Why I say NO to systemic pesticides

In my post on Physan 20 I gave my honest assessment of a product that, when used correctly and with appropriate precautions, has legitimate applications such as surface disinfection or tool sterilisation there are contexts to where it earns its place. I was not gentle about its preventive use on living substrates, but I acknowledged the use cases where it makes sense.

I debated with myself whether to write it at all. Not because I am uncertain about the evidence, the evidence is what it is, but because I know what happens when you tell a community that something they rely on, something that genuinely works, something that has become embedded in the standard advice passed between growers, is a problem. People do not like it.

But if this blog cannot give an honest opinion backed by evidence then that is not a me problem. So let us talk about systemic pesticides, why they work so well, what is actually in them, and why I think their indoor household use deserves a worldwide ban.

Before I go further  I want to be clear about what I am not saying. I am not against pest control. I understand that for many growers, particularly those dealing with serious infestations and limited time and space, systemic pesticides feel like the only reliable solution. I am not here to judge that choice. What I am saying is that the risk profile of these products in an indoor household context has not been honestly communicated, and that effective alternatives exist. With patience, they work just as well.

Why They Work So Well

Systemic pesticides are not contact insecticides. They do not sit on the surface of the leaf waiting for a pest to touch them. They are absorbed through the roots or leaves, transported through the vascular system of the plant, and distributed into every tissue the stems, the leaves, the new growth, the roots, the sap.

This is why they are so spectacularly effective. A spider mite feeding on a treated leaf ingests the compound. A thrips on new growth. A fungus gnat larva contacting it through root tissue. There is no hiding, no avoiding treated surfaces, no timing a spray wrong. The entire plant is lethal to anything that feeds on it for weeks or months after a single application.

That effectiveness is also why nobody questions them. A product that needs constant reapplication invites scrutiny. A product that eliminates your pest problem within a week gets recommended everywhere and the question of what else it might be doing never gets asked. Effectiveness silences doubt.

The Question Nobody Asks

Here is the question the hobby does not ask: if this is effective enough to kill insects through the tissues of a plant, what is it doing to everything else in the room?

When you apply a systemic pesticide to a plant pot indoors, you are not applying it in an open field where wind, rain, sunlight, and soil microbiology can disperse it on an agricultural scale. You are applying it in a closed room with limited air exchange, to soil that will get onto your skin by repotting, on a surface that sheds dust particles continuously either through watering or aeration. These compounds do not simply break down. They migrate. From substrate into dust, from dust onto surfaces, from surfaces onto skin. Neonicotinoids can persist in soil for months to years, and in indoor environments where UV degradation is minimal and microbial activity is limited (thanks to Physan 20) that persistence sits at the longer end of any estimate. What you applied to a plant pot six months ago might still be in the room. On your surfaces, in the air, and on the skin of anyone who lives there including pets and children.

The safety assessment that determined these products are acceptable for use was not conducted for someone applying them regularly in an apartment. It was conducted for agricultural outdoor use at defined application rates with assumed dilution and degradation pathways that simply do not exist in your living room. And even that assessment covers only the active ingredient. Not the carrier. Not the adjuvants. Not the full formulation you are applying. In some products the active ingredient makes up as little as 1% of what is in the bottle. The other 99% has largely never been assessed for safety as a mixture. The risk assessment and your actual exposure context are not the same thing.

What else?

The most widely used systemic insecticides in household plant products are neonicotinoids imidacloprid, thiamethoxam, clothianidin, and acetamiprid. Imidacloprid alone has been the most widely used insecticide in the world since 1999.

Neonicotinoids work by irreversibly binding to nicotinic acetylcholine receptors the nerve receptors responsible for transmitting signals across synapses. In insects, this causes overstimulation of the nervous system followed by paralysis and death. The same receptor type exists in the human nervous system. The industry's safety argument is that neonicotinoids bind with much lower affinity to mammalian receptors than insect ones and in acute high-dose exposure, this is broadly true.

The problem is chronic low-level exposure, which is precisely what indoor application creates. A breakdown product of imidacloprid called desnitro-imidacloprid has high affinity for mammalian nicotinic receptors and is highly toxic in animal studies. These receptors are critical to human brain function, particularly during development, and to memory, cognition, and behaviour. The documented concerns from the peer-reviewed literature include neurological toxicity, endocrine disruption, reproductive effects, immunosuppression, and potential contributions to neurodevelopmental disorders. A nationally representative survey of the US general population between 2015 and 2016 found that nearly half of all participants tested positive for neonicotinoid metabolites in their urine people who did not necessarily use these products themselves, exposed through food, water, dust, and air. People who apply them in their homes are adding to an exposure that already exists.

Beyond the active ingredient, some pesticide formulations contain PFAS — per- and polyfluoroalkyl substances, the forever chemicals you know from the water contamination stories and the film Dark Waters. Researchers who specifically went looking for PFAS in pesticide formulations found them present in products that list nothing of the kind on their labels. PFAS do not degrade in the environment or in the body. They accumulate. They have been linked to reproductive toxicity, thyroid disruption, immune suppression, and cancer.

The adjuvant problem goes further. A surfactant called APNOHO — ω-hydroxypoly(oxyethylene) was identified as the single most widely applied pesticide chemical by acreage in California's detailed pesticide reporting system, applied in over 150 adjuvant products. It is associated with endocrine disruption, birth defects, and aquatic toxicity. It does not appear on labels.

Researchers have called for mandatory disclosure of all inert and adjuvant ingredients and for safety assessments to cover the full formulation rather than the active ingredient alone. That has not yet happened.

The Alternatives

Pointing to a problem without acknowledging that solutions exist is not honest. The alternatives are not as fast and they require more consistency and more patience. But they work, and the risk profile is not comparable.

The most accessible starting point is already under most growers' sinks. Potassium soap or green soap disrupts the cellular membranes and respiratory system of soft-bodied insects on contact. No systemic uptake, no residual in plant tissue, no accumulation in indoor dust. Effective against spider mites, aphids, thrips at certain stages, and mealybugs. The limitation is honest it only works when applied, and continuous application is needed. For growers with large collections that is a real consideration and will take a lot of time on a weekly basis.

Neem oil works similarly as a physical barrier, interrupting pest feeding and egg laying at the leaf surface without systemic uptake. The azadirachtin fraction adds insect growth regulation at low concentrations. The smell is genuinely unpleasant and like potassium soap it requires consistent application. Big caveat being that a thick layer of neem applied too frequently will block stomata and affect gas exchange, essentially suffocating the leaf tissue.

Biological controls take a different approach entirely. Hypoaspis miles for soil-dwelling pests, predatory mites for spider mite populations, parasitic wasps for specific pests in enclosed environments. These are living organisms that require patience to establish but once they are working, they maintain themselves.

Beyond direct intervention, environmental management is an option. Spider mites thrive in low humidity and high temperatures maintaining appropriate humidity for your plants suppresses populations without any intervention at all. Understanding what your pest needs and removing those conditions is not a substitute for all pest management, but it changes the baseline significantly.

And then there is the substrate itself. A plant growing in a biologically active substrate with a functioning rhizosphere microbiome is not a plant that will never encounter pests. But it is a plant with resilience that makes pest populations harder to establish and easier to manage when they do. The same principle as human gut microbiome research a disrupted microbiome creates vulnerability that a functioning one does not.

None of these will eliminate severely established infestation in a week. That is the honest trade-off. But the question is not only which approach works fastest it is which approach you want to be applying repeatedly. A healthy environment will not make you pest free. It will make your pest infestations more manageable. And more importantly, it keeps you healthier.

European Union

It is worth noting that as a European I do not have access to the systemic pesticides discussed in this post. The European Union has either banned or severely restricted the indoor household use of neonicotinoids, a regulatory decision that followed years of scientific review, growing evidence of environmental harm, and increasing pressure from independent researchers and member states. Regulators with access to the full toxicological data, including the proprietary studies that never make it into the public literature, looked at these compounds and decided they should not be freely available to consumers.

Denmark has gone further. In 2025 the Danish Environmental Protection Agency withdrew approval for 33 pesticide products for agricultural use not because of their active ingredients alone, but because those active ingredients break down into trifluoroacetic acid, TFA, a PFAS compound that does not degrade, contaminates groundwater, and is toxic to the reproductive system. The six active substances involved  fluazinam, fluopyram, diflufenican, mefentrifluconazole, tau-fluvalinate, and flonicamid  were approved and widely used. The EU risk assessment framework had not previously included information about TFA formation from these substances. It took a Danish research project, TriFluPest, carried out by the National Geological Survey of Denmark, to demonstrate what the standard regulatory process had missed. Denmark acted on the findings. Most of Europe has not yet.

The European Union maintains a list of approved basic substances and low-risk active substances for plant protection compounds derived from natural sources that have passed safety assessments for use in food production and ornamental horticulture. Among these are substances that are genuinely effective for pest management without the systemic chemistry profile that makes neonicotinoids concerning. Spinosad, derived from a naturally occurring soil bacterium Saccharopolyspora spinosa, is approved for use in the EU and is effective against thrips, fungus gnats, and caterpillars through a neural mechanism that is highly selective for insects. Pyrethrin, extracted from chrysanthemum flowers, is EU approved and acts as a fast-acting contact insecticide that degrades rapidly in light and air without the environmental persistence of synthetic pyrethroids. most are available at garden centres across Europe, and all of them have a risk profile that is categorically different from the synthetic systemic pesticides that currently dominate the hobby recommendation landscape.

A note on the alternatives both Spinosad and Pyrethrin are extremely toxic to aquatic life and should never be used near bodies of water. Pyrethrin carries its own human toxicity concerns, though its rapid breakdown in light and air significantly reduces chronic exposure risk compared to systemic compounds. It is worth noting also that many commercial Pyrethrin products contain piperonyl butoxide, a synergist that inhibits the enzymes insects use to break down Pyrethrin making it more effective but bringing its own documented toxicity and endocrine disruption concerns that do not appear on Pyrethrin-focused labels. The same principle applies here as everywhere else in this post. What makes these different than the systemics is not their toxicity but their cumulative nature where these substances tend to have short half-life the systemics are persistent, cumulative and will not break down. The enterohepatic circulation follow through the human body can lead to many problems in the long run and constant exposure will increase chances of these problems significantly.

My Position

I think systemic pesticides should not be available for indoor household use. Not because I think the people who use them are careless or uninformed but most people using them have no idea what is in the bottle. They trust that since it is in the store and available it is safe to use.  and that is not their failure, it is a failure of regulation.

The use of pesticides in an agricultural setting is an entirely different beast. But in your living room, your greenhouse, your home this is a constant and cumulative exposure. Is that really the trade we are making just for convenience?

References:

Cimino AM, et al. Effects of Neonicotinoid Pesticide Exposure on Human Health: A Systematic Review. Environmental Health Perspectives. 2017. 

Wang A, et al. Human exposure to neonicotinoids and the associated health risks: A review. Environment International. 2022. 

Ospina M, et al. Exposure to Neonicotinoid Insecticides in the U.S. General Population: Data from the 2015–2016 National Health and Nutrition Examination Survey. PMC. 2019. 

Mesnage R, Antoniou MN. Ignoring Adjuvant Toxicity Falsifies the Safety Profile of Commercial Pesticides. Frontiers in Public Health. 2018. 

Cox C, Zeiss M. Health, Pesticide Adjuvants, and Inert Ingredients: California Case Study Illustrates Need for Data Access. Environmental Health Perspectives. 2022. 

Sehgal N, et al. Invited Perspective: The Far Reach of PFAS — Inert Ingredients and Adjuvants in Pesticide Formulations. Environmental Health Perspectives. 2024. 

Ospina M, et al. Prevalence and Implications of Per- and Polyfluoroalkyl Substances (PFAS) in Settled Dust. PMC. 2025. 

Sheets LP, et al. A critical review on the potential impacts of neonicotinoid insecticide use. PMC. 2024. 

Denmark bans 33 PFAS Pesticides | Agrolab