Growing indoors, I am eventually plagued by spider mites at least once a season. It’s always discouraging when those small strands start appearing between branches. I usually start a new internet search, re-reading all the things I’ve already tried before, hoping to find something new. I tried all the concoctions that are safe for use indoors, and around fish, and while they inhibit the spread, the continuous applications are exhausting.
This last time around was different. This time they were growing on my key lime tree, that I had grown from seed, and is now over 3 years old. It was just recovering from larval gnats that almost killed it. It lost nearly all it’s leaves and I pruned it back to ease up demand on the remaining roots while they grew back, and to stimulate some re-growth of branches. There was no way I was going to let spider mite’s kill this tree. They were also on my Aleppo Pepper, and they love to kill my peppers.
I was reading about diluting alcohol and spraying that on plants to dry the insects, OR applying diatomaceous earth to the plant in puffs.
I’ve tried the alcohol spray before, and while it works, it doesn’t get them all, and when you think you’ve killed them all and let your guard down, they always make a resurgence.
I never used diatomaceous earth because the mess of spraying a fine powder that is hazardous to human lungs around the house is a non-starter.
That’s when I got the idea to mix the diatomaceous earth (DE) into the alcohol solution and spray that on the plants. The nice thing about having the DE in a solution is it’s not going to be as big of a breathing hazard, it will go directly where it is targeted without floating off and will distribute on the plant quite nicely. When the alcohol solution evaporates, the powder will remain stuck to the plant, and since it will be dry again, will be effective in killing any insect that walks through it. The alcohol diminishes the number of spider mites, and the DE will continue to kill anything left that survived, or kill anything that hatches later on.
If you spray it indoors, you do have to mop up anything that hits another surface before it dries, or you can let it dry and wipe it up with a wet cloth, but it’s pretty inert, and very easy to clean up, so I don’t worry about spraying it inside.
Recipe for 1 liter spray bottle:
- 200ml 70-99% isopropyl alcohol
- 2 heaping teaspoons Diatomaceous Earth
- 800ml Water
Shake the bottle frequently while spraying to keep the DE well distributed.
Results:
I removed the webs & sprayed both the key lime tree & the pepper plant twice, separated by 24 hours, making sure to coat the undersides of the leaves and all the nooks and crannies. I inspected both plants twice a day after that. There were two occasions where a single thread showed up on the key lime tree. I removed it and gave it a spritz for good measure. The pepper plant never had a single thread come back. After two weeks I used some plain water to gently spray the leaves and rinse off any DE that wants to come off. You can easily wipe it off dry as well. It’s now been 3 months and without any further treatment, there have been no more signs of infestation.
It’s fast, cheap, effective, organic, and I’m happy to finally have something that works against these things.
Hey Mike is this recipe effective on outdoor gardens using food grade DE? My entire garden has them,I think they were in the mushroom soil I had delivered….. Thank you!
As long as it doesn’t rain it should be fine. They can come in on the wind, so if your infestation is outdoors, it is hard to pinpoint the cause.
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Hi Mike, what’s the concentration of the alcohol that you used? Rubbing alcohol 70%? Tq
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I got it, missed the section on your recipe. Thanks!
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I know you mentioned the alcohol evaporating, but does mixing the DE in a liquid solution change its ability to harm the pests? Like breaking down the sharp edges?
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Once it dries it has the same properties as before.
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