How to Rid Your Cannabis Plant of Spider Mites

In Common Marijuana Insects and Pests to Look Out For we mentioned that spider mites are one of the most common pests that can plague your marijuana. These pests are a particularly big problem since they are almost invisible to the naked eye and also one of the fastest to multiply. 

Since spider mites attack several hundreds of plant species, it is fairly easy for you to carry them to your marijuana plants. These are so common and so difficult to spot that it’s even possible to get them from produce that you buy.

How to identify spider mites

CSIRO, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons

You can only typically identify spider mites after they’ve already multiplied and the plant is already taking damage. Cannabis plants infested with spider mites will have some distinct spotting on their leaves. These marks, called stippling, can be mistaken for nutrient deficiency, but are actually caused by the mites feeding on the plant’s cells. You may also notice webbing all around the plants, which will not always be obvious since it is very fine and may only appear when you spray your plants.

You can only really see a spider mite using a magnifying glass. One very distinct feature they have is the two dark spots on their semi-transparent bodies which are often colored green to yellow-orange. Check out the video below to see just how small they are!

Spider mite larvae only have 6 legs but when they start to become nymphs they grow two more legs for a total of 8, hence the name.

Why are spider mites bad

Spider mites are particularly despised by growers since they are hard to spot, multiply rapidly, and are hard to get rid of. This is another good reason why pest management should be preventative. 

Spider mites feed on chlorophyll, destroying the cells on the epidermis of your plants. The damage they inflict on the leaves and stems can slow down photosynthesis significantly. They will also cover your buds with fine silk webbing, making them unusable. Even though they eat up plants cell by cell, these mites multiply so quickly that a really bad infestation can consume a whole plant within 1 to 2 days. A single female spider mite can lay hundreds of eggs in its lifetime which lasts around 21 days in hot and dry environments. Meanwhile, the eggs hatch in a mere 2-4 days then develop into nymphs in 2-4 days. 

What’s worse, these pests have a zombie-like ability to bounce back from eradication. You have to make sure that you exterminate spider mites on the first try since they can build up resistance to pesticides. This can be hard because after treatment, it can appear as if the mites are gone, but they can come back in a couple of days, already resistant to the pesticide that you used.   

When you might notice spider mites

Spider mites on a leaf
Spider mites seen with the naked eye (black dots on hanger)
Damage caused by spider mites on a leaf (Stippling)
Spider mite colony, Tetranychus. Rose leaf covered with microscopic web of spider mite colony , Plant disease

Adult spider mites measure only up to .5mm, making them practically impossible to spot without a magnifying glass. However, you may be able to notice a group of dots under the leaves of your plants accompanying the stipple marks. Of course, the fine silk webbing is a dead giveaway, but you’re most likely dealing with an infestation when you notice it.

Organic methods to deal with spider mites

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

  • Preventive methods – When dealing with pests that are practically invisible and spread like wildfire, preventive measures are your best bet. Spider mites like dusty and overwatered plants, so make sure to tend to your grow area correctly and religiously. Also, maintain adequate air circulation around your plants since spider mites have difficulty mating under windy conditions.  
Mick Talbot, CC BY 2.0 https://creativecommons.org/licenses/by/2.0, via Wikimedia Commons
  • Natural predators – Since spider mites are really small, they can be difficult to remove manually. Beneficial insects such as the minute pirate bug, ladybug, assassin bug, and green lacewing prey on spider mites and other pests. However, predatory mites seem to be more effective than generalist predators since they also eat spider mite eggs. There are several types: Phytoseiulus persimilis, Typhlodromus pyri, Neoseiulus californicus, Amblyseius andersoni, Neoseiulus fallacis, Mesosiulus longipes, and Galendromus occidentalis. Natural predators are best used when the pest threat is still low to medium.

  • Spinosad & soap spraysSpinosad and soap sprays can also kill spider mites since it dissolves the waxy coating that protects them from dehydration. However, this won’t eliminate the mites hiding in the soil or roots.

  • Natural pesticides – Organic pesticides like neem oil, pyrethrins, azadirachtin and horticultural oils will also kill adult mites, larvae, nymphs and eggs on contact. However, miticides should only be used as a last resort during the flowering phase. Some examples are Essentria IC3 and Azamax
  • CO2 blast – Some growers swear by the CO2 enrichment method, since it doesn’t seem to have any drawbacks. However, a CO2 blast will only kill spider mites and not their eggs so you need to do it every few days. Be extremely cautious when using this method since a CO2 concentration above 5000 ppm is hazardous to humans.

Non-organic methods to deal with spider mites

Even though spider mites are difficult to deal with, preventive measures and natural control methods are still enough to address an infestation. Non-organic methods are practically unneeded when growing marijuana but illegal growers typically use them to salvage their crops. Here are some banned chemical and products that are used on cannabis that you need to watch out for:

  • Dichlorvos
  • Bifenthrin
  • Avid
  • Floramite
  • Shuttle
  • Telstar
  • TetraSan
  • Hexygon
  • Forbid
  • Judo

Frequently Asked Questions on Spider Mites

How fast do spider mites reproduce?

A single female spider mite can lay hundreds of eggs in its lifetime which lasts around 21 days in hot and dry environments. The eggs will then hatch in a mere 2-4 days then develop into nymphs in 2-4 days. 

What are signs that you have a spider mite infestation?

Plants with spider mites will typically show stippling on the leaves which can be mistaken for signs of nutrient deficiency. You may also see fine, silky webbing all around the plant.

Are spider mites harmful to cannabis plants?

Spider mites devour plant cells, reducing your plant’s ability to photosynthesize. Full-blown infestations can devour a whole plant in 1 to two days.

Conclusion

Because they are almost invisible to the naked eye and can be carried on practically any agricultural material like mulch, it’s easy to get spider mites on your plants. However, a well-maintained growing environment will make your plants inhospitable to these tiny pests. Keeping some ladybugs as a preventive measure will greatly minimize the possible proliferation of any mites you may have carried. You should also constantly watch out for telltale signs so you can use predatory mites at the right time before a full-blown infestation and don’t be afraid to cut or separate any plants that are already infected. Lastly, natural pesticides are quite effective but they are not ideal especially during the flowering stage. These treatments are likely to leave chemicals on your plants so they should be used as a last resort.   

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