Gardeners have been making their own pesticides for hundreds of years. Many were based on what the inventor imagined would repel insects. Some were sufficiently revolting to repel anything. A few actually worked, and still work today. Follow some important guidelines in making your own pesticide.
Organic and Deadly
Just because a pesticide is homemade, from organic ingredients, does not mean that it is harmless to people, pets or beneficial insects. If you get hot pepper spray in your eyes it can easily cause permanent damage. If you breathe in some home remedies you could end up in the emergency room of the nearest hospital. And if you or your pet ate or drank one of these, it would certainly be painful--and might be fatal.
So treat these concoctions with the respect they deserve. Wear disposable rubber gloves when you are mixing them, and protect your eyes with goggles when you spray them. This isn't a joke: the combination of some common household items can be deadly, to you or your pets.
Most of these pesticides will kill beneficial insects such as honeybees, praying mantises and ladybugs, so take care when you spray.
Choose the Target
The insects that cause gardeners the most grief are those that eat leaves, such as the adults or larvae of Japanese beetle, Colorado potato beetle, and flea beetle. What you want to do is either kill the insect, or at least stop it eating your plants. The first option involves strong substances. Something strong enough to kill a healthy beetle can hurt you, too. There are non-chemical ways to kill beetles, such as handpicking them into a bucket of soapy water, then flushing them down the toilet.
When insects munch a leaf, they want it to taste like, well, a leaf. So if you spray their dinner with hot pepper or garlic, they are likely to go find another garden to munch on.
Try mixing a teaspoon of Tabasco® sauce with six garlic cloves and a cup of water. Blend in a kitchen blender or food processor until the garlic is pureed and invisible. In a quart bottle, mix this solution with 3 cups of water and let it stand for at least one hour. Carefully strain it through a double layer of cheesecloth or a coffee filter. Add a single drop---no more---of dish detergent and stir. Spray it on the tops and undersides of the leaves.
If you hand-pick Japanese beetles and drop them into soapy water, biologists theorize that the beetles emit fear pheromones as they suffocate in the water.
If you pour about two cups of these beetles into a blender even more fear pheromones are created when you hit the "On" button. Filter the beetle water, then dilute it with 6 cups of clean water. Spray on the plants being attacked by Japanese beetles. This will repel beetles, which is not really surprising.
You may like garlic, but insects don't. Puree three or four cloves of garlic in a cup of water, then pour into a 1-quart container. Add 3 cups of boiling water, mix well. Allow to stand overnight, then filter (double cheesecloth or a coffee filter), add one drop of dish detergent, and spray.
This is effective against insects on vegetable and ornamental crops. Flea beetles, corn ear-worms, and cabbage moths are among the species repelled. The garlic smell does not last, and will not affect the taste of food crops.
The Real Deal
Sometimes a mere deterrent is not enough. That's when you might consider using the known killing power of tobacco to save your garden ornamentals. Nicotine tea is simple to make: Soak ½ ounce of pipe or rolling tobacco in a quart of hot water. Allow to stand overnight. Filter (double cheesecloth or a coffee filter), then spray.
Do not use this on food crops, and keep it well away from tomatoes, peppers, eggplants, and potatoes (it can kill them). Keep it off your skin, too.
A non-detergent soap will attack the exoskeleton of many insects, including beetles, killing them quickly. You can make a soap spray by grating about 1/16 of a Fels-Naptha® soap bar into a cup of water. Stir to make a gel. Dilute with 3 cups of hot water, mix well, strain and spray.