Spider mites on weed plants

Of all the possible invaders getting into your marijuana crop, spider mites on weed are by far the worst.

They’re a common cannabis pest and can be hard to get rid of.

Spider mites are not actually insects, but rather arachnids (like spiders) since they have eight legs and lack antennae.

They also have an oval-shaped body and are related to ticks and other mites.

They are called spider mites because of the web that they spin on your plants’ leaves and flowers.

What are spider mites

Spider mites are so devastating to weed plants simply because of their extremely high reproductive rate. Eggs hatch in just three short days, and five days after that the spider mites have reached sexual maturity. At this point, they will begin reproducing rapidly. A female spider mite could lay millions of eggs in one month. Do you see the issue here?

Spider mites on marijuana plants

Spider mites like your weed plants because they eat chlorophyll, the substance all plants need to achieve photosynthesis.

They have little teeth that bite into one plant cell and remove the chlorophyll. Imagine that happening from millions of spider mites at one time – this is how entire crops are destroyed.

Spider mites can appear in any setup, but they are less common in hydroponic growing systems.

They are especially common in soil because there is more dead organic matter.

Spider mites can destroy your weed plants at an incredibly rapid speed. Bad infestations have been known to actually kill a plant overnight.

They also are extremely adaptable, and they grow immune to your method of killing them. This happens if your method hasn’t worked completely, and some spider mites were left.

Then you will soon end up with an army of super spider mites that are immune to whatever method you tried using.

Two-spotted spider mites are especially resilient to insecticides. They specialize in eating weed and are often called “the Borg” by marijuana growers.

The spider mite life cycle is what makes them so resilient as a species. When adult females lay their eggs, they will hatch within a few days (or sometimes weeks).

The hatched organisms are called larvae, and they have round bodies with three sets of legs instead of four.

These larvae will feed on your plant for several days until they choose a spot that is protected or sheltered and then molt, thus entering their first nymphal stage.

This first nymph has four sets of legs instead of three.

A first nymph follows a similar pattern: it eats for several days, then finds somewhere to rest and mold into the next phase – the second nymph.

The second nymph follows the same pattern. It eats for a few days, rests, then molts into the final adult stage. They have thus reached sexual maturity.

Male adults remain roughly the same size as a second nymph, and their abdomens are pointy. Females’ abdomens are round, and they are larger than males.

Due to this unique life cycle, if you kill off all the adult spider mites then you might think you have eradicated the problem altogether.

Unbeknownst to you, the less mature spider mites could still be happily chomping away at your plants, about to enter their own adult stages of life.

Signs of spider mites on weed

Spider mites on weed can be tough to notice right away, making it difficult to get ahead of the game when it comes to eradication.

They will appear like little dots to the naked eye, no bigger than the tip of your pencil lead.

Many growers don’t notice that there is anything off until the infestation is big enough that it’s impossible not to see.

Marijuana spider mites leaves

This is why it’s extremely important for you to do routine leaf inspections. Check both sides of the leaves to see any spider mite damage.

Do this often, because you will need to have enough time to act faster than the speedy spider mites.

Spider mites generally live on the undersides of your weed plants’ leaves. Much like a “normal” spider, spider mites spin a web to keep their eggs and colony safe.

You should be able to notice when a spider mite is making its home beneath a leaf because you will see fine white strings between leaves.

If you do, you will know there’s a problem to be dealt with. You also might see the fine silk on your plants’ foliage.

This sticky silk will collect dust and dirt and will make your plant look dirty. It is especially common in a flowering room to see buds covered in this fine webbing.

The first signs of a spider mite problem will be seen on the leaves. Tiny specks will begin appearing – these specks are actually little bite marks from where the mites took a chomp of your plant.

These spots might be yellow or white in color.

If a weed plant is badly infested with spider mites, the whole thing will start looking sickly and discolored, and could eventually just die.

Not sure if spider mites are causing the damage to your marijuana plants? Check the article Marijuana pest and bug control for a list with pictures of all pests and bugs

Download my free marijuana grow guide for more growing tips.

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    Prevention of spider mites on weed

    There are several ways you can prevent a major infestation of spider mites on your weed plants.

    If you use an organic compost mulch, for instance, you will be unknowingly adding predatory mites to your plants’ defenses. These beneficial mites eat the spider mites.

    spider mites on cannabis plants

    Never bring in plants from the outside

    Other tips for prevention include never bringing in plants from the outside into your grow room.

    This is the most common cause of a spider mite infestation. If you have an external clone or a weed plant from elsewhere, keep it under quarantine for a minimum of two weeks.

    You can even check it with a handheld microscope.

    Don’t let anything wander around in your grow area that shouldn’t be there

    You also shouldn’t allow old, dead leaves to sit in your marijuana grow room – ever.

    Pick up any dead leaves on a regular basis and put them in a totally new location. Just make sure you move them out of the grow room!

    Cleanliness is also key – don’t ever walk into your grow room straight from the outside; ensure your cleanliness first.

    Don’t let any pets into the grow room, and keep the airflow nice and consistent.

    If you have air coming in from outside, apply a filter of some kind to keep bugs out.

    It’s best to start your crop out with seeds instead of clones, especially if you are only growing for personal use. Keep temperatures on the lower side, since spider mites love the heat.

    How to get rid of a full-blown spider mite infestation on your weed plants

    Firstly, ladybugs eat spider mites, although if you purchase them they will fly away as soon as their source of food is gone, so they don’t work as well preventatively.

    They often show up to your crop naturally when you have a spider mite problem, in which case you don’t need to buy any ladybugs. Mother Nature can be awfully helpful sometimes.

    If you were unable to prevent an infestation from occurring, there are a few steps you can take to handle the problem before it destroys all of your plants.

    Using a hard water spray to get rid of spider mites on weed

    First, use a hard water spray to hit your weed plants, three mornings in a row.

    The water pressure alone should take care of the bugs and their webs. They will fall to the ground and, unable to move anywhere else, will eventually die from lack of food.

    A commercial product like Bug Blaster will always to the job. If you want to make sure to kill them all buy something like Bug Blaster.

    Using a vacuum cleaner to get rid of spider mites on weed

    Another option is also deceptively simple. Try using a handheld vacuum cleaner to simply suck the mites straight off of your leaves.

    This takes a bit more time but should be an effective way of removing the mites. You should then carefully put the contents of the vacuum into a sealable plastic bag, then put that bag into the freezer.

    The mites will die from the cold since they live in higher temperatures. Then simply get rid of the bag with the rest of your trash on garbage day.

    Never simply assume it’s all over…

    One potential problem you could run into is an apparent resurrection of the spider mites. This is every marijuana grower’s worst nightmare.

    Of course, it is not actually the same spider mites coming back to life.

    It is actually their millions of eggs that all hatched within a few days or weeks of when you thought you had gotten rid of these pests.

    If you bought ladybugs to take care of the problem, this could occur after they have already flown away in search of more food.

    You will have to use a different method or buy a new set of ladybugs – but you better do it quickly!

    You can also go to your local gardening center and see what sprays they have to get rid of the mites.

    An additional option is to use neem oil. You should shake your plant and then kill them with neem oil or another product that will kill the spider mites on contact.

    Be careful with the neem oil, however, as it can harm humans.

    Other options to get rid of spider mites on weed

    Some other options are using a bleach solution made of 1 tablespoon of bleach to 1 gallon of water that is 95 degrees Fahrenheit and pH balanced), or alcohol and water (30% or more of the solution should be water to avoid hurting the weed plant itself).

    You could also make a homemade pepper spray (9 parts water, 1 part dishwashing soap that doesn’t have any additives, 1 tablespoon of cayenne pepper), nicotine tea (15 grams of organic tobacco, steep with hot water overnight), dichotomous earth (fossil dust that can be sprinkled over your weed plants), or insecticide.

    Only use insecticide for extreme cases, and do it by treating your entire grow room with broad-spectrum insecticide.

    Spider mites on cannabis plants

    Please note: Anything that contains Abamectin or Lindane is harmful to humans. Make sure you know what is in your treatment and proceed with caution.

    After two or three days of using one method, follow up with another method as well as re-using the original method. Repeat the entire process one more times – or more!

    Once you think you’ve taken care of the spider mite problem, treat the area a minimum of one more time.

    Because spider mites like to stick around on weed and resurrect their numbers after you have treated your crop already, make sure that you continue treating after the infestation appears to be gone.

    Always assume they are hiding away, preparing secretly to destroy your plants as soon as you turn your back. Kill them before they can.

    Use multiple methods when you are exterminating the spider mites so that you can ensure they all die. Constant, varied attacks are the best way of handling this mighty foe.

    Spider mite on weed – plant symptoms

    Leaf symptoms:

    • Brown, dark spots
    • Mottling or mosaic pattern
    • Slowed growth
    • Webbing on leaves

    Plant symptoms:

    • Slowed growth
    • Wilting or drooping of plant
    • Bugs
    • Buds not fattening

    If you’re growing indoors, it’s important to determine where exactly your spider mites came from. This is a good thing to do before you start using everything in your power to destroy them.

    Are you experiencing more symptoms not listed above? Check out our full list of marijuana disease symptoms!

    Were the spider mites just randomly brought into your grow room from the outside?

    They could have come from a vegetable garden, from animals or your pets, or from another plant that isn’t marijuana.

    If they were just tracked in from outside, they most likely they are your standard non-super spider mites, so you can go ahead and use a simpler home remedy to take care of them.

    If, however, they came from another marijuana grower, you may have a tougher time killing them.

    If they came from clones you used or maybe were somehow tracked in from someone else’s marijuana garden or any other situation where the spider mite was living on someone else’s weed plants, then this is not a run-of-the-mill spider mite.

    Instead, this is a marijuana expert. If they are two-spotted spider mites, you will have a very difficult time with them. They are probably already immune to lots of eradication methods.

    You should, therefore, use the strongest remedies immediately. Don’t wait around and play games, or your entire crop could easily get destroyed.

    Remember that weed plants with strong genetics have less chance of getting sick and are less vulnerable to pests and diseases. So make sure to buy cannabis seeds from a trusted seed bank.

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    FAQ about spider mites on weed

    What causes spider mites?

    The most common cause of spider mites is bringing plants from the outside into your grow room. You’ll also encourage a spider mite infestation if you let pets wander around, let dead leaves sit in your grow room, and expose your plants to high temperatures.

    Do spider mites ruin weed?

    Yes, they do. Spider mites eat chlorophyll, so plants can’t achieve photosynthesis. Worst of all, they have a high reproductive rate, making it possible for them to destroy many crops in a short time.

    Can I use neem oil for spider mites on weed?

    Yes, you can. Make sure you shake the plant before using the neem oil. Remember to exercise caution since neem oil is harmful to humans.

    Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible


    Avatar for Robert Bergman

    Robert Bergman

    Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations. His passion for growing led him to develop his own Gold Leaf strain. Now, Robert is dedicated to sharing his knowledge with the world.... [Read full bio]


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