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Using Natural Pesticides and Repellents for Common Cannabis Problems

June 7, 2016

“Natural” means different things to different people. Typically, when we think of “natural” we imagine roots in the dirt, water flowing over riverbeds, flowers blooming wild in a field or something similar. “Natural” in industry usage, such as on a product label, is often meaningless to the point of absurdity.

For the purposes of this article, “natural” will refer to any substance that is not synthetically produced; i.e., using chemistry to create new chemicals. “Natural” will include products and their byproducts manufactured without the use of synthetic chemistry, although components extracted with chemistry will remain.


For Powdery Mildew

Powdery mildew (PM) is probably the greatest bane of any cannabis farmer. At first glance, the stuff looks like trichomes, but inhaling a lungful of PM can prove deadly for some people, especially patients with compromised immune systems. One case of PM can quickly spread to an entire crop, jeopardizing grow rooms and rendering pounds of good bud utterly useless.

The simplest natural remedy for PM is good ventilation. As long as new air keeps circulating into the grow area and humidity is kept under control, PM shouldn’t happen. In an age of heavy regulation for licensed cannabis businesses, most professional grows must be done indoors. But growing indoors is the single biggest factor for generating PM. Keeping plants spaced apart, watering only when you know the plants will receive at least five hours of light, and maintaining clean growing areas are other solutions for preventing PM.

But things happen. In the event that you get PM on your plants, immediately remove all infected buds and leaves with clippers and discard the clippings in a plastic bag. Take care to prevent the spread of spores. Spray the remaining stems, stalks and other parts of the plant with the following mixtures:

1.       Hydrogen peroxide and water (1 tablespoon per gallon) to kill the PM and

2.       Limonene and water (1 teaspoon per pint) to control the spread of PM in the future

Some growers suggest using neem oil to control PM. Although neem oil can be effective, it has a fairly distinct odor and flavor that cannabis connoisseurs can easily pick up on. Since neem oil can also be used to repel spider mites, it’s best to reserve it for the bugs and rely on other methods for controlling PM.


For Spider Mites

A spider mite infestation resembles a horror film. These little creatures can reproduce at an exponential rate, dropping eggs and incubating them faster than most pesticides can stop them in their tracks. Even with harsh synthetic insecticides, they can keep multiplying, giving them a reputation of being zombie-like. Spider mites are also known to disappear for a short time, giving growers the false confidence that they’ve ended the infestation – only to return with a vengeance. If a grow isn’t careful, the spider mite eggs can latch onto clothes and spread to a grower’s car or home.

The best way to prevent spider mites is to either cover or replace your clothes before entering a grow. Growers who live with children, dogs or cats are at a higher risk of transferring spider mites to a grow. Clones or plants in vegetative stage purchased or received from another grow may also have spider mites, so be sure to inspect any clones or plants before bringing them into the grow area.

The best weapon against spider mites is prevention. If you anticipate you may have a risk for spider mites, try dusting off the surfaces of the floor, plants, windowsills, countertops, etc., with diatomaceous earth. These are sharp, microscopic crystals that will tear apart the mites’ exoskeletons. The great thing about diatomaceous earth is that it’s completely harmless to humans and pets.

Another level of control is introducing ladybugs on your plants. These are one of the spider mite’s natural predators. However, ladybugs are pretty slow at their job, so taking on a full-fledged infestation with another bug won’t succeed. Ladybugs are best for small, manageable infestations or for general prevention.

To combat the bugs, you have a few options:

Rubbing Alcohol

A mixture of 60% alcohol, 40% water should be safe for your plants and working environment but will also be concentrated enough to kill the mites and their eggs.


Bottles of spinosad mixtures contain chemicals produced by bacteria. These particular chemicals are harmless on people, plants and most animals, but they get rid of mites.

Neem Oil

Mentioned earlier, neem oil comes from the neem tree. It has an unpleasant smell and taste, but it keeps mites off the plants.


SM-90 is a mixture of plant oils and is known to repel and kill insects and arachnids. SM-90 also smells much sweeter than neem oil, so if copious amounts of an oil are required, it might be best to go with SM-90 over neem.

The major downside to a spider mite infestation is that sometimes “natural” and “organic” methods just won’t get the job done. You’ll likely need to combine some or all of these methods to get rid of mites, but if all else fails, you may need to resort to a heavy “pesticide bomb” and simply spray the entire grow. This is not the preferred method, but sometimes it’s the only way to save the plants. Of course, only use substances that are allowed by regulatory authorities.

Just remember: Prevention is your best weapon. The more you invest in keeping PM and mites out of the grow to begin with, the fewer headaches you’ll have to deal with in the long run.


By Randy Robinson
Image Credit: CSIRO

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