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Pest Guide – Thrips

Pest Guide: Thrips

There are many kinds of pests that can damage a cannabis crop, but few are as damaging as thrips. Thrips are a common pest and are tough to eradicate from a garden once they have taken hold. One of the most unique things about thrips is that they are frequently found in both indoor and outdoor gardens. Even more unusual is that these insects thrive best indoors, so indoor growers will need to be vigilant in checking for them.

What are Thrips?

Thrips are tiny, measuring at less than one-quarter on an inch when they are fully grown. They can range in color from translucent to straw-colored, light green, or black. They have two feathery wings, though they lack the ability to fly. Instead, they rely on the wind to carry them between locations.

Female thrips have the ability to produce eggs without the presence of a male. They hollow out the stem or stalk of a plant and lay their eggs inside of it. They use the plant as shelter from the elements and predators, and as soon as the eggs hatch, they begin to feast on the plant matter surrounding them. The eggs are tiny, making them difficult to see, so cannabis growers need to watch for thrips in their larval stages.

Thrip Damage

Thrips are extremely active insects that feds in large groups and will hop out of sight quickly when disturbed. They feast on the liquids inside of a plant by using their mandible stylet to poke a hole in the plant. Thrips may cause visible plant damage, but that is not their most dangerous feature. Thrips spread tospoviruses, which are some of the most damaging plant viruses in existence.

Signs of Thrips

Once thrips are fully grown, they are easier to identify. However, they are still very small and those in the larval stages can blend in with the color of the cannabis plants. Thrips typically infest the lower portions of a plant, but their slender body shape makes it easy for them to hide. Even if there are no thrips visible, there are other signs that cannabis growers may have a thrips infestation, including:

Silver Trails

As thrips begin to feed, especially when they are in their younger stages of development, they may leave a silvery trail behind them similar to a snail’s trail. This trail may be difficult to see initially, so growers should inspect the leaves of their cannabis plants closely.

Discolored Spots

As a thrips infestation progresses, discolored spots will flank the silvery trails. These spots will be light brown with a slight sheen to them. Eventually growers may notice small black spots on their leaves, which are the feces left behind.

Brittle, Dry Plants

If the thrips infestation becomes advanced enough, the cannabis plants will become dry and brittle. This is because the thrips have robbed the plants of their chlorophyll as the pests have feasted on the plant’s liquids. Once the infestation has progressed this far, it is difficult for the plant to repair.

Protecting Cannabis Plants from Thrips

Thrips infestations come on quickly and get out of hand fast. The best way to prevent devastating damage from these pests is to prevent an infestation from ever occurring in the first place. Still, here are some methods growers can use to eliminate a thrips once an infestation has taken hold. Below is a list of the best ways to prevent or treat a thrips infestation.


An ounce of prevention is worth a pound of cure, and that is especially true for thrips. Prevention takes less work than trying to control an established thrips infestation, so growers must take the proper precautions when setting up their grow area. To prevent a thrips infestation, do the following:


When first setting up a grow room, growers will need to sanitize everything in the room thoroughly, especially in between grow cycles. They must take care to sanitize tools for trimming and pruning, as well as any tools used for planting. Sanitizing these tools should kill any adolescent thrips that may be hiding out in the grow room.

Keep the Grow Area Clean

Since thrips are difficult to see, it is vital to keep the grow area as clean as possible. This includes removing any dead plant material from the room and disposing of it elsewhere. Those growing cannabis outdoors should be sure to remove any weeds that may be near their plants, as these weeds can harbor thrips. In general, spending some time in the grow area every day will help to keep it clean and prevent any major issues.

Install Insect Adhesive Strips

Once the growing setup is complete, growers should install insect adhesive strips in the area. These adhesive strips will trap any bugs in the area, including thrips, which will help prevent infestations from taking hold.

Install Thrips Nets

One final method of prevention is to install thrips nets. Indoor growers can use these over any vents in the room to prevent entry, whereas outdoor growers can use them as row covers. When used outdoors, this also prevents any other insects from entering the grow area and keeps birds at bay.

Treatment for a Thrips Infestation

Once a thrips infestation has started, growers need to act fast to prevent devastating damage to their cannabis crop. Once the infestation has gone too far, there is not much the grower can do to save their plants. To eradicate thrips, growers can do the following:

Use Insecticidal Soap

Insecticidal soaps work by weakening thrips’ outer shells. Though they are deadly for these insects, they are considered safe for humans. Growers will need to spray down their whole plant as thoroughly as possible. If they do not cover the entire plant, some thrips may survive, and because thrips can reproduce asexually, even one can start a new infestation.

Another important thing to keep in mind when using insecticidal soap is how long it lasts on a plant. Typically, the soap residue is done within one day, so multiple applications will be needed to ensure the plants’ survival.

Use Spinosad Products

The best chemical options for treating a thrips infestation are spinosad products. These products are completely organic and harmless to plants, children, and pets. These products can be applied liberally to both the plant and the roots with no negative consequences. They can be added to water used on the plants, eliminating thrips systemically through the root system.

Spinosad products are made by fermenting a certain soil bacteria called actinomycete Saccharopolyspora spinosa. When thrips ingest the products, their nervous system is interrupted, resulting in death. This is an ideal option for outdoor growers, as these products are not toxic to many other insects.

Use Neem Oil

Neem oil is an effective method of treating insect infestations, but it leaves a nasty smell and taste on buds. It is critical that growers do not get neem oil on their buds. Because thrips love to feast on the buds of cannabis plants, this method is best used on plants that have not entered the flowering stage.

Neem oil is also an effective treatment for certain molds that may grow on cannabis plants. When treating the plants with neem oil, it will need to be applied with a mister, and must be applied during a time of day when the sun is least intense. Growers should use personal protective equipment, as some research has suggested that neem oil can be harmful to humans.

Use Pyrethrins

Pyrethrins are also effective chemicals used to eliminate thrips infestations. Like neem oil, these products need to be applied with a mister. They lose their effectiveness after a day or two, so they will need to be applied periodically to maintain effectiveness. While they are not considered harmful to humans, they are deadly to bees, so outdoor growers should avoid using them as much as possible.

Introduce Natural Predators

One chemical-free way to handle a thrips infestation is by introducing natural predators. Other insects, such as minute pirate bugs, ladybugs, and lacewings. Minute pirate bugs feed on eggs and larvae, so they can prevent an infestation before it gets too far along. Ladybugs and lacewings feast on all stages of thrips growth and are especially effective for indoor grow rooms.

For maximum effectiveness, beneficial insects should be released after treatment with a chemical that kills thrips but is safe for other insects. Generally, using multiple methods to combat thrips is the best way to prevent severe damage and get the infestation under control.

Bottom Line

Thrips are a serious problem for cannabis growers, and one that needs to be handled as soon as possible. Left unattended, it does not take long for thrips to destroy a cannabis crop. Growers should scan their plants frequently to keep an eye out for developing infestations and act fast if they notice any signs of thrips. Beware of overfertilization and over watering, as thrips love feeding on nitrogen-rich plants and excess water creates the perfect environment for thrips’ reproduction.