Neem Oil Negatively Affects Beneficial Insects – The Case Against Using Neem in the Home Garden

I see neem oil recommended in gardening circles/groups all the time. It’s the go-to insecticide/pesticide touted for use against aphids, thrips, white flies, mealybugs, rust, powdery mildew, and more.

Derived from the neem tree, neem oil is a naturally-occurring botanical extract. It’s natural! It’s organic! Many studies show that it’s less harmful to the environment and to beneficial insects than conventional pesticides (Adusei & Azupio, 2022; Aziz, Ahmad, Nasir, & Naeem, 2013; Raguraman & Kannan, 2014). And it will put a stop to those pesky aphids (Aziz, Ahmad, Nasir, & Naeem, 2013; Lowery & Isman, 1995). 

It sounds great, right? Not so fast. Let’s examine what we are actually spraying throughout our gardens.

First, it’s good to know that there are two types of neem oil out there. There’s an important distinction between the two that I don’t think many people are aware of.

Cold-pressed neem oil contains the active component azadirachtin, while clarified hydrophobic extract of neem oil has been processed in a way so as to remove the azadirachtin. While the neem oil most commonly sold at garden centers is the extract of neem oil, some of the most popular brands (such as Captain Jacks and Safer) sell both products with hardly any distinction in their labeling. 

While it might not seem like it, the products are completely different in terms of their application and effects on target and non-target organisms (and neither product is harmless for beneficials, as I’ll show below). If you already have a “neem oil” product (or are considering one), I encourage you to take a look at the ingredient list on the label to determine which of these products it is, and read on for a breakdown of each one.

The harmful effects of azadirachtin (cold-pressed neem oil)

The active component in cold-pressed neem oil is azadirachtin, which is a known anti-feedant that deters insects from eating and disrupts their growth and reproduction. It’s not an instant kill, but a slow death over time. It’s most effective on insect larvae and generally works to stop them from successfully becoming adults, thus halting the insect life cycle. Studies have shown that this component is not selective in its effects. Rather, over 500 insect species are affected by its properties (Silva & Martinez, 2004), including the beneficials, at least to some extent. 

Silva and Martinez (2004, p. 753) found 34% more deaths of the larvae of spotless ladybugs that had been sprayed with neem oil at certain concentrations, as compared to the control. Even worse, Khan et. al (2015, p. 145) found 80% mortality of zig zag ladybug eggs treated with neem, while adults only emerged from 13% of pupae that had been sprayed with neem (the remaining 87% died). These do not look like encouraging numbers to me. 

Studies have shown similar negative effects on other beneficial insects such as bees, green lacewings, minute pirate bugs, hoverflies, parasitic wasps, and more (see Ahmad, Oßiewatsch, & Basedow, 2003; Cloyd, 2012; El-Wakeil & Saleh, 2009; Golec, 2007; Kaur, Singh, & Singh, 2022; Martins Filho, Duarte, & Venzon, 2023; Ullah, et al., 2022; Xavier, et al., 2015). 

Even if the beneficials aren’t sprayed directly, eating aphids that had been sprayed with azadirachtin caused harlequin ladybugs to stop eating further aphids, which caused low bodyweight and abnormal development (Qin et al., 2021). Similarly, eating neem-treated aphids led to high mortality rates on the larvae of several beneficial aphid predators (Ahmad, Oßiewatsch, and Basedow, 2003). 

The harmful effects of clarified hydrophobic extract of neem oil

The clarified hydrophobic extract of neem oil is, in my opinion, some very clever marketing. They get to use the word “neem” and all its effective pest-control associations, while they have in fact extracted the very component that makes neem a unique insecticide. 

What you are left with is a horticultural oil that acts to suffocate the insect by clogging the pores and their ability to get oxygen. In order for this type of neem oil to be effective, one has to completely coat the target insect with the spray, and any other insects caught in the crossfire will suffer the same ill effects (Skelly, 2013). 

There are far fewer studies on neem oil extract as there are on neem with azadirachtin. But, Ahmad, Oßiewatsch, and Basedow (2003) did an interesting study comparing three different types of neem oil, and found that the one with very little amounts of azadirachtin had the most devastating effects of the three substances. When this neem oil was sprayed on eggs of the common ladybug and green lacewing, it showed 40.7% and 27.7% reduction in the eggs hatching, respectively, as compared to spraying the eggs with water (p. 460). They also found high mortality rates (as high as 100% !) for the larvae of ladybugs, green lacewings, and marmalade hoverflies that ate neem-treated aphids (Ahmad, Oßiewatsch, and Basedow, 2003). 

To me, it doesn’t seem like this neem oil is any better than the neem oil with azadirachtin. Studies have shown that both types of neem oil are harmful to all sorts of different beneficial insects. 

Conclusions and Alternatives

At the end of the day, nothing in gardening is black and white and we are all trying to do the best we can to grow successful gardens with the information we have. 

I personally feel that the harm from neem oils to beneficial insects that I’ve highlighted in this article is hardly ever talked about. I think people might make different decisions if they knew of these ill effects. 

So, what are the alternatives?

Strategic interplanting and good bugs

I recommend strategic interplanting, and numerous studies support this method (Jankowska, 2007; Lopez and Liburd, 2023; Moshira and Ghada, 2021; Sarker, Rahman, & Das, 2007). Aphids detest aromatic plants such as alliums, garlic, onions, chives, marigolds, and other aromatic herbs, so generously planting those in your planting space should help keep them away. Many of those plants, as well as fast-growing flowers such as sweet alyssum, nasturtiums, and calendula will also encourage beneficial insects to stick around in your garden and reproduce. You can also periodically release beneficial insects such as ladybugs, lacewings, minute pirate bugs, beneficial nematodes, and beneficial mites. These bugs do no harm to your plants, but they and their offspring will help them tremendously by eating up the bad bugs. You can often find them at your local garden center, or there are a few places that will overnight them to you such as NaturesGoodGuys. 

Whole cow’s milk for powdery mildew

Now the clarified hydrophobic extract of neem oil is also marketed as a fungicide, and people often use it to help combat powdery mildew. As an alternative, several studies (Bettiol, 1999; Kamel & Afifi, 2020; Ferrandino & Smith, 2007, and many more) have shown that whole cow's milk is extremely effective at combating this fungal disease. It's best to spray it preventively. Mix 1 part milk with 4 parts water and spray it liberally over the foliage of your susceptible plants. Depending on your risk of powdery mildew, you can do this every 1-2 weeks. 

 

Everyone can make a choice as to the best course of action for their garden.

I’ve personally chosen a path where I want to encourage all sorts of beneficial insects to take haven and reproduce in my garden, and in turn help me fight the bad bugs. Thus, I prefer to avoid spraying any neem oils in my garden. 

References

Adusei, S., & Azupio, S. (2022). Neem: a novel biocide for pest and disease control of plants. Journal of Chemistry, 2022(1), 6778554. https://doi.org/10.1155/2022/6778554

Ahmad, M., Oßiewatsch, H. R., & Basedow, T. (2003). Effects of neem‐treated aphids as food/hosts on their predators and parasitoids. Journal of Applied Entomology, 127(8), 458-464.

Aziz, M. A., Ahmad, M., Nasir, M. F., & Naeem, M. (2013). Efficacy of different neem (Azadirachta indica) products in comparison with imidacloprid against English grain aphid (Sitobion avenae) on wheat. Int. J. Agric. Biol, 15, 279-284.

Bettiol, W. (1999). Effectiveness of cow's milk against zucchini squash powdery mildew (Sphaerotheca fuliginea) in greenhouse conditions. Crop Protection, 18(8), 489-492.

Cloyd, R. A. (2012). Indirect effects of pesticides on natural enemies. In Pesticides—advances in chemical and botanical pesticides. https://www.intechopen.com/chapters/37960 

El-Wakeil, N. E., & Saleh, S. A. (2009). Effects of neem and diatomaceous earth against Myzus persicae and associated predators in addition to indirect effects on artichoke growth and yield parameters. Archives of Phytopathology and Plant Protection, 42(12), 1132-1143. https://www.aensiweb.net/AENSIWEB/rjabs/rjabs/2007/782-789.pdf 

Ferrandino, F. J., & Smith, V. L. (2007). The effect of milk-based foliar sprays on yield components of field pumpkins with powdery mildew. Crop Protection, 26(4), 657-663.

Golec, A. F. C. (2007). Effect of neem (Azadirachta indica A. Juss) insecticides on parasitoids. Revista Peruana de Biología, 14(1), 69-74.

Jankowska, B. (2007). Impact of intercropping white cabbage with Pot Marigold (Calendula officinalis L.) and French Marigold (Tagetes patula nana) on the occurrence of cabbage aphid (Brevicoryne brassicae L.), its parasitoid Diaeretiella rapae M’Intosh and predatory Syrphidae. Aphids and other hemipterous insects, 13, 199-209.

Kamel, S. M., Afifi, M. M. (2020). Controlling cucumber powdery mildew using cow milk and whey under greenhouse conditions. Egyptian Journal of Phytopathology, 48(1), 58-70.

Kaur, G., Singh, R., & Singh, A. (2022). Impact of neem oil on developmental stages of honey bee Apis mellifera L.

Khan, S., Ullah, F., Khan, I., Khan, M. A., Khan, S. Z., Khan, M. A., Khan, I. A., & Iqbal, T. (2015). Toxicity of selected insecticides against the zig zag ladybird beetle Menochilus Sexmaculatus. Journal of Zooological Studies, 3(3), 143-147.

Lopez, M., & Liburd, O. E. (2023). Effects of intercropping marigold, cowpea and an insecticidal soap on whiteflies and aphids in organic squash. Journal of Applied Entomology, 147(7), 452-463.

Lowery, D.T., Isman, M.B. (1995). Toxicity of neem to natural enemies of aphids. Phytoparasitica 23, 297–306. https://doi.org/10.1007/BF02981422 

Martins Filho, S., Duarte, M. L., & Venzon, M. (2023). Survival Analysis of the Green Lacewing, Chrysoperla externa (Hagen) Exposed to Neem-Based Products. Agriculture, 13(2), 292.

Moshira, A. E. S., & Ghada, M. R. (2021). Influence of intercropping onion, garlic and fenugreek with faba bean on yield, and on population densities of aphid and its associated predators.

Qin, D., Liu, B., Zhang, P., Zheng, Q., Luo, P., Ye, C., Zhao, W., & Zhang, Z. (2021). Treating green pea aphids, Myzus persicae, with azadirachtin affects the predatory ability and protective enzyme activity of harlequin ladybirds, Harmonia axyridis. Ecotoxicology and Environmental Safety, 212, 111984. https://doi.org/10.1016/j.ecoenv.2021.111984

Raguraman, S., Kannan, M. (2014). Non-target Effects of Botanicals on Beneficial Arthropods with Special Reference to Azadirachta indica. In: Singh, D. (eds) Advances in Plant Biopesticides. Springer, New Delhi. https://doi.org/10.1007/978-81-322-2006-0_10

Sarker, P. K., Rahman, M. M., & Das, B. C. (2007). Effect of intercropping with mustard with onion and garlic on aphid population and yield. Journal of Bio-science, 15, 35-40.

da Silva, F. A., & Martinez, S. S. (2004). Effect of neem seed oil aqueous solutions on survival and development of the predator Cycloneda sanguinea (L.)(Coleoptera: Coccinellidae). Neotropical Entomology, 33, 751-757.

Skelly, J. (2013). Horticultural Oils: What a Gardener Needs to Know. University of Nevada Cooperative Extension. https://naes.agnt.unr.edu/PMS/Pubs/2021-3029.pdf 

Ullah, M., Ullah, F., Khan, M. A., Ahmad, S., Jamil, M., Sardar, S., Tariq, K., & Ahmed, N. (2022). Efficacy of various natural plant extracts and the synthetic insecticide cypermethrin 25EC against Leucinodes orbonalis and their impact on natural enemies in brinjal crop. International Journal of Tropical Insect Science, 42, 173-182. https://doi.org/10.1007/s42690-021-00528-1

Xavier, V. M., Message, D., Picanço, M. C., Chediak, M., Júnior, P. A. S., Ramos, R. S., & Martins, J. C. (2015). Acute toxicity and sublethal effects of botanical insecticides to honey bees. Journal of Insect Science, 15(1), 137.