8 Organic Pesticides for an Environmentally-Friendly Garden

Do you have pests and want to use an organic pesticide? As a gardener, it's important to keep pests and diseases under control to ensure a healthy and productive vegetable garden. While synthetic pesticides can be effective in controlling pests, they can also have negative impacts on the environment and on beneficial insects.

Fortunately, there are several organic pesticides that can be used to control pests in the vegetable garden. Although even with organic pesticides, there are certain precautions you need to take. Here are 8 organic pesticides that you can use to keep your vegetable garden pest-free:

1. Neem oil

Neem oil is a natural pesticide that is derived from the neem tree. It can repel insects, stop them from feeding, or regulate their growth, depending on the formulation used and the particular insect. They work best on soft-bodied insects (aphids, mealybugs, scale nymphs, spider mites, and whiteflies). It is also effective for fungal diseases, such as foliar diseases, powdery mildew, and rust.

The active ingredient is azadirachtin, although not all neem oil contains a lot of this active ingredient and may be more similar to insecticidal soap. You need to cover the insects thoroughly to be effective. More concentrated azadirachtin is also effective on caterpillars, sawflies, flea beetles, leafhoppers, leafminers, and weevils.

2. Horticultural Oil

Horticultural oils are highly refined, lightweight oils. They are mixed with water and sprayed as a fine mist onto the plant leaves or bark. They work by smothering the insects by covering their spiracles where they breathe. They control soft-bodied insects, especially nymphs. They are not as effective on the adult insects that are protected by a waxy covering (e.g. scale insects).

There needs to be thorough coverage of the underside of the leaves where the insects live. If it is applied as a dormant oil on the bark, a higher concentration of oil is used to control mites or insects that may be overwintering.

Avoid using the horticultural oil when the temperature is 90F or more. They can burn the leaves causing them to fall off.

3. Insecticidal Soap

The active ingredient of insecticidal soap will say potassium salts of fatty acids on the bottle. They work by dissolving the exoskeletons of pests, causing them to dehydrate and die. It is effective on aphids, soft scales, psyllids, whiteflies, mealybugs, thrips, and spider mites. They must be applied directly to work. If your plant has hairy leaves or is suffering from drought stress, it may be more sensitive to it.

Similar to oils, you don’t want to apply this pesticide when the temperatures are high. Wait until the evening when it has cooled down. I was doing an experiment once and I ask my assistant to spray the plant with insecticidal soap and wait until late in the day. He sprayed it at 3:30pm in July. The next day, I didn’t have to worry about the aphids on the leaves of my bean plants because I had no leaves left.

As a DIY solution, you can make your own soap recipe by mixing 1 tablespoon of soap (like castile soap) to every quart of water. Don't use a detergent soap that has additives and fragrances.

4. Pyrethrum/Pyrethrins

Pyrethrins is extracted from the African daisy-like flower Chrysanthemum cinerariaefolium. The powder-form is pyrethrum. Pyrethrins offer quick knock-down of pests such as beetles, stink bugs, aphids, and caterpillars. They affect the nervous system of the insects, causing death. Many formulations contain a booster (i.e. synergist) called piperonyl butoxide which increases the effectiveness of the pesticide.

These are different than pyrethroids which are long-lasting synthetic insecticides that work the same but harm beneficial insects. Pyrethrins on the other hand break down quickly in the environmental, although you should be careful around water bodies since they are toxic to fish.

I always recommend having this one on hand if you do trap cropping with sunflowers. You plant mammoth sunflowers around your garden which attract stink bugs and leaf-footed bugs. You use pyrethrin to kill the stink bugs before they reach your vegetables. This pesticide is also toxic to bees so if you do this method, make sure you do it after the bees have gone back in their hives.

5. Diatomaceous Earth

Diatomaceous earth is made from the fossilized remains of tiny aquatic organisms. It works by scratching the exoskeletons of pests, causing them to dehydrate and die. It works well on indoor pests like ants, fleas, bed bugs, and cockroaches, but also organisms like snails, slugs, cutworms, and earwigs.

Since the compound must be dry to work, it may not be as effective in outdoor situations. The best way to use it is to apply it after the water has dried on the soil during the day. You can apply it around the base of the plant or on the leaves. You will have to reapply it if it gets wet. Reducing overhead watering can help the compound last longer if you apply it to the leaves.

6. Iron Phosphate

If slugs or snails are your problem and wet soils make diatomaceous earth an unsuitable option, iron phosphate may be a better option. It is safter than metaldehyde baits which are highly toxic to pets and wildlife. Iron phosphate works by causing the snails and slugs to stop feeding after ingesting the compound, eventually dying. Brands include Monterey Sluggo and Sluggo Maxx.

Irrigate the area first then sprinkle the bait in the late afternoon or evening. Snails and slugs are most active on cloudy days or at night. Avoid watering afterwards.

7. Bacillus thuringiensis (Bt)

Bacillus thuringiensis is a naturally-occurring soil bacterium that produces a toxin that is harmful to certain insects; it is also known as Bt. It works by targeting the specific pests' digestive system, causing paralysis and death. Bt can be used to control a wide range of pests, particularly caterpillars and other lepidopteran insects.

Bacillus thuringiensis var. kurstaki is toxic to caterpillars, but not adult moths while B. thurigiensis ssp. Israelensis is effective on mosquitoes, black flies, and fungus gnats.

Bt is available in different formulations, such as granules, dust, and liquid, it can be applied to the foliage, soil or used as seed treatment. It is important to note that Bt is a selective pesticide and it targets specific pests, it will not harm beneficial insects, pollinators, and other non-target organisms.

8. Spinosad

Spinosad is a microbial pesticide that is made from a naturally-occurring soil bacteria. It works by attacking the nervous system of pests, causing paralysis and death. Spinosad can be used to control a wide range of pests, including caterpillars, leafminers, flies, thrips, beetles, and spider mites.

It is highly toxic to bees when the spray is wet, but not when it is dry. Applications should be make in the early morning or evening when the pollinators are not foraging. I’ll often see formulations of Spinosad mixed with insecticidal soap.

It's important to remember that these organic pesticides should be used as a last resort, after all other management techniques have been exhausted. It's also crucial to follow the label instructions and use them in accordance with their intended use. Additionally, using organic pesticides will not control all pests, so it is best to use a combination of different management techniques, such as companion planting and crop rotation, to achieve the best results.

In conclusion, there are many organic pesticides available that can be used to control pests in your vegetable garden. By using a combination of different management techniques, such as crop rotation, companion planting and organic pesticides like Neem oil, Horticultural oils, Insecticidal soaps, Pyrethrin, Diatomaceous earth, Iron phosphate, Bt, and Spinosad, you can protect your vegetable garden and enjoy a healthy and bountiful harvest.

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