How to Rid Your Cannabis Plant of Thrips

In Common Marijuana Insects and Pests to Look Out For we mentioned that thrips are one of the most common pests that plague marijuana. These pesky insects may not be as bad as spider mites but they can still destroy your plants completely if left unchecked. 

There are thousands of species of thrips (Thysanoptera) and although some have their place in the ecosystem as predatory insects that eat mites and pollinators, most are more troublesome than helpful. These pests are able to reproduce asexually, multiply rapidly and squeeze their way into the tightest of spaces to invade your grow room. Some even carry viruses around, like the Tospovirus, Ilarvirus, Carmovirus, Sobemovirus and Machlomovirus. They are also annoyingly fast, making them difficult to get rid of.  

How to identify thrips

Daiju Azuma, CC BY-SA 2.5 https://creativecommons.org/licenses/by-sa/2.5, via Wikimedia Commons

The species of thrips that infest cannabis usually appear black, brown, golden or pale yellow slivers as thin as a needle. The most damaging thrips species is the Frankliniella occidentalis which are colored yellowish-white. They lay their eggs on the plant itself.These pests measure only 0.5 to 2.5 mm long so they are barely noticeable unless in groups.  

Frank Peairs, Colorado State University, Bugwood.org, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons

Under the magnifying glass, thrips look somewhat like lobsters with antennas. They have 6 legs and a long abdominal segment. Nymphs are often lighter in color and adults tend to be darker and while these insects have wings, they are not used for flying but rather for darting around. You can usually find thrip eggs on the underside of the leaves.

Why are thrips bad

Thrips typically attack cannabis plant leaves, injecting cells with enzymes that dissolve plant matter. These insects then suck this nutrient-rich liquid out, leaving damage that may look like spots, streaks, silvery speckling, or small white patches, a bit similar to what spider mites do. Thrips will literally suck the life out of your plant’s leaves, hollowing it out and impairing its ability to photosynthesize.

While thrips primarily attack leaves, they are also known to damage stems and lay eggs in the softer parts of the stem. Some species even strike at the roots of your plant which can be a pain to identify, but good preventive practices such as not overfeeding or overwatering your plants will significantly  

When you might notice thrips

Thrips can be hard to spot, especially if there are still a few of them, but they are not invisible. You may notice really tiny slivers on your plant, accompanied by stippling or dark spots on the leaves. These pests will also congregate on the underside of the leaves and lay their eggs inside soft plant tissue. 

Thrip eggs, larvae and adults

You may easily overlook the presence of a few thrips but they will definitely make their presence obvious in a week. Adult female thrips can lay 150 to 300 eggs within its 21-day lifetime and in turn, these eggs hatch within 2 to 4 days. Once hatched, it will only take 6 to 10 days for the instar larva to become adults.  

Organic methods to deal with thrips

Fortunately, organic pest control methods, when done correctly, will be enough to take care of a thrips problem. You’ll also likely eliminate other pests in the process. Here are some well-known natural ways to prevent and control thrips on your cannabis plants.

  • Natural predators – Introducing natural predators into your grow area is a good way to prevent or manage a thrips problem. You can introduce generalist predators like lacewings and ladybugs if you’re dealing with other pests, but if you want to deal with thrips specifically, you need to bring in predatory mites that eat the eggs and larva of thrips. Here’s a list of predatory mites that will attack thrips and other mite pests: 

You can also introduce beneficial nematodes (Steinernema feltiae) to deal with thrips residing in the soil.

  • Spinosad & soap spraysSpinosad is an effective insecticide and will also kill thrips on contact and ingestion. Soap sprays can also kill thrips since it dissolves the waxy coating that protects them from dehydration. 

  • Sticky trapsSticky insect traps are also somewhat effective against pesky adult thrips that move around. However, this won’t totally eliminate these pests, so use sticky tapes to supplement other methods, preferably before you introduce beneficial insects.  

  • Natural pesticides – Organic pesticides like neem oil, pyrethrins, azadirachtin and horticultural oils will also kill thrips on contact. However, pesticides should only be used as a last resort during the flowering phase. Some examples are BotaniGard ES and Azamax

Non-organic methods to deal with thrips

With proper pest prevention and management measures in place, thrips will rarely be a problem bad enough that it will require synthetic pesticides. Besides, the use of non-organic methods to control thrips in a home grow context is almost never justified. Here’s a list of non-organic pesticides used on thrips that are not recommended due to the harmful effects they may pose to humans and other beneficial insects.

  • Dichlorvos
  • Acephate
  • Malathion
  • Dinotefuran

Frequently Asked Questions on Thrips

How fast do thrips reproduce?

Adult female thrips can lay 150 to 300 eggs within its 21-day lifetime and in turn, these eggs hatch within 2 to 4 days. Once hatched, it will only take 6 to 10 days for the instar larva to become adults.  

What are signs that you have a thrips infestation?

Thrips damage leaves by injecting it with enzymes that can break down plant cells. These pests then suck out and ingest the liquefied matter as food, leaving a hollow spot on the leaf.

Are thrips harmful to cannabis plants?

Colonies of thrips can damage the leaves of a cannabis plant so bad that it won’t be able to photosynthesize, impairing its growth and ability to bear buds.

Conclusion

Thrips will cause significant damage to your cannabis plants only if you let an infestation run its course. As always, preventive measures such as avoiding overwatering and overfeeding, using a sterilized growing medium, maintaining a clean growing area etc. will make it difficult for thrips and other pests to thrive. You should also make it a point to regularly check your plants for any discoloration or weird marking on the leaves. Using a magnifying glass to closely inspect these irregularities will help you distinguish if the markings are caused by a pest or nutrient deficiency. 

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