Plantalk Colorado’s issue 1427 covers the topic of natural pesticides very well.
When a pest or disease is devastating your plants, refrain from grabbing the strongest chemical you can find. Always try simple and safe controls before using any pesticide. For example, sometimes a strong blast of water from a hose is all it takes to get rid of a pest. You can also hand-pick pests like caterpillars and drop them into soapy water. Or shake Japanese and potato beetles off plants onto a sheet. And aphids, cabbage worms and white flies are attracted to yellow so they can be trapped by covering a piece of yellow poster board with sticky glue and hanging it among the infested plants.
If physical controls don’t work, the next thing to try is a homemade organic pesticide. Homemade preparations are generally milder than commercial pesticides. For example, garlic makes an effective spray for most insects. Simply puree 15 garlic cloves and one pint of water in a blender, strain the mixture through a cheesecloth into a clean spray bottle, and apply to the tops and bottoms of all leaves. Repeat every few days until the problem is gone.
If homemade sprays are not strong enough, you may need to buy an organic pesticide. Horticultural oils, insecticidal soaps and botanical insecticides are all organic pesticides. Most are safe to use on food Crops because they break down quickly and have no long-lasting effect on the environment. Nonetheless, they should be used as a last resort. Because they’re not only toxic to the pests and diseases you are trying to eradicate, they can also be toxic to insects, birds and soil microorganisms that are part of a healthy Garden.
Before applying anything to your Garden, identify the pest and disease you want to control so you can choose the most effective product. And always read the label and follow directions exactly.