Homemade remedies are a longstanding tradition among organic gardeners, who have had to be creative in finding ways to battle insects and diseases without the help of synthetic chemicals. In the case of fighting aphids, or plant lice, two homemade sprays have proven very effective in controlling aphid infestations: tomato leaf spray or garlic oil spray. While knowing how to make and use them is important, it's equally important to understand why they work.
Tomato Leaf Spray
Tomato plants, as members of the nightshade family, contain toxic compounds called alkaloids in their leaves. When the leaves of tomato plants are chopped, they release their alkaloids. When the alkaloids are suspended and diluted with water, they make an easy-to-use spray that is toxic to aphids, but still safe around plants and humans.
To make tomato leaf spray, simply chop one or two cups of tomato leaves and soak them in two cups of water. Let it steep overnight. Strain out the leaves using cheesecloth or a fine strainer, then add another one to two cups of water to the liquid and add it to a spray bottle.
To use the mixture, spray the stems and foliage of the infested plant and pay particular attention to the undersides of leaves since that is where aphids most commonly congregate.
Garlic Oil Spray
Organic gardeners have long relied on garlic as part of their pest-fighting arsenal. Garlic contains sulfur, which, besides being harmful to pests, is also an antibacterial and antifungal agent. The dish soap in this mixture also breaks down the bodies of soft-bodied pests like aphids.
To make garlic oil spray, mince, or finely chop three to four cloves of garlic, and add them to two teaspoons of mineral oil. Let this mixture sit for 24 hours. Strain out the garlic pieces, and add the remaining liquid to one pint of water. Add one teaspoon of liquid dish soap. This mixture can be stored and diluted as needed.
Before using this spray test it by spraying an inconspicuous part of the plant. If there are no signs of yellowing or other leaf damage after a day or two, it is safe to use. If there is leaf damage, dilute the mixture with more water and try the test again. Once you have determined that it will not harm your plant, spray the entire plant, paying particular attention to the undersides of leaves.
A word of caution about this spray, garlic oil can be harmful to beneficial insects (such as ladybugs, which are natural predators of aphids) just as easily as it kills the bad guys. It is best to keep as many beneficial insects around as possible. This spray should only be used if you have not seen any beneficial bugs in your garden. Otherwise, you should use the tomato leaf recipe, which will not harm beneficial bugs.
Other Natural Methods
Sometimes, a strong blast of water from the hose will knock the aphids off of a plant and solve the problem. Just make sure the water is not too strong that it uproots the plant or overwaters it.
Try to attract beneficial insects like ladybugs, lacewings, parasitic wasps, or damsel bugs to your garden. They will attack the aphids. Plant mint, fennel, dill, yarrow, and dandelions to attract these beneficial predators to your garden.
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Omar, SH., Al-Wabel, NA. Organosulfur Compounds and Possible Mechanism of Garlic in Cancer. Saudi Pharmaceutical Journal, 18,1,51-58, 2010, doi:10.1016/j.jsps.2009.12.007
Almanac, Old Farmer’s. “Aphids.” Accessed August 17, 2021. https://www.almanac.com/pest/aphids.