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thrips on marijuana

Thrips – How To Get Rid of Them?

Thrips are a common threat to cannabis cultivators. They are small pests that look like little worms or flying insects. They are tough to get rid of and survive by sucking the sap out of your plants. Here is a quick guide to spotting thrips, and a few ideas for preventing and controlling an infestation.

Growing cannabis can be an exciting and rewarding hobbie. But what happens if others decide to enjoy your cherished crop before you do?

WHAT ARE THRIPS?

Thrips are a common problem faced by canna-cultivators. They are a minute pest that literally suck the plant sap out of your crop. Thrips also come in several different species. They can be tiny winged insects (measuring in the millimetres), or they can look like small, pale worms.

Regardless of their species, thrips are the bane of farmers everywhere. They can reproduce up to 12 times per year. When mature, they can survive just by flying from one plant to another. Outside of cannabis, thrips’ favourite crop seems to be cotton, although they can damage many kinds of crops. But they really seem to love cannabis! Unfortunately, they are particularly damaging when they appear early on in the grow process.

The most damaging thrip threat to cannabis comes from a species called Frankliniella occidentalis. These thrips are yellowish-white flying bugs. They lay their eggs on the plant itself. The first signs of their presence are small, silver stains or dots on the underside of leaves. This is how thrips lay their eggs. They are also easy to miss.

Worse? While not a significant threat to outdoor growers, they thrive inside. Indoor grows and greenhouses are their favourite environments. They love high temperatures. Thrips can also be persistent if not treated properly. And if not eliminated early, they can significantly reduce yields.

THRIP PREVENTION AND CONTROL

The best way to rid yourself of thrips is to never have an infestation in the first place. Make sure that you thoroughly sanitise your growing space before you begin. This means not only keeping the place spotless, but removing all dead plant matter.

Once the grow space is set up, install insect adhesive strips. Much like fly paper, these are insect traps that will catch most of the free-flying bugs around. The bugs will get glued to the strips. Problem solved.

Eradicating thrips once they have established a presence is the only way to save your crops and prevent a new infestation. The best method (without using harsh chemicals) is to use potassium soap or neem oil. Pyrethrins and rotenone are also good options, although use sparingly as pyrethrins are also highly toxic to bees.

Neem oil serves as a completely natural way to protect your cannabis plants against pests.

Neem oil serves as a completely natural way to protect your cannabis plants against pests.

Spinosad products are also organic and harmless to pets, children, and plants. Spinosad is an organic pesticide made from the fermentation of certain kinds of soil bacteria. This form of insecticide can be used both as a topical spray and at the roots. When added to water, these products are only good for about 24 hours, so only mix what you need at any given time.

If you want to use chemicals to clean your space and crop, try to use the least toxic substances available. Remember to use both masks and gloves when handling all toxic chemicals.

Introducing natural predators like Orius laevigatus (the common bed bug) is another way to keep your harvest thrip-free.

Thrips are a common pest facing indoor cannabis cultivators. They can seriously damage the plant and lower yields. Here is a guide on how to get rid of them.

Thrips

What Does Cannabis Thrip Damage Look Like?

Adult thrips are small, fast-moving insects, while young thrips look like tiny unmoving pale worms on the leaves. In fact, thrips can come in many forms, from wormy nymphs to dark or golden winged insects, depending on the stage of life and where you live.

They pierce cannabis leaves with their mouths and suck out all the good stuff, leaving shiny (sometimes people think it looks slimy), silver or bronze spots wherever the leaves were bitten. The spots are bigger and more irregularly shaped than the bites left from spider mites. If it goes on too long the affected leaves may start dying.

Examples of thrips damage on marijuana leaves (irregular silver or bronze spots)

Although it doesn’t really look like it in pictures, in real life thrip damage has been described as looking like “dried spit” or tiny snail trails.

(thrip leaf damage pics by theMallacht)

Here’s a picture of an adult thrip on a finger for scale – they’re tiny!

They can appear dark colored like the ones above, but also yellow, transparent or golden

They can appear with or without wings, depending on their stage of life

In their “nymph” (juvenile) form, thrips appear pale, fat and almost wormy from afar

A closeup of another baby thrip in “nymph” form

A Thrip nymph on a cannabis leaf – I hope this helps show you how tiny they are.

A thrip nymph looks tubular and worm-like, unlike an aphid nymph which looks like a tiny white bug

Proven Thrip Remedies

1.) Insecticidal soap

Fatty acid salts or insecticidal soaps can be a good choice against thrips. They weaken the outer shell of thrips but are safe to use on your plants and they don’t leave much of a residue.

With soaps, coverage is very important as it does not stay on your plant for long, so follow-up applications may be necessary. Although this is considered safe, avoid getting any on your buds!

2.) Neem Oil

Neem Oil will leave an unpleasant taste/smell on buds when used to treat flowering plants, so don’t let this stuff get near your buds! There’s also some evidence Neem oil may be harmful to humans so use with care! That being said, Neem oil is an all-natural remedy that is very effective against many different types of bugs and mold. You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly since neem oil and water can separate easily.

3.) Spinosad Products

Spinosad products are organic and unlike many other thrip pesticides, completely harmless to pets, children, and plants. Unlike many insecticides, you can spray spinosad heavily on leaves and roots with basically no negative effects. Spinosad products can be used directly to kill thrips on contact, but can also be used when watering plants to systematically kill thrips via the roots. Spinosad is also effective at fighting caterpillers, spider mites, and many other marijuana pests.

Can be used both as a topical spray, and can also be used directly at the roots. Spinosad is an organic insecticide made from the fermentation of a specific soil bacteria (actinomycete Saccharopolyspora spinosa) and kills thrips via ingestion or contact by affecting the insect nervous system. Spinosad can be a good choice for organic and outdoor growers, because it is very toxic to thrips, but is less toxic to many beneficial insects.

Note: Most spinosad products are effective for only about 24 hours after being mixed with water, so only mix as much as you will need per application. Anything left over will be waste.

4.) Pyrethrins

Pyrethrin based insecticides are not very toxic for humans and degrade quickly, which is why they’re commonly recommended for vegetable gardens. You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly.

Pyrethrin products break down quickly, over the course of just a day or two. The major problem with them is they are very toxic to bees. Although cannabis plants generally don’t attract a lot of bees, please use this as a last resort, and also try to use it right after the sun goes down because bees sleep at night. This lets it start to break down before they wake up.

Use pyrethrin products when the sun goes down! Save the bees!

A popular example is Bonide 857 Pyrethrin Spray Concentrate. Use 3 tablespoons of concentrate per gallon of water.

Plant Symptoms

  • Bronze or brown patches
  • Brown or slimy roots
  • Brown or yellow leaf tips/edges
  • Buds dying
  • Buds look odd
  • Bugs are visible
  • Curling or clawing leaves
  • Dark leaves
  • Drooping plant
  • Holes in leaves
  • Mold or powder
  • Pink or purple on leaves
  • Red stems
  • Shiny or smooth leaves
  • Spots or markings
  • Twisted growth
  • Webbing
  • Wilting leaves
  • Yellow between leaf veins
  • Yellow leaves

This page is part of our Plant Doctor series. You can use our tool to filter by symptom and help diagnose your plant.

If you see tiny, wormy little bugs, dark winged insects or bronzed discoloration on the leaves, you may have thrips. Learn how to get rid of them!