If you’re like many gardeners, you’re not afraid of getting your hands dirty and tackling challenges yourself. So when insects begin eating your plants, you head to your pantry and garden to whip up an all-natural homemade insecticide spray. But do these DIY products even work?
Using plants to create insecticides is a process that goes back hundreds of years. However, in the age of the internet, I’ve seen people claim just about anything will help repel aphids or kill the armyworms that are eating your tomatoes.
That’s why I’m here to help you determine which homemade products you can rely on. Plus, I’ll share some organic insecticides you can purchase if you want to skip doing it yourself.
The Short Answer
Many of these sprays require regular, repeated applications to control pests effectively.
Since there are hundreds of different insect and arachnid pests, and handfuls of different DIY insecticide sprays, there’s no one-size-fits-all answer to whether or not these homemade products work. In short, many of these sprays deter or kill some common garden pests.
These DIY sprays often kill some bugs but not as many as commercially available organic insecticides. The efficacy of these products varies depending on the strength of the solution, the targeted species, and application practices. For example, you can make a garlic spray in hundreds of different ways, so one garlic spray is not necessarily the same as the other!
While the main question is whether or not they control infestations, you should also consider whether homemade insecticide sprays are safe to use and easy to apply. Many of these sprays require regular, repeated applications to control pests effectively. Often, this means spraying once or twice a week.
The Long Answer
The effectiveness depends on the type of spray.
The effectiveness of homemade insecticides depends on the type of spray, the pest at hand, and the application method. I’ll go over a few popular homemade sprays and explore how they impact garden infestations.
Hot Pepper Spray
This unique compound is what makes people interested in using hot peppers as insecticides.
Chili peppers get their heat from the compound capsaicin. A higher amount of capsaicin means a spicier pepper. This unique compound is what makes people interested in using hot peppers as insecticides.
What Science Says
Repeated sprays were more effective than a single treatment.
A 2016 study investigated the impact a hot pepper spray had on four common cabbage pests: the cabbage aphid, diamondback moth larvae, cabbage looper, and cabbage webworm. Researchers waited until the insects were present on the plants before spraying them with the hot pepper solution. By measuring the number of pests on the plants before and after treatment, they were able to determine the spray’s efficacy.
Results showed that the hot pepper spray decreased all three species. However, depending on the insect, the sprays only reduced the pest populations by 18-55%. It’s also important to note that the researchers sprayed the plants each week and collected the data for pest reduction three weeks after spraying.
Results Depend on Dosage
Researchers in another study looked at the effect of natural capsaicinoids (compounds related to capsaicin) in controlling 14 insect pests and compared these natural materials to common commercial pesticides. Results showed that a higher dose of the chili pepper compounds was required to kill the insects than the pesticides, indicating that the capsaicin compounds are less effective.
The results also showed that the capsaicin treatments affected some pests more than others. Plus, they indicated that repeated sprays were more effective than a single treatment.
Hot pepper sprays can control some pests, but they don’t work the same on all insects. Therefore, you have to experiment to see which insects you can control with this DIY spray.
Garlic Spray
When you crush the garlic, a substance called alliin is converted into allicin.
If you have a few extra heads of garlic lying around, you can blend or mash the cloves in water to make a garlic spray. When you crush the garlic, a substance called alliin is converted into allicin. Environmental exposure then causes the allicin to break down into sulfur-containing compounds that help repel and harm pests.
What Science Says
Researchers found that plants sprayed with a weekly 1% garlic solution had higher chlorophyll content and yield.
One study investigated the impact of garlic spray on zucchini pests and overall plant health. Although observing the presence of pests was one part of the study, researchers mainly looked at plant chlorophyll content, fruit yield, and the antioxidant content of the fruit.
Researchers found that plants sprayed with a weekly 1% garlic solution had higher chlorophyll content and yield. They speculated that garlic acted as a biostimulant and improved the plant’s health. The study’s authors proclaimed that the garlic extract had a “repellent and/or preventive effect against insect vectors.”
Results Depend on Concentration
Researchers in another study looked at how garlic sprays affected two insects: the common housefly (Musca domestica) and the cabbage fly (Delia radicum). The results showed that garlic juice could kill the eggs, larvae, and adult forms of these pests, but the efficiency of the garlic depended on the concentration of juice as well as the time the pests were exposed to the juice.
For example, when researchers exposed housefly larvae to a 26.4% garlic juice solution for 24 hours, half of the larvae died. But if they exposed the larvae for 48 hours, a 6.8% solution would kill half of the flies. Overall, a long exposure time or high garlic concentrations improves the efficacy of the spray.
A third group of researchers examined whether or not garlic sprays could be used to control aphids on cotton. The researchers separated cotton plants into five different groups. They sprayed three groups with different strengths of garlic solutions, one group with the synthetic insecticide dimethoate, and left one group untreated. It’s important to note the garlic sprays contained mineral oil and soap as well as garlic.
The results showed that while the control group had about seven aphids per plant 20 weeks after planting, the other four groups had less than one aphid per plant. That suggests garlic spray is an effective way to control cotton aphids.
Researchers in a fourth study examined the impact garlic sprays had on different types of cabbage pests. These researchers looked at the number of pests present on the plant before and after spraying, so the results serve as a good indicator of whether or not garlic spray can control pests once they’re present. The results show that garlic sprays decreased the number of cabbage aphids, diamondback moth larvae, cabbage loopers, and cabbage webworms present on the plants. However, the pest populations decreased by less than 50%.
While spraying with garlic will help manage populations, this treatment is unlikely to kill 100% of the pests. Furthermore, high concentrations of garlic and regular spraying are key to effective control.
Even though garlic sprays are unlikely to solve an infestation, they can help promote plant growth and improve plant defenses. Plus, they’re highly unlikely to hurt your plants. So, if you want to spray your plants with garlic, go for it! Just don’t expect it to be a cure-all.
Neem Spray
All parts of the plant contain compounds that help it fight off diseases and insects.
Neem is a tropical tree native to India and Bangladesh. All parts of the plant contain compounds that help it fight off diseases and pests, but the seeds are particularly rich in the compound azadirachtin. This chemical is known to disrupt reproduction and molting in many insects, and it also prevents some species from feeding on plants.
What Science Says
It’s important to note that neem’s effectiveness quickly diminishes when it is exposed to the sun.
Homemade neem insecticide sprays have been shown to effectively control a range of pests, including true bugs, thrips, and caterpillars. One study examined the impact of neem sprays on common radish pests. Researchers divided radish plants into three groups that received different sprays:
- Water (control group)
- Neem leaf extract
- Neem seed extract
Results Prove Neem is Highly Effective
Both neem sprays resulted in quicker deaths of flea beetles, thrips, and white flies and led to less leaf damage. However, the neem seed spray was the most effective at controlling the insects.
Other studies support the efficacy of neem in killing insect pests and report that it has a recognizable effect on species such as the cotton bollworm, cabbage moth, and fall armyworm. However, it’s important to note that neem’s effectiveness quickly diminishes when it is exposed to the sun. Therefore, repeated applications are often necessary.
Neem sprays are effective and safe ways to control a variety of insect pests. However, since neem isn’t a common plant in the United States, it often makes sense to purchase commercially available neem oil rather than making your own spray. Not only is neem oil easy to find, but commercial products come in known concentrations that make it easy to properly mix and apply neem to your plants.
Marigold Spray
Planting marigolds in your veggie garden can help keep bugs away.
You may have heard that planting marigolds in your veggie garden can help keep bugs away. But can you create an effective insecticide spray from these potent flowers?
What Science Says
Results showed that the marigold extracts interfered with the health of fall armyworm larvae.
While multiple research studies have examined interplanting marigolds with other types of plants, fewer researchers have examined using marigolds as a spray. Still, there is some research we can look at to explore the plant’s effectiveness.
Results Show Low to Moderate Effectiveness
One study examined the impact of marigold (Tagetes spp.) extracts on tarnished plant bugs and whiteflies. While the pests died more quickly when exposed to the marigold extracts, the time to death didn’t correspond with the strength of the solution. Therefore, the researchers were hesitant to say how the extracts impacted the pests.
Researchers in another study examined how extracts from two marigold species impacted pests. Results showed that the marigold extracts interfered with the health of fall armyworm larvae.
Although some research shows that marigold extracts can help control some insect pests, there isn’t much information available regarding how effective these sprays are against other pests. Therefore, you’ll likely need to test these sprays on different pests to determine their efficacy.
Tips for Using Homemade Insecticide Sprays
Before making your own sprays, understand these best practices.
If you want to try making and using your own sprays, it helps to follow a few best practices.
- Add surfactants to sprays: Surfactants are materials that improve the wetting and spreading abilities of liquids. When you add them to homemade insecticides, they increase the solution’s ability to coat plant leaves. Castille soap is a safe surfactant, as opposed to dish soap, which contains compounds that can be harsh for plant tissues.
- Remember that concentration matters: No matter which natural product you’re using to make your insecticide, remember the amount of active ingredient in the spray is important. A spray with a high percentage of the active compound will be more effective than a spray with a low percentage.
- Add oil: While it’s not essential, adding a plant-based oil to your spray can help improve its effectiveness. The oil helps the spray penetrate plant leaves and insect exoskeletons.
- Take notes: When you create and use a new spray in your garden, take notes on how you made it and applied it. Next, keep track of which pests it affected. You can use this information to inform future pest control efforts.
- Use caution: Even insecticides made from natural products can pose harm to organisms and the environment. Avoid spraying the products near beneficial insects, and handle all products with caution.
Consider Commercially Available Products
Many commercially available products are approved for organic production.
Just because you want to avoid synthetic insecticides, it doesn’t mean you have to make products yourself. Many commercially available products are approved for organic production and made from natural ingredients. Look for the label that says OMRI Approved for Organic Production.
Here are some common insecticides that work well on garden pests.
Neem Oil
Many commercially available products are approved for organic production.
As I mentioned above, neem oil is an effective way to control various garden pests. Many commercially available products are approved for organic production, and they make it easy to ensure you’re applying the correct dose of the product.
Bacillus thuringiensis (Bt)
It’s made from a naturally-occurring soil bacteria that stops these caterpillars from feeding.
If you’re dealing with members of the Lepidoptera family, like cabbage worms, armyworms, tomato hornworms, or corn earworms, Bt is a great insecticide to try. It’s made from a naturally-occurring soil bacteria that stops these lepidopterans from feeding. Therefore, it harms caterpillars and worms without affecting other insects.
Insects must eat Bt in order for it to affect them. A light mist should be enough to coat the plant. In many cases, this biological product can be more effective than homemade insecticide sprays.
Pyrethrin Sprays
These compounds impact insects’ nervous systems, leading to death.
Pyrethrins are a group of six compounds derived from chrysanthemum plants. These compounds impact insects’ nervous systems, leading to death. Unlike many organic insecticides, these sprays kill insects within a few hours.
Pyrethrin sprays impact a wide variety of insects, including beneficial ones. Therefore, you should be extra careful when applying these sprays to your plants. A good practice is to spray in the morning or evening when pollinators are least active. Additionally, spray on a calm day to prevent pesticide drift.
