6 Natural Pesticides for the Garden + How to Protect the Good Bugs While Controlling Pests
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If you’re interested in growing organically, I’d bet a big part of the reason is because you’re informed about the health and environmental hazards that come along with conventional pesticides. They’re toxic to pets and animals, and they can cause cancer, birth defects, and other health problems in humans. Obviously, we’d rather not put them on our food or spray them in our yards.
For dealing with insect pests, organic gardeners can pick from a selection of natural pesticides that are approved for use in USDA-certified organic food production. OMRI-listed pesticides, such as neem oil and Spinosad, are developed from only natural ingredients. They won’t contaminate the environment, and they’re non-toxic enough you can apply them right up until the day of harvest.
Sounds good, but here’s the catch:
Since they’re marketed as being so natural and harmless, people tend to assume products like these can be used without any consequences. And while it’s true they’re a lot safer for us, they can cause serious problems for pollinators and beneficial insects when they’re applied carelessly. For that reason, it’s important to understand how these products work, how they affect different insects, and what risks they pose to beneficial species.
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The Importance of Protecting Beneficial Insects
This matters in both the big picture and the small picture. As we’re all pretty much aware at this point, the decline of pollinators is a big deal on a global scale, since their disappearance would threaten our food security. But it matters for your little garden plot in the short term, too.
While organic-approved pesticides may be natural, the way we use them isn’t natural for the ecosystem. They can disrupt beneficial species and upset the balance of things in your garden, which will set you up for even more pest pressure.
Pest insects tend to reproduce prolifically compared to other species. Trust me, you’ll never get them all, so you want their natural predators around to help keep them under control. You definitely don’t want to douse your garden in something that will knock down your spider population!
Natural Pesticide Options and Risks
First, let’s look at the basics of six common natural pesticide products, plus their potential risks to beneficial wildlife:
1. Neem Oil
Neem oil is the OG of organic garden pesticides, since it’s been used for that purpose for thousands of years. It’s an oil pressed from the seed of the neem tree, and it’s most often found in a pure oil form or a concentrate form. I’d say everyone who’s dipped a single toe into organic gardening has heard of neem oil!
How it Works: The strong, garlicky scent of neem oil alone deters some pests. But more importantly, it contains a compound called Azadirachtin, which is toxic to the nervous system of many pest insects. When they ingest it, it kills their appetite and also interferes with their growth and their ability to mate and lay eggs.
Neem can work immediately against soft-bodied insects such as aphids and whiteflies, since the oil suffocates them, and it will control other leaf-eating pests over time. It’s also believed to help prevent fungal diseases in plants.
How to Use It: Mix neem oil concentrate in a sprayer with water (usually 1 to 2 Tbsp. per gallon) and spray on plant foliage. Depending on your product, you may want to add an emulsifier (~ 1 tsp. liquid soap) to help the oil stick.
Risks to Pollinators and Beneficials: Medium
There’s an ongoing belief that neem is safe for bees, since they don’t eat leaves and therefore won’t ingest it. However, we now have evidence they can be exposed via pollen. Foraging bees may then take the toxin back to the queen and harm the entire hive. For that reason, it’s best to avoid using neem oil on plants that are flowering.
2. Pyrethrin
Pyrethrin (also known by the alias pyrethrum) is a naturally occurring chemical extracted from chrysanthemum flowers. Though it was first registered as a pesticide in the mid-1900s, it’s been used for its insecticidal properties since well before then.
How it Works: A broad-spectrum insecticide, pyrethrin targets the nervous system of most insects on contact, quickly causing paralysis and death. It’s more effective against the larger pests that aren’t bothered by other organic pesticides, such as stink bugs, leaf-footed bugs, and beetles. It will also help with managing aphids, caterpillars, leafhoppers, mealybugs, thrips, whiteflies, and mites.
How to Use It: You’ll find pyrethrin in both liquid concentrates you can mix with water or in ready-to-use sprays. Pyrethrin must be sprayed directly on pests while they’re present and active. Once it’s dry, it won’t work.
Risks to Pollinators and Beneficials: High
Pyrethrin loses its effectiveness quickly as it begins to dry, so it’s low-risk for pollinators as long as it isn’t applied while they’re active. But the fact that it’s such a broad-spectrum and highly potent toxin makes it a big threat for other beneficial insects and critters that may make their homes in your garden plants. While a lot of natural pesticides work through ingestion or by coating soft-bodied pests, pyrethrin kills just about everything on contact. That means your beneficials only have to be in the wrong place at the wrong time.
3. Spinosad
A bio-insecticide, Spinosad is derived from the soil-dwelling bacterium S. Spinosa.
How it Works: Spinosad acts as a nervous system toxin in insects, causing paralysis and death in a large range of pest species. It works best when ingested by leaf-chewing pests, but it also has some effect on contact while it’s wet. Unlike pyrethrin, it can keep working on plant foliage for weeks instead of hours.
Spinosad will control leaf miners, thrips, caterpillars, and many kinds of beetles. It’s especially effective for beetles whose larvae feed on leaves (like the Colorado potato beetle) since the larvae are most susceptible. Once they’ve ingested Spinosad, pest insects die within a day or two. Note that it won’t control “true bugs” such as stink bugs and leaf-footed bugs.
How to Use It: Spinosad can be found in a liquid concentrate, a pre-mixed spray, and sometimes a powder, but the liquid concentrate kind is most common. You’ll mix the product with water in a sprayer per the instructed ratio and spray it on plant foliage.
Risks to Pollinators and Beneficials: High
Spinosad is considered safe for pollinators, if applied when they aren’t active. It was thought to spare other beneficials, too, but new studies show it’s highly toxic to spiders when they come in contact with it. Even if it doesn’t outright kill them, it causes crippling neurological damage. Spiders exposed to Spinosad have trouble building webs, hunting for food, and mating. Spinosad can also harm earthworms if a lot of it soaks into the soil.
4. Bacillus Thuringiensis (Bt)
Bacillus thuringiensis is a bacterium that’s toxic to the larvae of specific insect pests. While there are several different strains of Bt used to control different insect larvae, the one most used in home gardens is the Btk (Bacillus thuringiensis kurstaki) strain, which targets the caterpillars of butterflies and moths.
How It Works: When a caterpillar ingests Bt, the bacteria produces toxins that bind to the gut wall, causing the caterpillar to lose its appetite. Caterpillars poisoned with Bt will stop eating within minutes. Bt controls cabbage worms, cabbage loopers, armyworms, corn earworms, and tomato hornworms, just to name a few.
How to Use It: You can buy Bt in a liquid concentrate for mixing, a ready-to-use spray, or a powder such as Dipel Dust. Dipel Dust works best for brassicas like cabbage and broccoli, since it’s hard to get liquid sprays to stick to their waxy, water-resistant leaves.
Bt should be dusted or sprayed on affected plant foliage in the evening, since high heat can make it less effective. It washes off easily in rain and breaks down quickly after spraying/dusting, so you may need to reapply multiple times to control a caterpillar problem.
Risk to Pollinators and Beneficials: Low, when used appropriately
Bt is non-toxic to bees, but as with any pesticide, it should never be sprayed while they’re foraging. It is also non-toxic to most other beneficials, like spiders, lightening bugs, ladybugs, etc. This is why I prefer using Bt for caterpillar problems over a broad-spectrum option like Spinosad. I like to use a Bt concentrate like this one; you only need a tablespoon or so per gallon of water, so one bottle will last for several seasons.
The one danger with using Bt is that it will target butterfly caterpillars as well as pest caterpillars. Never apply Bt on or even anywhere near host plants of local butterflies. Several host plants that might be in your garden are all varieties of milkweed (monarch host plant) and plants in the carrot family (black swallowtail host plant). Those include dill, fennel, parsley, and of course carrots. Bt is not dangerous for adult butterflies and moths- only caterpillars.
5. Insecticidal Soap
Insecticidal soap is made of the same compound as any soap- a strong alkaline substance and a fat. Commercial products usually contain potassium salts and fatty acids.
How It Works: Insecticidal soap stops pest insects via suffocation. It can also disrupt cellular membranes and strip away the protective waxes insects have, which causes them to dry out. The soap works best for those small, slow-moving, squishy pests- aphids, thrips, mealybugs, scale insects, and mites. It doesn’t work against their eggs.
How to Use It: To apply insecticidal soap, you’ll normally dilute it with water (amount will depend on your product) and spray it directly on plant foliage. There are also some ready-to use sprays available.
Be aware that insecticidal soap sprayed during hot, sunny weather may burn plant leaves. Some plants are just overall sensitive to it and may not react well. Examples include nasturtiums, azaleas, geraniums, and impatiens. That’s not an exhaustive list, so always do some quick research before you spray.
Risk to Pollinators and Beneficials: Low, if used appropriately
Insecticidal soap must coat target insects in order to kill them, meaning it won’t affect bees and pollinators as long as you spray in the evening when they’re not out foraging. Since the soap mainly targets tiny pest species, other beneficials such as spiders and predatory insects aren’t likely to be harmed by it.
6. Diatomaceous Earth
Sometimes just called DE (for obvious reasons!), diatomaceous earth is made from the fossilized remains of diatoms, a type of algae whose skeletons are high in silica. DE is mined from deposits formed by the fossilized algae and ground into a fine powder for different uses.
How it Works: To us, DE feels soft as flour, but it’s full of tiny sharp particles that damage the exoskeletons of insects when they come in contact with it. It also sticks to them and absorbs all the moisture from their bodies, drying them out. DE will work most quickly on soft-bodied insects, but it’ll take down anything with an exoskeleton, in time. It’s highly effective against snails and slugs, since they depend on moisture for survival.
How to Use It: In the garden, DE can be dusted on plant foliage or placed around plants as a barrier to prevent pests such as slugs and cutworms from damaging them. DE only works when it’s dry, so it must be reapplied after rain. Though it’s non-toxic, dry DE can cause serious irritation if you breath it in or get it in your eyes. Use caution and wear a dust mask and safety glasses when you’re handling it.
*Note that there are two kinds of DE: food grade and pool grade. Always use food grade for the garden. Pool grade DE is meant for use in swimming pool filters, and it’s pretty caustic and not safe to handle.
Risks to Pollinators and Beneficials: Medium
In this case, the risk level really depends on how you apply DE. When it’s dusted on an entire plant, any insect that crawls on the foliage will be affected, pests and beneficials alike. It can also harm bees if it gets on flowers. DE is safer for beneficials when it’s used as a barrier around the base of plants. Since it’s contained to a small area on the ground, they’re less likely to come in contact with it.
Controlling Bad Bugs Without Pesticides
As a regenerative gardener, I firmly believe pesticides, even the natural ones, should be a last resort. We can be proactive and use a combination of non-chemical methods to keep pests down. This is called integrated pest management, and it can really cut down on the need for pesticides. Here are some ways you can practice it:
-Focus on plant health, first. Malnourished or stressed plants are both more likely to become targets of pests and more sensitive to the damage. Make sure your plants are properly watered and fertilized as needed.
-Use companion plants like flowers and herbs to diversify your garden and attract more natural pest predators.
-Hand pick your bugs. Lots of large, easy-to-spot pests like caterpillars, beetles, and slugs can be controlled effectively by scouting and removing any you find. Sometimes, hand-picking actually works better than some of the products mentioned above for these types of pests.
-Set up some insect netting for pest-prone crops. Insect netting keeps many types of pests out proactively, reducing the need for pesticide sprays (and your workload).
Read this post to learn more about alternatives to sprays and dusts for controlling pests: Eco-Friendly Garden Pest Control: 6 Ways to Reduce Pest Damage Without Spraying.
When Should You Consider Using Natural Pesticides?
Noticing pest damage on your plants doesn’t automatically mean you need to take action. Here are a few things to consider, first:
-Pest insects are part of the little ecosystem in a garden. They provide food for beneficials, birds, and other wildlife. I don’t start thinking about an intervention until I see significant pest damage happening to plants, such as holes in multiple fruits, lots of dying leaves, skeletonized branches, etc.
-Plants, especially healthy ones, can handle some pest pressure without negative effects. Holes in leaves from leaf-chewing insects are often just cosmetic, especially for plants you harvest fruit from instead of greens. ID the pests and observe what kind of damage they cause before you start worrying.
Small populations of flea beetles and aphids won’t cause much of a problem for healthy plants. Also, my pole beans can take an absolute beating from Mexican bean beetles and still continue producing well into fall. I hand pick the beetles when I see them, but I don’t spray.
-Know your pest insects and their habits to decide whether using a pesticide is the most practical option. For example, the squash vine borer caterpillar isn’t easy to control with pesticides, since they burrow directly into the vines where they won’t be exposed. I’ve found that weekly preventative Bt sprays will only save a few of my plants (if I’m lucky), so it isn’t worth the effort. Sometimes, passive methods like row cover for young plants just make more sense.
Other pests are simply easier to deal with manually. Tomato hornworms don’t usually come in droves, since the adult moth only lays a single egg here and there. You’ll rarely find more than a few at a time. To me, checking for them every few days and hand-picking them is less fuss than mixing enough Bt solution to spray 20 large tomato plants.
-Consider the size and health of the plant. Seedlings experiencing transplant shock are much more likely to be killed or set back by pests. While I’ve had struggling seedlings overcome a thrip infestation with some liquid fertilizer and extra TLC, slugs and pest caterpillars can make short work of them.
Reducing the Ecosystem Impacts of Natural Pesticides
If you end up needing to treat your plants with a natural pesticide, here are some ways you can protect your beneficial insects in the process:
-Never spray or dust anything when pollinators are active, during the daytime hours. Only spray later in the evening or early in the morning. This is the golden rule that applies to any pesticide you might use.
-Look closely at your plants and pinpoint where beneficial insects are present. If you don’t see the insects themselves, look for signs like spider webs. This way, you can avoid treating areas where they’ve set up shop.
-When possible, avoid using broad-spectrum pesticides and opt for targeted ones instead. For example, opt for Bt instead of Spinosad to deal with a caterpillar infestation, since Bt only affects caterpillars. For tiny pests like aphids and thrips, something like pyrethrin is way over-kill. Use some insecticidal soap, since it’s non-toxic to beneficials.
-Spot-treat affected plants/areas rather than spraying or dusting widely, especially if you’re using a broad-spectrum pesticide. For some reason, the slugs at my place like to eat seedlings in one specific bed, no matter what is planted in it. I’ll find major munching in that bed, and only a small nibble or two in others. If slug damage is high, I might sprinkle DE around the base of seedlings in their preferred feasting grounds, but there’s no reason to treat my other beds if the slugs aren’t bothering them much.
-Don’t spray or dust blooming plants with anything that can have a residual effect, like neem, Spinosad, or DE, since these pesticides can injure or kill pollinators who visit the flowers. If you need to treat seedlings, you can always pinch off any flowers, first. The plants aren’t big enough to support fruit at that point, anyway.
-Don’t spray or dust more than what is necessary to cover the plant, since too much overspray can soak into the soil and affect earthworms.
Sometimes, a natural pest control spray may be necessary to secure a good harvest. You’ll have to make decisions with that in mind, especially if your goal is to feed yourself and your family with your garden. But using some discretion and mixing up your strategy is the best way protect your garden’s little ecosystem and keep things sustainable.
