I’d like to start making my own simple insecticides. Which types of homemade garden sprays are actually effective?
Before taking the time to make an insecticide, step back and ask yourself the following questions.
Have you correctly identified the problem? Gardeners can easily mistake injury caused by disease or extreme weather for pest damage. The choice of insecticide, if one is needed, depends on confirming the damage was indeed caused by a pest, and then identifying the pestilent perpetrator.
Are you sure the problem is getting worse? Existing damage won’t disappear, but if new leaves are unafflicted, you likely don’t need to spray. Similarly, if the plant is still growing and producing despite cosmetic blemishes, then taking steps to boost plant growth is a better option than attacking pests.
Do you know which beneficial insects to expect and how to identify them? These advantageous insects are usually present but difficult to see; eggs and larvae are tiny and don’t look anything like adult insects. You want to ensure that, if you do spray, you won’t harm beneficials’ populations. Also, the beneficials may handle the pests for you if given the opportunity and time.
Will other pest control methods work? It depends on the pest, but barriers, traps and other non-pesticidal methods can often perform better than sprays.
If your crops do indeed require an insecticide, the two homemade sprays I recommend are plain water and diluted soap. Strong sprays of water will control aphids, pear and rose sawflies, spider mites, and thrips. For aphids, spray at least twice, waiting two to three days between each spraying. Learn how to create a custom watering wand for this method of organic pest control.
Soap sprays are effective on leaf-eating insects, sucking insects and mites, but only if the spray comes in direct contact with the pests. Use only pure soap, such as Dr. Bronner’s castile soap, and not laundry or dish “soaps,” which are actually detergents that contain perfumes and other ingredients that can damage plants. Soap solutions can burn or even kill plants if they aren’t sufficiently diluted. Include a maximum of 3 tablespoons of soap per gallon of water. You can also purchase a product that’s specifically formulated to kill bugs without burning plants, such as Safer’s Insecticidal Soap concentrate.
Homemade garden sprays that contain hot peppers or aromatic herbs are gratifying to concoct, but they’ll most likely have little effect on insects — it’s the soap typically added to these mixtures that actually works.
No matter which spray you make or choose, bear in mind that if it’s effective on pests, it will also kill beneficial insects and other non-target organisms.