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Gardening glossary

Integrated pest management (IPM)

Integrated pest management (IPM) is the framework most modern horticulture, agriculture, and increasingly home gardening builds on. It explicitly rejects the "see pest, spray pest" reflex in favour of a tiered approach that uses chemical control only when other methods have failed and only with the least disruptive product available.

The US EPA defines IPM as "an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices." The framework has four well-defined tiers:

**1. Set action thresholds.** A single aphid is not a pest problem; a colony of 200 is. IPM defines, in advance, the population level or damage level at which control becomes worthwhile. For tomato hornworm, that might be one larva per plant. For aphids on a houseplant, you might tolerate 10 but act on 50. Below threshold, you watch and do nothing.

**2. Monitor and identify.** Walk the garden weekly. Check the undersides of leaves. Use yellow and blue sticky cards in greenhouses. Identify what you find using a hand lens and a guide — many "pests" are actually beneficial predators or harmless visitors.

**3. Prevention.** - Choose resistant varieties (look for VFN, mildew-resistant, etc., codes). - Rotate crops on a 3–4 year cycle. - Encourage beneficial habitat with flowering plants (calendula, alyssum, dill, fennel). - Maintain soil health — strong plants resist pests far better than stressed ones. - Exclude pests physically with [row cover](/glossary/row-cover) fleece and netting. - Sanitise — remove infected debris, sterilise propagation tools and pots.

**4. Control (only if thresholds are exceeded and prevention failed).** IPM ranks control methods from least to most disruptive: - Physical (hand-picking, water spray, traps). - Cultural (changing watering, pruning, spacing). - Biological ([biological control](/glossary/biological-control) using predators, parasitoids, or biopesticides like *Bacillus thuringiensis*). - Selective chemical (insecticidal soap, horticultural oil, neem) used only where biological control is failing. - Broad-spectrum chemical (synthetic pyrethroids, etc.) — last resort, applied selectively to affected plants only.

A simple IPM rhythm for a home garden:

1. **Weekly scout.** Five minutes per bed. Note what you see. 2. **Resist the urge to spray.** Most populations self-regulate as predators arrive. 3. **Intervene physically first.** Hose off aphids. Hand-pick hornworms. Bag and bin diseased leaves. 4. **Escalate biologically.** Release beneficials for a recurring problem. 5. **Spray only if a threshold is exceeded** and only the affected plant(s), preferably in the evening when bees are not foraging.

The transformation in most home gardens after one season of IPM is the same: pest pressure drops, beneficial insects return, fewer crops fail, and the spray cabinet empties itself.

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Related terms

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.

Systemic insecticide

A systemic insecticide is absorbed by the plant and moves through its tissues, killing sap-sucking insects that feed on the treated plant. Neonicotinoids are the best-known class — but they are heavily restricted in the UK and EU because of harm to pollinators. Use is now banned outdoors in the UK as of 2025.

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.