How to Get Rid of Spider Mites on Weed Plants

A woman holding three nuggets of dried marijuana leaf.

Spider mites are any marijuana grower’s worst nightmare. This is because these pests are very difficult to eradicate. Many varieties of spider mites exist, but the worst by far is the two-spotted spider mite. This particular breed loves marijuana plants, so if you see one, you must come out with all guns blazing.

Related: What Are Sugar Leaves on a Cannabis Plant?

How to Identify Spider Mites

It is best to be aware of a spider mite problem before your weed plants are extensively affected, so we recommend using A Pot for Pot’s smartphone camera lens (included in our Complete Pot Grow Kit) to observe the underside of the leaves when you’re inspecting your plants.

If you see tiny insects (approximately 0.04 of an inch), as well as extremely tiny and translucent eggs, you might be having an infestation brewing up.

Your suspicions can be further confirmed if you see tiny webs running from one leaf to another. Those webs are why these mites are called spider mites. The webs help protect the colony from dropping to the ground or being blown away by the wind. Yes, a colony.

Additionally, you may see tiny white spots on the leaves. Those spots mark the places where the mites have been feeding on the chlorophyll inside the leaves.

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Macro of a spider mite on a plant.

Why Are Spider Mites Dangerous?

There are two key reasons why you should worry when dealing with a spider mite infestation. 

Disrupted Photosynthesis

First, as we have mentioned earlier, these pests feed on the chlorophyll within the leaves of your plants. Chlorophyll is essential for photosynthesis, which is how plants manufacture their food. When chlorophyll is destroyed, the plant gradually starves and can quickly die off.

Therefore, an infestation of spider mites has the potential to kill your plants if you don’t act quickly.

Developing Resistance

The second reason why spider mites are a problem is that at certain points in their life, they are immune to most killing methods. Much of this is because they are easier to identify once they are adults.  They also may develop resistance if you don’t kill them all on the first attempt. If they return, you will need a new way to kill them.  

Spider mites only need a few days to move through their entire life cycle, from being an egg to being able to reproduce. Once an egg hatches into a larva, it feeds for a few days, then hides away for a few days before a nymph emerges. That nymph, in turn, feeds for a few days before again hiding to mold into another nymph stage. The adult then emerges like a weed-devouring Spider mite butterfly. 

Given that an adult female spider mite can lay at least ten eggs daily, an infestation can become full-blown in a matter of days putting your plants at high risk of being destroyed. Plus, their life cycle also makes it difficult to know when they are all gone.  Say, for instance, you spray and kill off all the adults, you may not know that there are eggs or nymphs still there. Then, the next wave of spider mites emerges resistant to the treatment method you have been using.

That is why you can’t just kill them and forget them. You have to take a long-term approach and kill them multiple times.

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How to Eradicate Spider Mites from Weed Plants

Use ladybugs. Ladybugs are natural predators of spider mites, and they may show up on your weed plants once a spider mite population gets underway. However, the ladybugs are likely to leave as soon as the spider mites have been eaten, so you may need to buy more ladybugs in case a new wave of spider mites, such as the immature ones that survived the initial feeding frenzy, show up.

Use a vacuum cleaner. Perfect for a single Pot for Pot, get a handheld vacuum cleaner and pass it over the top and underside of all leaves of your plants. Carefully transfer the contents of the vacuum bag into a plastic container that you can seal, and then put that sealed container in your freezer. The extreme cold will kill all the spider mites, and you simply throw the bag in the trash. The key advantage of this method is that all the lifecycle stages (from eggs to nymphs and adults) of the spider mites will be targeted by the vacuum cleaner.

Prepare homemade killing solutions. You can also mix some solutions that will kill spider mites. For example, make a bleach solution containing a tablespoon of bleach in a gallon of 95°F water. Another one to try is at least three parts water with no more than seven parts of alcohol. 

Spray this solution on your plants in the evening once temperatures have dropped. Other DIY solutions include nicotine tea, homemade pepper spray and other mixtures, whose recipes you can find online.

Use a commercial spray. If making DIY solutions to kill spider mites isn’t your cup of tea, or you are dealing with a serious infestation that requires decisive action, a commercially available contact spray might work more in your favor. Many of these are easy to find online, or at any agricultural supply store. If you use these, make sure you are thorough. The spray is only effective on the spider mites it gets in contact with. The others will probably become resistant. 

A close up of a marijuana leaf.

A close up of a marijuana leaf.

Final Tips

Rotate several eradication methods to avoid the development of resistance to one particular method. For example, you can use one homemade spray for three days and switch to another for the next three days.

Don’t let your guard down just because spider mite activity appears to have stopped. Remember, spider mites reproduce rapidly, so a sustained campaign against them will help to kill off the infestation in all their different life stages.

Choose all-natural sprays when possible. The active ingredients in whatever spray you use will linger within the plant. If those materials are not safe to eat, they could potentially make the weed dangerous to consume. If you use sprays, follow the instructions and always flush your plants thoroughly. 

Although they can be dangerous, a spider mite infestation doesn’t necessarily mean there’s no harvest coming. However, you will have to fight. The best offense is defense by identifying them early. When you grow with A Pot for Pot, it’s easy to go into full-on investigation mode.  Our smartphone camera lens lets you zoom in on your plant, snap a picture, and inspect it – just to be sure. If there’s something on your plant, we make it easy to see it. 

Related: How to Tell the Difference between Male and Female Marijuana Plants

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Frequently Asked Questions about spider mites

How do you get rid of spider mites naturally?

The easiest way is to mix one part rubbing alcohol with one part water, then spray the leaves.

Will vinegar kill spider mites?

Mix 1/4 cup apple cider vinegar (white vinegar is fine too) with 1 cup of water, 1 table spoon of baking soda & a few drops of mild dish soap into a spray bottle. and then spray it on your marijuana plant

At what temperature are spider mites most active?

They are most active between 48 °F and 111 °F; however, they prefer temperatures between 55 °F and 98 °F.

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