How to Deal With Thrips On Cannabis Plants?

Thrips are notorious creatures that many cannabis growers find lounging on their plants every year. And while these small insects may look harmless due to their worm-like appearance and small stature, they can do a lot of damage to your cannabis plant in no time, especially if you don’t address the problem right away.

In this article, know everything you need to know about thrips as a cannabis grower and the steps you need to take to deal with them effectively. 

What are Thrips?

Thrips are one of the most common types of pests that a cannabis grower should be wary of. These tiny insects feed on the plant’s sap, which can lead to various problems for your plant. Over time thrips can significantly hamper your plant’s growth and damage its yield potential. 

You will find many species of thrips on cannabis plants, but most of them look quite similar — they are small, winged, and look like pale worms. But don’t let the size fool you — these tiny insects can reproduce up to 12 times each year. The most damaging species of the thrip family of insects is Frankliniella occidentalis, which is slightly yellowish in color.

These pests lay their eggs on the plant, which appear like silver stains under the leaves. Plus, they thrive in a humid, warm environment, which is why they are commonly found in indoor cannabis grow rooms.

How Harmful Are Thrips to Cannabis Plants?

Thrips are a significant threat to cannabis plants as they can do a lot of damage in a short period of time. Some of the biggest symptoms of thrip damage in the cannabis plant include the following:

• Distorted growth of new leaves and buds 
• Spots developing on the leaves 
• Yellow speckles on the leaves 
• Older fan leaves develop silvery patches 
• White or silvery patches all over the plant 
• Slow growth, especially during the vegetative stage 
• Discolored buds and leaves 
• Wilting of the leaves 

These damages are a result of thrips sucking the sap out of your plant, which robs your cannabis plant of the necessary nutrients. But that’s not all, thrips also open the doors for many other fungi and bacterial infections. 

Thrips lay their eggs within the small layers of the leaf tissue, and when they hatch, they create a gaping hole in the leaf’s surface, which is prone to bacteria and fungi. These bacteria and fungi can create more problems for your plant, leading to various infections, stunted growth, lowered yield, and even death. 

How to Spot a Thrip Infestation on Cannabis Plants?

You must spot thrip infection on your cannabis plant as soon as possible before it’s too late. Catching the signs early will help you fix the infestation easily — the longer you wait, the worse it gets. 

So, the first step is to start looking for thrips on the leaves of your cannabis plant. Thrips create small silvery trails on the leaves along with black marks (feces). The leaves may also grow to be deformed or brittle. 

If you look closely enough, you will also find them wandering around on the leaves, but they will often try to camouflage themselves on the veins of the leaves if they spot movement around them. 

One of the best ways to confirm if thrips are present on your cannabis plant is to use sticky traps, which will attract a few of them and trap them. Once the trap has caught some specimens, examine them to see if they are thrips or otherwise. 

Signs of Thrips on Cannabis Plants

Let’s look into how you can spot signs of thrips on your cannabis plants:

1. Silver or bronze speckles: Thrips have a needle-like mouthpart that they make use of to puncture the plant cells and draw the sap out. As they feed, they get rid of chlorophyll from the cells, causing tiny, silver, or bronze-colored speckles on the leaves. These speckles are usually a lot more visible on darker green leaves. Also, while the thrips feed, they get rid of a layer of cells from the surface of the leaves, leading to a glossy or silvery appearance. Typically, this happens because the upper epidermis containing the cuticle giving the leaves their healthy appearance is damaged. The lower epidermis that is now exposed reflects light in a different manner, thereby giving a silvery look. 

2. Deformed leaves: Thrips damages can make leaves look like they are twisted or distorted. As the thrips feed, they disrupt the normal development of the leaves, leading to leaves looking irregular and uneven. If the infestation is severe, the leaves might also reveal indications of dead tissues or necrosis on the tips. 

3. Stunted growth: Thrips mostly prey on young leaves and buds and in areas where the growth is concentrated. Since thrips attack tender parts, the overall development of the plant is interrupted, leading to stunted growth. 

4. Scabbing: Thrips can also cause scabbing on leaves that appear as scars on leaves as they feed. These scars make the plant look damaged along with a rough appearance. If you don’t address this issue, it will affect the ability of the leaves to carry out essential functions like photosynthesis, making the plant weaker. 

5. Sticky residue: Thrips secrete a sweet material called honeydew while feeding on plant sap. This sticky deposit can build up on the leaves, stems, and other surfaces of the plants. This honeydew can gradually promote the development of black sooty mold and mildew. The existence of black sooty mold and mildew is an indirect indication of a thrip problem.

How to Get Rid of Thrips on Cannabis Plants?

Thrips are not to be taken lightly — these tiny insects can do a lot of damage to your cannabis plant. So, it is best that you act early if you spot them on your plant. Remember, thrips love moisture so you must prevent overwatering the plants. Always ensure the soil at the top is dry before watering the plants further. 

First, isolate the affected plants from the rest of the plants in the garden to prevent the spread. Next, place your infected plant in another spot, away from any other plants. 

Next, prune any leaves that are affected. Snip away everything that’s likely to even have eggs. This includes even buds if they are infected already. This will prevent you from tossing the entire plant later. Next, dispose of the infected material carefully so the thrips don’t have an opportunity to spread further. 

But how can you get rid of them when they are so tiny? Here are some of the best ways to get rid of thrips on cannabis. 

1. Bacillus Thuringiensis

Using Bacillus thuringiensis (Bt) to control thrips can be an effective and environmentally friendly approach. Bt is a naturally occurring bacteria found in soil that produces proteins toxic to certain pests, including thrips. It produces crystalline proteins or toxins that are fatal to pests but are harmless to humans, animals, and beneficial insects. When the pests ingest these toxins, it binds to certain receptors in their gut that damage them internally. Eventually, the pests die, thereby making Bt an effective and easy method to get rid of thrips. 

Firstly, note that you must select the right Bt strain. There are various Bt strains and each of them targets specific types of pests. For thrips, Bacillus thuringiensis var. israelensis (Bti) or Bacillus thuringiensis var. thuringiensis (Btt) will work. You can find Bt products in liquid concentrate or powder form, available from garden centers or online suppliers. These strains produce toxins that target thrips at various stages of their life cycle.

Here’s how you use can Bt to get rid of thrips on your cannabis plants:

• Choose the Right Bt Product and carefully follow the instructions provided by the manufacturer, including the dilution ratios and application rates. 
• Dilute the product according to the instructions. Next, mix the specified amount of concentrate with water in a clean sprayer. 
• Before applying the Bt solution to all your plants, conduct a test spray on a small portion of the foliage to check for any adverse reactions. Once you’re certain there are no negative reactions, you can proceed to spray the plants. Start with the undersides of the leaves, and target other areas where thrips can hide. Make sure you spray the whole plant avoiding the buds if there are any.
• Thrips are more active during the evening and early morning, so it's best to apply Bt during these times when thrips are actively feeding. Reapply the Bt solution as recommended, typically every 5-7 days or as needed based on continued thrip activity.
• Lastly, monitor your cannabis plants for signs of thrip activity. If thrips persist or the infestation worsens, you can combine Bt treatments with other control methods for the best results.

2. Neem Oil

Neem oil is one of the best ways to get rid of not only thrips but an array of pests on cannabis plants. This oil effectively kills pests on contact and its nasty smell also prevents them from coming back to your plant. Just don’t spray it on the buds as it can significantly hamper the smell and taste of the buds. 

To use neem oil, you can dilute a teaspoon of neem oil in a liter of water (or in a similar ratio), and use a hand pressure sprayer to douse your cannabis plant with it. 

3. Diatomaceous Earth

Diatomaceous earth is fossil dust that is super effective at killing pests like thrips. While this may seem like talcum powder to us, the dust is extremely sharp at a microscopic level. This punctures the insects’ shells on contact and dehydrates them. 

So, if you want to get rid of thrips with diatomaceous earth, sprinkle some of this deadly power (for them, not us) on the soil and let it do its magic on the insects. 

4. Pyrethrins

Pyrethrin is a type of insecticide that is often recommended for vegetable gardens since it is not toxic for humans and degrades quickly over the course of a day or two. This insecticide is cheap to procure from gardening stores and you simply need to use a mister to spray your plant down with them.

However, we only recommend using pyrethrin as a last resort since it is toxic for bees. Yes, cannabis does not really attract a lot of bees, but it is still best to avoid using this if you have any bees lingering around your garden. Also, when you do use it, only use it after sunset when bees are inactive. 

5. Spinosad

Spinosad is an organic pesticide that’s completely harmless to humans, plants, and pets, but it can kill thrips and many other insects on contact. You can use spinosad as foliar spray or soil amendment. This organic insecticide is made from bacterial fermentations and, when ingested by insects, it attacks their nervous system and kills them. 

Follow the manufacturer’s recommendation on diluting and using them. And do note that most spinosad products will only be effective for a day after being mixed, so prepare the solution as per your requirement and use it quickly. 

6. Insecticidal Soap

Insecticidal soaps are rich in fatty acid salts, which are quite effective at killing pests like thrips. This insecticide for thrips weakens the outer shell of the insect and dehydrates them. But the biggest benefit of insecticidal soap is that it is completely harmless to the cannabis plant and does not leave behind any residue. 

Follow the manufacturer's recommendation on insecticidal soap and remember to get full coverage of your plant. Otherwise, you may miss some thrips here and there and the problem will persist. 

7. Orius laevigatus

You can also employ predatory insects to prey on thrips, like Orious laevigatus, which are the best predators for thrips. Introduce a batch of this insect on your cannabis plant and they will find and kill every last thrip on the plant in a few days. 

8. Sticky Fly Traps 

If the problem isn’t so severe, you can also use sticky fly traps to catch thrips on your cannabis plants. Here, we recommend using blue traps since they are most effective at trapping thrips. Once the traps are saturated with thrips, discard them and replace them with new ones. 

How to Prevent Thrips on Cannabis Plants?

What’s better than getting rid of thrips? Preventing them in the first place. So, you should do everything in your power to prevent them from ever making their way onto your cannabis plants. 

One of the first things you must do is keep your growing space clean and free of debris and weed plants. Such things attract thrips, especially during the summer months. You should also keep an eye on the temperature and humidity of your grow room since thrips are attracted to warm, humid places where they start breeding rapidly. 

Some species of thrips lay eggs in the soil, so it is recommended that you replace the growing medium between each crop cycle to get rid of any residual thrip eggs in the substrate. 

Lastly, you should regularly inspect your cannabis plants for thrips or other insects. Doing so will not only allow you to spot insects before they start creating a problem, but this will also allow you to spot various other plant problems sooner. 

Here are a few steps you can follow to stop thrips on marijuana plants.

1. Quarantine and monitor new plants

Always ensure you quarantine and inspect new plants before introducing them into your garden. Most growers wait at least a week before confirming that the new plants are good enough to be put with other plants as this period allows them to monitor new plants and look for indicators of thrips or various other parasites. Check the plants extensively, especially the undersides as this is where most pests hide. 

2. Maintain a clean growing environment

Thrips can conceal themselves in even dead leaves and other plant material and reproduce easily. Thus, it’s imperative to clean your grow room frequently to discourage these little monsters. Make sure you remove all fallen leaves and other clutter at least once every week. In addition, clean all your growing equipment including trays and other tools. This way, you discourage the pests from breeding further. 

Thrips can inadvertently be transported on tools, equipment, or even clothing and spread the infestation. It's important to regularly clean and inspect all items used in your garden. Clean pruning tools, trellis stakes, and other equipment after each use with alcohol or a diluted bleach solution. Also, inspect your clothing before entering the grow room to avoid unintentionally bringing thrips or their eggs into the garden.

3. Monitor and identify early signs

By inspecting your plants regularly, you’re already on the path to a pest-free environment. This way, you can identify the signs of any pest invasion before it becomes very problematic. Check the undersides, especially for silver speckles, and damaged or distorted leaves with a shiny or silvery appearance. Look very closely as thrips are very small and fly around undetected. 

4. Use barriers

If you’re growing outdoors or in greenhouses, use physical barriers to prevent thrips. These barriers include mesh screens or even nets that you can place around your plants so the pests can’t access the plants easily. 

5. Introduce beneficial insects

You can use beneficial insects that prey on thrips as an eco-friendly way to get rid of them. Predatory mites, such as Neoseiulus cucumeris, are commonly used to control thrips. These mites prey on thrip eggs and nymphs, helping to reduce their population. Ladybugs (lady beetles) are another option as they feed on thrips at various life stages. Introducing these beneficial insects into your cannabis garden can help maintain a natural balance and prevent thrip infestations

Summary: How to Deal With Thrips On Cannabis Plants?

Thrips are notorious creatures that steal essential nutrients from your cannabis plant by sucking the sap out of them. Over time, these tiny insects can cause significant damage to your cannabis plant, which can hamper their growth and yield. If the problem still persists, thrips can eventually kill your plant, too. 

Fortunately, thrips are easy to get rid of with the right methods. Remedies like Bt, neem oil, insecticidal soap, spinosad, diatomaceous earth, and predatory insects are quite effective at killing thrips. And preventing them is even easier with timely inspection, cleaning the grow room, and maintaining ideal environmental conditions in the grow room.

But thrips are only one of the many harmful pests that can affect your cannabis plant. Stay tuned to know more about how to deal with other problematic pests while growing cannabis.