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First published 2nd November 2021


I’d never be without this classic remedy for arthropod pests. Simple and dirt-cheap to make, lasts forever, and with the added bonus that arthropods* can never develop resistance to it.

First, the recipe:

Half cup detergent to two cups any vegetable oil (don’t waste your good stuff — the cheapest no-name you can buy does just as good a job!)
Shake well until solution turns milk-white, as seen in the 500 mL bottle at left in above photo.

This is your concentrate and will last a very long time.

How to use:

Add one tablespoon to 500ml water in a spray bottle like the one at right in the above photo.
Spray all over pests such as aphids, mites, scale, mealybugs, stinkbugs…

How it works:

Arthropods exchange gases through spiracles, or small holes, along their abdomens. Suffocation occurs when these spiracles are blocked — something an arthropod cannot evolve a countermeasure to.

White oil acts by blocking these holes — the oil does the blocking and the detergent is the ‘glue’ by which the oil sticks to the body long enough to cause suffocation.

Important:

It is best to spray after the heat of the day has passed, or when temperatures are below 25 – 30°C, as this prevents foliage overheating.

Overheating occurs when an oil drop acts like a lens by concentrating light energy onto a small piece of plant tissue.

It doesn’t matter how late in the day you spray, as the arthropods aren’t going anywhere and are always breathing! White oil will work throughout the night just as well as in daylight.

I keep saying ‘arthropod’ whereas others would say ‘insect’. But mites are arachnids, and related to spiders, scorpions and ticks. Insects are arthropods, and arachnids are arthropods, therefore ‘arthropod’ is just a more accurate word to use!

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