Why Does Neem Oil Stop Working On Pests

Latest posts by Ashley (see all)

Have you ever wondered whether or not Neem oil actually works for a plant pesticide? You may have noticed after using neem that the pests still remain. This blog post looks at exactly why neem oil seems to stop working on pests. As well as why neem may not be working for you in your house plant collection.

If you are new to this blog my name is Ashley and I am a soil scientist. I am located in a Canadian Zone 3 and a USDA Zone 4. I write articles, make YouTube videos, Instagram & Facebook posts all designed for Canadians and Cold Climate gardeners using science-based methods. If you are looking for anything specific be sure to let me know in the comments down below.

What is neem oil?

Neem has been made popular as a useful Pesticide. It is commonly touted as the best way to remove common pests both in the garden as well as in the house plant Arenas.

Neem is actually a tree called Azadirachta indica. This broadleaf evergreen tree grows in India, Sri Lanka and Burma. The tree produces nuts which eventually fall to the ground and are pressed to extract the oil. This is very similar to how olive oil is produced.

Click here for a Neem Oil that would actually work due to its processing.

How to choose the best neem oil for plants

The active ingredient in the name is called azadirachtin. This active ingredient in neem oil is what essentially harms the insect. The cold press process is what ensures that the azadirachtin does not degrade. Other ways of processing include clarified hydrophobic name oil, pure, hundred percent natural, extracted and concentrated.

All these descriptors are fancy verbiage & mean nothing. The only thing you need to look for when considering a Neem oil product as a plant pesticide is the cold-pressed process. Cold press processing is the only way to ensure that the active ingredient in the neem oil is still present. Without the presence of the active ingredient, it is essentially no better than just a regular oil product. Neem oil is likely to stop working on pests when it is hydrogenated for example.

Powered by RedCircle

How does neem oil work on adult insects

Neem oil has the ability to coat the leaves making them unpalatable to some insects. This means it does not do harm to the insect per se. This is why it is not uncommon to still see insects on the plant leaves despite the fact that you have applied the neem insecticide. This is because the neem oil does not kill the insect rather it deters the insect from feasting on your plant. 

There are other products out there that are called systemic neem. This means you place it in the soil and it is absorbed by the plant. The thought process is that the plant’s juices (xylem & phloem) will be turned into a neem-type taste. This means the active ingredient that then has a bad taste is present in the leaves. So when a plant pest decides to suck on the juices of the leaf it is deterred by bad taste. 

How does neem oil work on larvae and immature and insects

When it comes to larvae and immature insects neem oil works a little bit differently. The active ingredient in neem oil helps ensure that the insect does not develop properly and eventually dies. This takes time however and starts initially with the larvae stage. The larvae eat the active ingredient in neem which in turn causes the immature insect to fail in full development. 

This process can take a few weeks. This is because the adults are still laying eggs and mating with no repercussions. This again is due to the fact that neem oil does not harm adult insects rather only deters them from eating the leaves. 

Why Does Neem Oil Stop Working On Pests?

The reason why neem does not always work on plants is that insects adapt. The adaptation to neem oil is a little bit different when it comes to insects. Rather than insecticidal resistance, meaning an increased tolerance to an insecticide, we end up with an adaptation to the taste.

As I mentioned before the active ingredient in neem oil makes the taste of the leaves unpalatable for adult insects. But the active ingredient in the neem oil for juvenile insects means that the leaves are semi-poisonous. In the case of adults insects, we are beginning to find some don’t mind the taste. This means they are free to consume the leaves at leisure.

That means for the adult insects that there is a current food source. This food source means that they are able to live and reproduce as they feel necessary. Without a continual application of neem to stunt the larvae and up-and-coming insects we can run into issues. Neem oil is likely to stop working on pests when it is not applied properly & resistance develops.

How to prevent insecticidal resistance with neem?

For ease of reference, we will consider the adaptation to the neem oil taste as insecticidal resistance. When it comes to preventing insecticidal resistance with neem we need to ensure we spray our entire plant population. This means if we suspect an infiltration of harmful insects into our plant collection we want to spray all plants in that area.

This will help ensure that any larvae that are on their way to adulthood will be stunted by that initial neem dosed. Before application to all the plants will also ensure that the adult pests do not have a chance to obtain food from a different plant. These lessons are a chance of adaptation and getting used to the taste of neem.

How is neem applied to plants?

Foliar application of neem oil for plants

The most common way to apply neem oil to your plant is via a spray. This means that it is sprayed on the leaves and stems of the plant. However, through research, we’ve understood the fact that the active ingredient in neem is a large molecule. 

We’ve spoken about molecule size when it comes to foliar spray is in a separate YouTube video. When we looked at foliar sprays we had to understand the fact that not all molecules could break the leaf barrier. This means any molecule that is larger than the stomata can not be absorbed by the leaf itself. 

This is an issue when it comes to your name because we are relying on the flavour of the leaf to change to an unpalatable form. If the name cannot be absorbed into the stomata and therefore the liquid of the leaf we need the outer coating of a leaf to change. This means the name has to be applied on a regular basis if applied regularly to ensure that the taste of the leaf is unpalatable to the insect.

This sounds good in theory however the issue is again that the neem is photosensitive. This means in the presence of sunlight the active ingredient begins to degrade. This obviously will not work because the leaves are in sunlight.

Foliar application of neem oil is likely to stop working on pests when it is not reapplied.

Applying neem to soil

When you apply neem to the soil we actually have better results. This results in a systemic effect because the ability for the neem to be taken out through the roots is high. Because the neem is essentially a product that works on taste rather than sterilization it is completely safe to use in soil.

I rarely advocate for using any sort of pesticide within the soil system. This is mostly because pesticides in any form will harm the microbial activity within as well. Whenever we harm the microbial activity we are essentially harming natural processes such as nutrient cycling. Neem unfortunately is not biased towards only harmful pests. It has been discovered that it has a kill range of around 200 different types of insects. Some of these insects do include beneficial insects that help with the decomposition process within your soil system. 

When we add it to the soil it is uptaken by the roots and therefore it is changing the taste of the plant sap. This happens because the neem oil is officially inside the plant and a part of the xylem or phloem.

One thing to keep in mind is that alkaline soils have poor absorption when it comes to neem oil. This means alkaline soil or anything above a seven pH has a lower ability to absorb nutrients into the plant.

Neem oil for plants in Canada? Why Does Neem Oil Stop Working On Pests When It Is Homemade

Unfortunately for Canadians name is not a registered pesticide and therefore you cannot buy it as such. This likely is due to the fact that it doesn’t have a lot of place in scientific literature and therefore Agriculture Canada is not jumping at the opportunity to approve it.

There are plenty of Canadian forums out there explaining to Canadian houseplants people and Canadian gardeners alike that you can purchase neem from a Swadesh market. Unfortunately, neem tree leaves, bark, oil that is not cold pressed do not have the much-needed active ingredient present. This means it is not going to work as a systemic or a foliar form of pesticide.

As a Canadian, I heavily suggest you go for a more biological control method. There are plenty of biological control companies in Canada and I’ve done several blog posts, podcasts and YouTube videos about these products. This will allow you to maintain a healthy ecosystem both indoors and out without the use of both organic or inorganic pesticides. 

Trust me when I say this using a biological form of control is going to be in your favour. You will notice that pest control is much easier and efficient under these conditions. 

There you have a complete guide to using Nimoy oil with your house plants or in your garden. I hope this helped you understand a little bit more about why name oil doesn’t always seem to work in all cases. Let me know if you knew this information before I would love to know if my blog or YouTube videos help you learn something new.

Why Neem Oil Stops Working on Pests
Why Neem Oil Stops Working on Pests