How to get rid of Thrips in cannabis plants

What are Thrips?

Thrips are one of the most common pests in cannabis crops, especially in indoor growing spaces and greenhouses. These are one of the smallest winged insects, measuring 1.2mm (females) and 0.9mm (males) when adults. Eggs measure around 200 microns and are withish in colour, being layed in the plant tissues. Normally, thrips are found on the underside of the leaves.

There are many varieties of Thrips, being the Frankliniella Occidentalis - also known as western flower thrips - the most commonly found in cannabis plants.

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Thrips attack a large number of plants (Photo: Jean and Fred)

The western flowers thrip is originary from California and was introduced in La Península (Almería) in 1986 from Holland, causing considerable damage to cotton crops. Today, it is one of the most common pests worlwide, since it can damage a large number of plant species.

Thrips in indoor cannabis crops

While not being extremely agressive with plants, thrip pests are common in indoor growing tents or rooms. As happens with red spider mites, thrips need high temperatures to appear and can be persistent if not treated properly. The first signs are small silver dots/stains on the surface of the leaves, which are the places were thrips have bit or layed their eggs.

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Cannabis leaf with symptoms of thrip infestation

As we mentioned, thrip pests don't usually kill cannabis plants, but if the pest is not treated it can significally reduce yields and affect the overall health status of the plant. As the pest progresses, we can notice very small black dots on the leaves, which are thrip feces.

Thrips in outdoor cannabis crops

Thrips do not represent a serious threat to outdoor cannabis plants. We can find few leaves with some thrips on their underside, especially at the beginning of summer, although they usually don't compromise our harvest.

Prevention and control of thrips

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Potassium soap helps to prevent and erradicate thrips

As usual, we recommend you to have your growing space and its surroundings clean and free from dead plant material, etc. Using blue adhesive strips for thrips allows us to kill most adults, being also usefull to check if we actually have thrips in our crop, since they'll get "glued" to these strips.

Using potassium soap or natural pyrethrins regularly will help us to prevent the appearance of thrips, also to erradicate them if we don't want to use chemicals. Expelex works great for this pupose.

We can also use natural predators such as Ambliselius cucumeris or Ambliselius degenerans, also the bedbug called Orius laeviatae.

As last option, and always taking caution and carefully reading the instructions, we can use chemical products to erradicate thrips. Confidor from Bayer is extremely effective. Always remember to protect your environment from toxic substances and to use protective gloves and facemask when handling them.


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Comments in “How to get rid of Thrips in cannabis plants” (7)

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Zinger59 2020-11-06
Neem oil every 7-10 days during vegetation and/or potassium salts will control thrips. Adult thrips have wings but prefer to run and jump. You have to keep ahead by a rigorous spraying schedule. Spray both top and underside of leaves with lights off.

alchimiaGrow 2020-11-09

Hi, that's great advice, thanks for your contribution. Best wishes and happy growing!

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Bob - O 2020-07-27
I seem to always have Thrips I kill them every grow only to have them back next grow... I've sprayed Mercenary by Cultured Biologicx n I've used Biologic Army by Pure Ag what more can I do

Tim Alchimia 2020-07-28
Hi Bob, thanks for the question. Sorry to hear about your troubles with thrips, they are persistent little critters, that's for sure! I'm seeing more and more people talking about using nematodes to control thrips. Apparently, when applied to the soil they hunt the thrip larvae and eat them, proving to be very effective at controlling the pest problem. I'd wager that nematodes, in combination with the spray measures you've already taken, will help a great deal with this problem. Best of luck and happy growing!

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Edward Thompson 2019-10-09
Nematodes eliminates my thrips. U will use them automatically now every year.

Tim Alchimia 2019-10-14
Hi Edward, thanks for your input, that sounds like a very interesting treatment, would you mind telling us more about how the nematodes are applied to the plants, please? All the best and happy growing!

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steve walton 2019-09-07
It may have thrips. Cut one of the buds open and see if there are any insects crawling around inside the bud. IF you have thrips you will need to treat it with an insecticide specifically for thrips.

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Carol 2019-02-17
THRIPS well they our a four letter word, they just spelled it wrong..I was and still am pissed..We are building our room around the plants. Was not the plan, found a seed and 14 plants later...I thought I had a cal-mag problem and before I knew it I had an infestation. Tomorrow i will be shutting the light off and spraying with The Amazing DoctorZymes Eliminator..Organic spray. It is for everything..Next round of plants I will be giving them Organic Neem oil every ten days during veg..I will be doing my boogie brew teas until I can start making my own..I'm older, 62 and first grow, my heart sunk when I spotted a bug.. I would like to know if anyone out there has had any luck with Doctor Zymes Spray? Any kind of support of advice would really be appreciated.

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moe 2016-08-19
I have recently found thrips on the top of my leaves and sprayed them with a heavy fire of ciggeratte butt juice . 32 oz bottle 14 plants that are not huge but are not small by any means .

Dani Alchimia 2016-08-22
Hi moe, Due to its antiherbivore action, nicotine has been widely used in the past as insecticide. Still, keep in mind that nicotine is not approved as pesticide for organic farming (US Code of Federal Regulations). Thanks for your comment!

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Lyndon Palmer 2015-12-22
How well does Dawn dish soap work .And then if so how often

Dani Alchimia 2015-12-22
Hi Lyndon, From what I read, Dawn is a Triclosan-based soap, which can be hazardous for humans. I'd rather use potassium soap, it is much safer and easy to buy. You can use it once a week with no problems, even if you don't see pests. I never recommend spraying the plants during flowering. Best vibes!

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