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Gardening glossary

Systemic insecticide

A systemic insecticide is one that enters a plant's vascular system and moves with sap from roots to shoots, or from sprayed leaves into adjacent tissue. Any insect that pierces and sucks plant sap — aphids, whiteflies, scale, mealybugs, leaf hoppers — ingests the chemical and dies. Contact insecticides, by contrast, only kill insects that touch the spray directly.

The dominant class of systemic insecticides since the late 1990s has been the **neonicotinoids** — synthetic compounds (imidacloprid, thiamethoxam, clothianidin, acetamiprid, dinotefuran) that target the nicotinic acetylcholine receptors in insect nervous systems.

**UK regulatory status (current to early 2025):**

- **Outdoor agricultural use of three key neonicotinoids — clothianidin, thiamethoxam, imidacloprid — has been banned in the UK since 2018** due to harm to bees and other pollinators. - **For the first time in five years, the UK government in January 2025 refused emergency authorisation** of thiamethoxam (Cruiser SB) for use on sugar beet — closing a previously-used annual exception. - The UK government has stated it is working toward complete legislative bans on these three neonicotinoids, including blocking future emergency authorisations. - **Acetamiprid** remains approved in the UK for some uses, including some garden products, because regulatory bodies consider its environmental profile less harmful. - Some neonicotinoid use remains permitted in fully-enclosed commercial greenhouses where bees are not exposed.

**Home gardener availability in the UK** is now extremely limited. Most garden-centre neonicotinoid products have been withdrawn from sale. Remaining systemic products often use acetamiprid, spirotetramat, or flupyradifurone.

**Why the bans?**

- Neonicotinoids translocate into nectar and pollen, exposing bees and other pollinators to sub-lethal and lethal doses. - Documented effects include impaired bee navigation, weakened immune systems, reduced colony survival, and harm to wild pollinators including bumblebees and solitary bees. - Residues persist in soils for years and leach into water bodies, affecting aquatic invertebrates.

**Safer alternatives for the home gardener:**

- Insecticidal soap and horticultural oil for aphids, mites, whiteflies, scale, and mealybugs. - Neem oil (azadirachtin) — botanical, partly systemic, breaks down quickly. Avoid during bloom. - *Bacillus thuringiensis* (Bt) for caterpillar pests — extremely selective, safe for bees. - Biological controls — ladybirds, lacewings, parasitic wasps, predatory mites. - Integrated pest management (see [IPM](/glossary/ipm)).

If a systemic insecticide is genuinely needed, confine use to non-flowering ornamental houseplants and follow label restrictions strictly. Never apply to anything bees may visit.

[Sources: GOV.UK pesticide emergency authorisation news (January 2025); Garden Organic and The Wildlife Trusts UK neonicotinoid guidance.]

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Related terms

Integrated pest management (IPM)

Integrated pest management is the EPA-recognised, environmentally-sensitive framework for pest control. It combines pest monitoring, action thresholds, prevention, biological controls, and targeted chemical sprays — used only as a last resort — to manage pests with the lowest possible risk to people, beneficial wildlife, and the environment.

Biological control

Biological control is pest management using living organisms — predators, parasitoids, pathogens — instead of synthetic chemicals. Examples: ladybirds for aphids, Encarsia formosa parasitic wasps for whitefly, nematodes for vine weevil grubs, and Bacillus thuringiensis for caterpillars.

Plant quarantine

Plant quarantine is the practice of isolating new, sick, or recently-imported plants from the rest of your collection for 2 to 4 weeks to make sure they are not carrying pests or disease. The single highest-leverage habit for protecting an indoor plant collection.

Neem oil

Neem oil is a yellow-brown vegetable oil pressed from the seeds of Azadirachta indica (the neem tree). Diluted as a foliar spray, it acts as a contact suffocant, feeding deterrent, and partial systemic against aphids, whiteflies, thrips, mites, scale, and some fungal diseases. Generally low-toxicity to mammals but harmful to bees if sprayed directly.

Aphid

Aphids are tiny pear-shaped sap-sucking insects, usually green, black, or pink, that cluster on new growth and undersides of leaves. They reproduce rapidly and excrete sticky honeydew that fuels sooty mold.