may notice fine webbing around the edges of leaves and between leaves and stem. This is when the problem is spotted most of the time. Shaking the leaves over a sheet of white paper or wiping the bottom of the leaves with a damp tissue, will tell you if there are specimens on your plant. In the first case, you will see tiny dots, like pepper, fall to the paper. In the second case, you will see brown and/or yellow smudges on the tissue.

Damage Caused by Spider Mites

Leaves become spotted and yellow, often dry, and may fall off of the plant altogether. This is due to the juices being sucked out of the underside of leaves by the spider mites. The loss of leaves and productivity within each leaf may cause a significant decrease in yield for watermelon, melon, and squash varieties. Plants such as beans and sugar peas can see damage on the actual pods as well. Spider mite damage is otherwise mostly cosmetic, though it can kill certain plants and is of obvious concern around plants grown for appearance, such as field roses, house plants, etc.

large plant with spider mites

Natural Solutions to Spider Mites

If you prefer not to use harsh chemicals on your plants, there are plenty of environmentally-friendly options open to you. Nature has its own way of limiting the spread of these little mites, so all we have to do is let nature have access to them, or give nature a little help, and the problem can be curbed.

Using Predators (the biological method)

Lacewings, thrips, ladybirds and even some other mites (such as Phytoseiulus persimilis) can greatly reduce the size of spider mite colonies, though they seldom wipe them out entirely. Using pesticides will reduce these natural predators and allow spider mite populations to increase unchecked, as they will move in as soon as the chemical has sufficiently diluted and can produce a thriving colony very rapidly. Regular, appropriate watering and use of mulch is also beneficial to keeping plants strong and better able to fight off the negative effects of infestations.

Predatory mites and insects for indoor plants can be ordered online. These can eat hundreds of mites in a day and are not dangerous or unsightly to people, plants or pets.

Using Essential Oils

There is some indication that chamomile, coriander, spearmint and rosemary oils are effective at killing the two-spotted variety of spider mite eggs and adults. A few drops in a spray bottle of water, sprayed onto the leaves, is the best method of application. Neem oil sprayed onto the leaves will also show some success in suffocating dust mites.

Get Them Hot Under The Collar

Hot pepper extracts sprayed onto plants showed some success. Bell pepper, jalapenos, chile and cayenne pepper extracts killed about 45% of mites in test conditions, and have been shown to reper mites prior to infestation.

Speculative Home Remedies

Three tablespoons of dish soap in a gallon of water is a high enough concentration to kill dust mites without being so high as to harm your plants. Spray this onto infested plants weekly, and rinse after a few hours.

Rubbing alcohol, applied to the leaves with a cotton wipe, can also kill spider mites. It is also recommended to rinse the leaves afterward with a water wipe.

In outdoor situations, spraying with a hose can physically remove many spider mites from a plant, but they will likely come back very quickly, and may be aided in spreading to other plants in this way.

spider mites webs

Using Chemicals

Pesticide Sprays

In order to properly apply pesticide sprays, you should invest in a professional lance sprayer. These are not overly expensive, and do a very good job of helping you get into hard-to-reach areas of the plants, and keeping the spray more contained to desired areas.

Be sure to cover the top and bottom of leaves evenly. Most eggs and mites will be on the underside of the leaves, but they can also escape danger by moving topside, so it is important to do both areas. Spraying when the lights are off is recommended, as the mites will be more active. Using a dimmer or a headlamp will help you be able to see what you are doing in such conditions.

Make sure there is good air flow through the room of area you spray, to prevent rot and other negative effects.

Fumigate with Vapourised Sulphur

Vaporised sulphur is very effective at killing and repelling a number of pests, including spider mites. It is best used in a grow room or other isolated growing situation, rather than in the home for houseplant care.

The vapour of this substance prevents the mites from feeding or reproducing properly, dropping populations very quickly.

Do not use it during the last two weeks of flowering.

How to Prevent Spider Mites in the First Place

Even better than killing off an already-established spider mite colony, is preventing the infestation in the first place. If you’ve just gotten rid of a colony, you’ll also want to prevent another from moving in and taking its place.

When you bring a new plant into your home, check for mites by placing a white paper underneath the leaves and tapping them to check for mites. You can even do this before purchasing the plant.

When you have the plant at home, with no sign of mites falling onto the paper at the shop, place it away from open windows or vents, as this is often how the spider mites enter and infest a new plant. Dusting leaves once a week can also keep new colonies from starting.

Spider mites prefer dry conditions, so keeping your plants well-watered is also beneficial.

Spider Mite FAQ’s

Is it better to get rid of the infected plant?

If an infestation is advanced and has caused a lot of damage to a plant, it may be most effective just to rid yourself of the plant altogether. You should then apply preventative measures to your other plants, especially in the vicinity where your infested plant was.

How long does it take to get rid of spider mites?

Even for infestations that are not considered severe, it may take three or more weekly applications to take care of the problem. Of all of the methods, predatory mites is probably the quickest, as these consume hundreds of mites a day and there is no need to reapply or wait for concentrations to fade – they work for you all day long, every day.

What are the most common plants infested by spider mites?

Spider mites are not picky eaters. They will live and thrive on hundreds of plant varieties. In the outdoors, they like melons, strawberries and fruit trees, and indoors they prefer ornamental flowers and shrubs.

Enjoyed that? Good!

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