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  • Spider mites on cannabis

    Created by Marta Collier on

    I have been growing medical cannabis (with a permit and for personal use only – my husband suffers from seizures and I have fibromyalgia) for some time now and only recently started being plagued by spider mites. I have a number of plants outside in my back yard that have not yet been infested, however, growing right next to my cannabis is a huge tomato plant that now has a fair number of spider mites all over it. I would like to treat this problem with predator mites but I am not quite sure of what type to get. I also have an indoor grow – just a few plants in a bathroom. Spider mites have been a problem in that room for a year now. I am in the Los Angeles CA area, and recently it has been hot – in the 90’s and 100’s, with relatively low humidity. I have also had a problem with cabbage loopers; they are very fond of cannabis as it turns out. Can you make a suggestion as to how I might best get rid of these bugs?

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  • #205563


    Hi Marta,

    Cannabis and tomato plants have very similar growing preferences and characteristics. So regardless of the plant species, cultivation practices should be generally identical.
    As for the spider mites, it would be a good idea to just get rid of that infested tomato plant before the mites spread. If you’re having a hard time chopping that entire plant down, at least remove the highly infested areas of the plant. Spider mites are extremely prolific and multiply crazy fast! Since they are so hard to see you often wont even notice them until they’ve taken over. They are especially happy in a hot and dry environment such as yours, so if they haven’t already, they will spread! Additionally, if you are using other insecticides that are wiping out their natural predators, they are going to blow up pretty quickly as they can easily build up resistance to many of those insecticides. Other factors that encourage the build up of these guys include plant water stress and dust build up on leaves, so be sure to stay on top of that. The next best step to controlling these pests would be to release predatory mites. The species Phytoseiulus persimilis are extremely efficient and should wipe out the population. (It looks like that is the species sold on this website). You could also use lacewings or lady bugs to control the spider mites as some secondary options but the predatory mites are definitely your best bet. However, if spider mite populations are high, you will have the most success if you apply an insecticide a few days prior to the release of the predatory mites. My favorite product for spider mites is SNS 217. It’s an all natural rosemary oil based spray that kills spider mite adults and eggs and it is safe to use in all of the plant stages EXCEPT in flowering and fruiting. (This warning is listed on the bottle, although I have used it moderately in the later stages and saw no repercussions).
    When it comes to the cabbage loopers, as tedious as it may be, the best method/first step of control is to manually pluck the pests from the bottom of leaves and destroy them. Especially if your plants are close to harvest, you want to avoid spraying anything on them. It is also important to remember to remove ALL plant debris throughout the growing season to minimize pest overwintering/survival. After you have manually removed all the caterpillars you can find, you can use a BT or Spinosad based insecticidal spray but ONLY if your plants are still in the vegetative phase. If they have already begun to flower or fruit you can utilize the nearly invisible Trichogramma wasps which will parasitize the cabbage looper egg stages by stinging those eggs and implanting their own eggs that will then kill the pests as they hatch and eat their way out! Additionally, you can prevent the presence of cabbage loopers by spraying diluted neem oil on your plats every 10 days.

    Good luck!!

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