How to Get Rid of Spider Mites on Weed Plants

Sophia Delphi May 11, 2022 - 9 min read
Fact Checked
A colony of spider mites with web on a weed plant

Home gardening can be incredibly rewarding.

Spending time in the fresh air, carefully tending your crops and watching them grow from tiny seedlings into mature, productive plants — and of course, enjoying the delicious fruits of your season’s worth of labor.

[Sounds of brakes squealing]

All of that enjoyment can come to a screeching halt the moment that pests show up in your garden. An invasion of aphids, beetles, moths, and slugs will quickly take the joy out of gardening.

The problem isn’t limited to people growing tomatoes, peppers, and strawberries in their backyard. It’s also an issue for those who’ve lovingly planted and nurtured weed plants.

And it doesn’t just affect outdoor cannabis gardens. Pests can be an issue for indoor growers as well.

The biggest enemies they face are spider mites. Let’s learn more about them and how to get rid of them.

What Are Spider Mites?

There are numerous species of these tiny predators, but “two-spotted” spider mites [1] (often called TSSM) love to feed on cannabis plants.

To be honest, they feed on hundreds of different types of plants, including fruits, vegetables, flowers, and shrubs, but that knowledge isn’t any comfort to weed lovers who are trying to grow their own supply.

These mites are distant relatives of spiders and ticks, but they do much more damage to crops. They proliferate and attack in hot, dry weather, piercing leaves and sucking on the chlorophyll and sap inside.

That feeding leaves small yellow or white spots on the leaves, giving them a mottled appearance at first. Eventually, the plants may look bleached, leaves will fall off — and the plants will eventually die. Once the spots proliferate on leaves, the leaves can’t be saved.

Worst of all, spider mites are prolific. The female mites in a colony can lay millions of eggs in a month. The eggs hatch in just three days, and less than a week later, all of that new generation has reached sexual maturity and is ready to reproduce.

There’s even more bad news: two-spotted spider mites are resilient. They adjust quickly to any substance used to fight them, particularly insecticides, and the mites that survive become immune to those treatments.

So even though spider mites are tiny, smaller than 1/20th of an inch in size, they can quickly overrun a cannabis grow and destroy it.

How to Recognize Spider Mites

Needless to say, it’s crucial to recognize spider mites [2] as soon as they appear on your plants and deal with them quickly. In just days, they can be almost impossible to eradicate, and particularly bad infestations can kill a plant overnight.

With the naked eye, it’s almost impossible to see these mites. If you’re lucky, they’ll look like tiny spots no bigger than the tip of a pencil.

With a magnifying glass, you can tell a two-spotted spider mite by the — you guessed it — two spots on their backs. The spots can be red, green or tan. It’s even harder to discover the mites’ eggs; they’re round and clear, but each is only 1/400th of an inch in size.

That means the best approach is to inspect plants at least once per day for any damage. Those white or yellow spots left on the undersides of leaves by the mites’ teeth could be the first sign that two-spotted spider mites have infiltrated your grow.

Even so, the spots are difficult to see until the pests may be too numerous to fight. It’s easier to look for other signs of an infestation.

When spider mites lay eggs, they spin a web to protect them. During your daily inspection, look carefully for very fine white threads running across or between the leaves. They’re a clear sign you have a problem. You might also see your plants taking on a dirty or dusty look; that’s because the webs collect dirt and dust.

In short, spider mites are an extremely serious threat to your crop, and you have to act quickly if you discover them.

How to Fight Spider Mites on Weed Plants

The first step in fighting spider mites is to be proactive. Growers often import two-spotted spider mites into their garden or grow room inadvertently.

Proactive Protection Measures

Growing from seed is your best defense. Any clones or plants you’ve acquired elsewhere should be quarantined for at least two weeks and closely examined daily until you can be sure they aren’t infested. This is particularly important if you have an indoor grow since the best defense against these mites is to keep your growing space “clean.”

Grow rooms require additional protection measures. A key one is making sure you’re clean before entering the room; it’s best to change your clothes if you’ve been outside since the mites can easily hitch a ride on you. If the room opens to the outdoors, be careful; spider mites can even blow in on a gust of air.

Also, keep pets out of the grow room, install ventilation filters that will keep bugs out, keep the temperature as low as possible and the humidity as high as possible (without damaging the growing conditions), regularly clean sterilizing tools so they can’t inadvertently transfer insects between plants, and immediately removing any dead leaves that fall off your plants.

Water or spray your plants early in the morning or evening, and before spraying pesticides. Water can wash mites away.

Finally, it’s not a bad idea to introduce predatory mites into the mix by using organic soil. These mites prey on spider mites, and we’ll discuss them more in a moment.

Getting Rid of Spider Mites

Once you find signs of a two-spotted mite infestation, the clock is ticking. Here are some steps you can take to battle the invaders after you’ve immediately removed and carefully disposed of any affected leaves.

Ladybugs and Beneficial Mites

If you’re growing outdoors, you may be in luck; ladybugs, which eat spider mites, often sense the mites’ presence and show up on their own. For indoor grows, introduce them into your crop as soon as you know there’s a problem. They’ll stay until all of the mites are gone.

The predatory mites we’ve mentioned are a very good weapon to use. There are specific species that work well on two-spotted mites: P. persimilis are the best choice, but N. californicus and N. fallacies are also often used. You can find them in garden shops and online.


Forceful sprays of water will dislodge two-spotted mites, their eggs, and webs from cannabis leaves. Hit your plants with strong jets of water 3-4 days in a row once you’ve discovered that the mites have arrived. For added effectiveness, add vinegar or citric acid to the water (it won’t hurt your plants).

Some people also vacuum the leaves after watering, but that can be dangerous in a grow room unless you’re extremely careful not to let any fall onto the ground or into other plants. If you go this route, empty the vacuum into a freezer bag and freeze it for a few days (to kill the mites) before throwing it away.

Contact Sprays

Contact sprays are much safer than systemic treatments to use on your weed plants. They only touch the leaves and don’t enter the plant, root system, or eventually, your body. You’ll need to be sure that the leaves are doused well enough that all of the mites and eggs are covered by the spray.

There are several sprays you can try:

  • Insecticidal soap: You can find this product in garden stores; be sure it includes potassium salts of fatty acids.
  • Horticultural oil: Also available in gardening stores, this oil is made from vegetable oils, neem oil, or petroleum oils. Only apply these oils at lower temperatures.
  • Homemade solutions: There are many recipes for these sprays online; some that shouldn’t harm your plants are mixing a tablespoon of bleach with a gallon of water, combining four parts water and six parts alcohol, or a mix of nine parts water, one part Ivory dish soap and a tablespoon of cayenne pepper.

Try several of the methods simultaneously, rotate the treatments you use, and continue your mite-fighting efforts for several weeks after discovering the pests. Spider mites can be quite resistant to treatments, they develop immunity quickly, and they take quite a while to completely die off. If you have infested leaves or plants, remove them from your grow or garden so the mites can’t spread to other plants.

And if you’ve been unable to control the infestation, call in a weed-friendly expert from a pest control company. Some two-spotted spider mites colonies are simply too stubborn for a gardener to control on their own.

How to Get Rid of Spider Mites on Weed: FAQ

Q: What about using pesticides?
A: That’s a tricky one. Pesticides can easily leech into the buds and you’ll end up ingesting them. Some people use an insecticide like bifenthrin, but it’s not the best idea. Bifenthrin and similar pesticides aren’t normally harmful to humans, but a test done by Los Angeles officials on three weed samples from dispensaries found that two had extremely high levels of bifenthrin — and one contained 1,600 times the “legal digestible limit” of the pesticide.

Q: Shouldn’t clones be safe to bring into your grow room?
A: Not necessarily, and they may even pose a greater danger. Clones grow somewhere else before you get them, and they can just as easily be infested in someone else’s facility. The bigger problem is that if two-spotted spider mites are on a clone you’ve purchased or been given, there’s a good chance they’ve already survived efforts to kill them and they’ve developed immunity to most of the methods you might use. Isolate your clones, inspect them, and hit them hard if you find mites. Otherwise, you may end up having to toss them.