How to get rid of Thrips in a Marijuana Culture

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Identification, treatment and prevention

Hey there and welcome (back) to Free The Tree!
If you’ve been following our Indoor Grow Journal you aware that we’ve had issues with Thrips and that they’ve recently popped back up. Since we’re dealing with them again we figured why not to a post about killing thrips in your Indoor Marijuana Culture.

Before we get into it, if you’re looking for more information on Thrips and Spider Mites here’s a couple links to our other guides

How to Kill Thrips on Marijuana Plants

Whether you decide to use Neem oil or a pesticide the main steps of preparing your solution will be the same, here’s how to proceed:

  1. Identify the most infected leaves. You’ll see silver or white marks showing up on the leaves.
    This will spread little by little as the Thrips eat away the chlorophyll in the leaves.
  2. (optional) If you see that a section really has a large amount of Thrips and very damaged you can remove it.
  3. About 15 minutes before lights out spray your plants vigorously with your watered down pesticide or organic solution.
    Use warm water when preparing the solution.
    Don’t forget to spray under the leaves, on the stem and the soil around the stem!
  4. Follow-up: Follow up is necessary in order to take out survivors or newly hatched individuals.
    Our advice is to spray the next day, then about 2 days later with a final spay 3 to 5 days after that. If you really want to be safe you can do one last treatment couple days after that. Just bear in mind that the hatching period is of 3 to 5 days.
Microscope view of thrips larvae on the base of marijuana leaf

And voilà! You should be Thrips free! You can thank mother nature she didn’t send you spider mites, those little suckers are much harder to deal with.
Keep in mind that the damaged leaves will not recover from the damage but the spreading will stop.

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Killing Thrips organically

We’re going to cover the 3 main ways to deal with Thrips without going nuclear. The first situation, using sticky traps, is really just a control option. The 2 following techniques have proven their worth through trial and time. If you’ve tried all this, scroll straight to the bottom part of the page where we cover different pesticides used to get rid of Thrips.

Yellow Sticky Traps

Sticky traps are the first line of defense against the spreading of Thrips within a culture.
They’ll attract the adult Thrips and capture them which means that they won’t be able to lay eggs in the other plants.

This solution is definitely not a final one but it’s a good way to manage the spread of the infestation until you get can a more serious solution in place.


  • Will reduce the spread of Thrips by capturing the adult.
  • Application in simple. Once placed in the grow room there’s nothing else to do.
  • Will not kill larveas and eggs.
  • Not a final solution, just a patch to reduce spreading.

Neem Oil

Neem Oil would be our Top pick, totally organic and very effective its only downside is solubility, apart from that it’s a godsend. Its most active component, Azadirachtin, is very effective against a wide range of pests including Thips and Spider mites.

Basically what neem oil does is mess up the system of the insects. It will alter their feeding abilities as well as their hormone system, reducing their ability to lay eggs.

Neem oil is also a repellent, so on top of killing your existing Thrips it will avoid any new nuisances to come bother you.
Our advice, especially for outdoor or US growers, add Neem Oil into your regular feeding diet.

What is Neem Oil

Neem Oil, also known as Melia Azadirachta, is an oil produced with the seeds of the Neem Tree. Its oil contains many natural pesticides and is effectively one of the best natural pesticides out there for indoor growers.
It has been used for hundreds of years to control pests and diseases but is strongly lobbied against by pesticide companies.

Characteristics of neem oil

  • Yellow to brown color.
  • Can become solidish if kept under 15°C.
  • Strong garlic/sulfur smell.

Advantages & disadvantages

  • Totally organic oil.
  • Effective against a Thrips and Spider Mites, as well as many other pests.
  • Non-Harmful to frien
  • Good for dry skin.
  • Harmless to kids, pets and plants.
  • Coverage is what determines effectivity
  • Shouldn’t be used during the end of the flowering stage, it could leave a little task on the buds.
  • Don’t re-use once mixed. The oil will group together and will leave white spots (clumped need oil)  on your leaves, not cool. It’ll come off, but it’s just best not to do it.
  • Consuming too much Neem oil can make you stomach sick, make sure you don’t spray you buds, or that you wash them after harvesting

The National Pesticide Information Center has a good piece will all the details on Neem Oil if you want to check it out.

Insecticidal Soaps

Insecticidal Soaps are a good way to deal with early infestations, what it does basically is suffocate the thrips. What can be understood also by that is coverage and repeated application is very important.

What are Insecticidal Soap

Insecticidal soap, also known as Fatty acid salts, is based on Potassium Fatty Acids. These fatty acids are used for a large range of pests control, such as Thrips or Spider Mites.
Since they work on contact with the pest the plants need to be entirely soaked in the solution in order to be effective.
Insecticidal soap is can also be found under the names “potassium salts of fatty acids” or “potatssium laurate” as the active ingredient.

If you want to have a more in depth read on this soap check out the wikipedia page, it covers the subject very well.

Characteristics of Insecticidal Soap

  • Active on contact with the Thrips by weakening their outer shells.
  • Coverage is very important.
  • Don’t last long on the plant.
  • Although considered safe don’t get them on your buds!
  • Most effective when disolved in water.

Advantages and disadvantages of Insecticidal Soap

  • Doesn’t leave much residue on the plants.
  • Safe around pets and children.
  • Totally organic
  • Coverage of the full plant is necessary
  • Many repeated applications are necessary.
  • Be careful not to soak the ground too much, the fatty acids could suffocate the roots.

Our Personal Suggestion

So after couple months after fighting Thrips and recently fighting Spidermites again here’s our tip, USE COMBO’S!

The combo we’ve favored is mixing Neem oil and Black Soap.
The Black Soap allows the Neem Oil to mix into the water and also ensures the coverage of the mix onto the plants.

The black soap will improve coverage and get the thrips to suffocate; making them run into the neem oil, which in turn will soften their exterior shell and kill them.

With this you’ll increase your chance of killing them but remember, coverage is essential! If there’s a couple that survive they’ll be back. 

If you really can’t get rid of ’em, go to laddybugs! (make sure they’re lab made though)

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Killing Thrips with Predators

Thrips have many predators but you have to make sure that these guys won’t also harm your plants while getting rid of your infestation. Globally in the grower world you’ll the 2 main predators that are used are Nematodes and Lady Bugs, so that’s what we will cover:

Predators : Nematodes

With Nematodes you really have to be careful and get the right kind, some Nematodes can strongly damage you harvest so be careful!

You’re going to want to go with either the Steinernema Carpocapsae or the Heterorhabditis Heliothedis, 2 of the most know types of Predator Nematodes. Natures Control has a good fact cheat available here if you want to know more.

Nematodes will feed on the trips eggs and early stage larvae that are in the soil. They should be used in combination with a foliage treatment or predators that will pray on the adults. 

Characteristics of nematodes

  • To be stored in the fridge
  • Once placed in water they will reproduce very quickly; don’t start with too many
  • Do not confuse with Pest Nematodes
  • Extremely small – 1 Million Nematodes fit on a small 2 inch sponge.
  • Release in early morning or evening. Sunlight harms them until they’re watered into the soil.

Image credit to Natures Control

Advantages & Disadvantages of nematodes

  • Very effective and totally natural.
  • Doesn’t matter how you introduce them into the environment. You can place them in a solution and spray them or just pour the solution onto the soil.
  • Must be applied within the 2 hours after placing in water, or else they start to drown.
  • Treatment can take a while (4 to 6 weeks depending on the infestation).
  • Can only be stored up to 2 months.
    If you see them drying out within that time period, place a couple drops of water.
  • If the soil doesn’t stay moist the Nematodes will die.
  • Quite expensive (~18.00 USD’s for One Million Nematode sponge)

Image credit to Natures Control

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Nematodes killing Fungus gnat larvae

Predators : Lady Bug larvae

I find that Lady Bug larva’s are the most elegant way to get rid of Thrips. Something about lady buds I’ve always enjoyed, so giving them something to thrive is pretty cool.

Generally it’s much easier to go ahead and buy some larva’s, let them grow within your room. While developing they’ll go ahead and start feasting on those nasty little Thrips.

Close up on larvae on a leaf

Advantages and Disadvantages of lady bugs

  • Easy to purchase.
  • It’s organic and natural.
  • “Hands-off” solution. You just have to make sure that they don’t all die.
  • Nature’s answer to Thrips.
  • If well introduced, you have protection “for life”
  • You could find some dead lady bugs in the buds during the flowering stage.
    If it’s a personal grow this isn’t really a problem, but if you’re looking at selling it to a dispensary it may not be the best choice.
  • If your room isn’t well sealed they could exit the room.
  • Some producers are very unethical, “harvesting” the lady bugs when they go up to the mountains to rest for the winter time.
    Make sure to check out how your retailer gets his lady bugs.
Ladybug larvae hunting aphid

For that last reason we actually discourage the use of Lady Bugs. Except if you can really make sure that the lady bugs have not been caught in the wild in order to get larvae’s out of them, it’s really counter-intuitive to get them thinking it’s a “good for the nature” move.

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Using Pesticides to get rid of Thrips

So you there are a wide range a pesticides that are effective against Thrips invading your plants. Here we’ll cover the most well known and proven one’s, it should be definitely be enough for you guys to deal with your infestation.

We definitely recommend that you try out the fully organically methods before switching to pesticides.

Here’s what we’re going to cover:

Spinosad Concentrated Products

You can find a wide range of brands on the market that are based off Spinosad.
Here’s a little context on this pesticide on this pesticide, how it kills thrips, its advantages and disadvantages:

What is Spinosad

Spinosad is a product derived from the fermentation of lowly soil bacterium juice called Saccharopolyspora spinosa. To chemists, spinosad is a complex molecule known as a “glycosylated macrolactone;”.
For us gardeners looking for safer and organic products, it may be a godsend. This product has been around for awhile now, it was granted the Organic Status by the USDA’s National Organic Program back in 2003.

Although it’s been around for that long many gardners aren’t aware of its effectiveness against Thrips and Caterpillars.
Unlike many other insecticides, you can spay it directly and heavily on leaves and roots with no, or almost no, negative effects.

Saccharopolyspora Spinosa will kill Thrips via ingestion or contact by effecting their nervous system.

Bottle of concentrated spinosad product

Advantages and disadvantages of Spinosad

  • Fully organic.
  • Harmless to pets, children and other plants.
  • Harmless to non-threatening insects.
  • Very effective against Thrips and Caterpillars.
  • Can be used as a preventing agent and a killing agent.
  • Very effective for outdoor growers, killing Thrips but not harmful to other beneficial insects
  • Most products are effective about 24 hours after creating the mix – Only make what you need.
    All extra mix will be wasted..
Spray bottle of spinosad insecticide


You can find a wide range of brands that are based off Spinosad. Here’s a little context on this pesticide:

What are Pyrethrins

Pyrethrins are the active chemicals present in the Pyrethrum Daisy.
Derived from this plant, these chemicals are not very toxic for humans and degrade quickly but insecticides nonetheless.

Generally recommended for vegetable gardens, personally I think there are many other ways to combat your leaf-hopping pests than pyrethrins.

Characteristics of pyrethrins

  • Break down quickly, about a day or two is necessary.
  • Active Chemicals extracted from the Pyrethrum Daisy.
  • Needs to be sprayed evenly across the plant using a mister (aka One-Hand Pressure Sprayers).

Advantages and disadvantages of pyrethrins

  • Very effective.
  • Quick break down cycle, meaning that it will not stay in your soil/plants for long.
  • As pesticides go, considered as a less harmful one.
  • Certified organic by the USD
  • Very harmful to bees. You will need to apply this after sun down when the bees are asleep so that it will have started to break up when they wake up.
  • If Indoors be careful of the fumes, don’t let them get too concentrated in the room

Best way to get rid of Thrips

Our personal favorite is definitely the combo Neem Oil & Insecticidal soap.

It works very well against Thrips or Spider Mites in case you’re not sure which one you have and it’s totally organic. If you find a eco-responsible grower there’s basically no bad effect to our mother earth.

The main issue with neem oil is solubility, and in the end it’s not that big of a deal since it’s very potent.

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Well that it for this one folks!
Until next time, be safe and grow easy

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