Created from Indian lilac (Azadirachta indica) seeds, neem oil has earned a reputation as one of the toughest natural remedies against common plant pests available.
Even its byproduct, neem cakes, are valued for providing a combination of nutrients and systemic insecticide.
But when your plants become infested with aphids, it can become a battle against multiple foes, as aphid honeydew attracts ants and can result in sooty mold.
Just how effective is neem oil in fighting a war on so many fronts?
How To Use Neem Oil To Kill Aphids
The good news is, neem oil can kill not only aphids but also ants and even sooty mold.
Using a combination of soil soak and foliar spray can get rid of aphids and help prevent another one in the future.
How Neem Oil For Aphids Soil Soaks Work
A soil soak is made using raw neem oil.
This form of neem oil isn’t as processed as the clarified hydrophobic neem oil found in premade foliar sprays.
As a result, it contains high Azadirachtin levels, a chemical that closely resembles the hormones in many insects.
Ingestion disrupts aphid eating habits and can interfere with growth stages and egg-laying.
Soil soaks work best on larger outdoor plants that are difficult to spray and can last up to 22 days before needing another application.
The plants will soak up the neem mixture, allowing it to act as a systemic pesticide and poisoning any pest that tries to pierce its surface.
As a result, aphid infestations are poisoned without causing any harm to pollinators or other beneficial insects that make contact with the plant.
Making a Neem Oil Soil Soak
Because oil and water won’t mix on their own, you’ll need to use either castile soap or Dawn liquid dish detergent to act as an emulsifier.
- Mix one teaspoon of the soap into a gallon of water and gently stir until it’s mixed well.
- Next, add two tablespoons of 100% percent cold-pressed neem oil to the water.
- To apply, pour a fair amount of the soak onto the soil around the target plant, covering a wide enough radius to feed most of the roots.
- For the average indoor/outdoor plant, this will usually be 2 to 4 cups. More is required for trees and larger shrubs.
- Be sure to use the soak on a day when there’s no rain so the neem won’t be dispersed before being absorbed.
- Repeat every three weeks as a preventative.
Related: How To Apply Neem Oil To Soil
How Neem Foliar Sprays Work
Commercial foliar oil sprays usually contain clarified hydrophobic neem oil, which is a processed form that has most of the Azadirachtin removed
This form of neem oil is still quite potent and will kill aphids on contact by clogging their breathing holes and causing them to suffocate.
The advantage of using foliar sprays is their ability in the control of aphids used as spot treatments on indoor plants, as well as the fast dissipation rate.
A neem spray will generally evaporate with no residue in around 45 minutes to an hour, rendering plant surfaces safe for beneficial insects or pet contact.
Making a Neem Foliar Spray
Neem foliar sprays are widely available, and many brands use safe ingredients, such as Safer Brand BioNEEM.
However, making your own organic insecticide spray is relatively easy and generally has a shelf life of about four days.
Organic Insecticide Spray Recipe
- Gently mix ⅓ teaspoon of Dawn liquid dish detergent or insecticidal soap per quart of water to serve as an emulsifier. Insecticidal soaps leave no residue, so it’s safe for use on both indoor and outdoor plants.
- Add in 1 teaspoon of .5 to 2% percent neem oil (this is often listed as clarified neem oil at garden shops) and pour into your sprayer or a spray bottle.
- Spray the entire plant at either dawn or dusk so it will have dissipated before any pollinators arrive.
- Be sure to soak the plant leaves thoroughly, especially the leaves’ undersides and any joints or crevasses.
When using neem oil on roses or other flowering plants, try to avoid spraying the flowers themselves, primarily if you use insecticidal soaps in your mixture.
Reapply the foliar spray every other day for about 14 days to ensure no aphids or plant bugs survive.
Using the Neem One-Two Combo
Hanging out on the undersides of leaves Aphids often enjoy the company of ants and sooty mold, two tough opponents.
Ants prevent beneficial insects from killing the aphids, while the sooty mold can cause additional destruction to your already suffering plant.
Thankfully, a combo treatment works well on plants that may be too large for a foliar spray alone.
Use a neem soak on the infested plant’s roots and use the foliar spray to get at any pests you can find.
The spot treatment will not only affect aphid populations, but it will poison any ants present and kill sooty mold on contact.
Best of all, research suggests that as much as 20% percent of ingested Azadirachtin remains in an insect’s system, meaning any ants feeding off the honeydew are likely to take some of this natural insecticide back to the colony and spread it around.
Reapply the foliar spot treatment as needed while the neem soak targets the aphids more directly.
While not toxic to humans or pets, it’s best not to apply a neem foliar spray on plants on the day of harvest. Do not use root soaks within three weeks of harvest.
You should also always test neem oil on a small part of the plant first to ensure there are no adverse reactions and avoid treating saplings that may be too sensitive.
Neem oil also used to control powdery mildew.