friend or foe, good bad and ugly

By Geoff Hawkins, 1st July 2026

Pest Control Methods

Four main approaches:

• Prevention: physical barriers, deterrent products placed around plants

• Contact pesticides: must physically touch the pest; useless without active infestation

• Systemic pesticides: absorbed into plant tissue, kills sap-sucking pests; RHS now advises against (enters food chain)

• Biological controls: species-specific predators (nematodes, parasitic wasps, predatory mites)

• Plant invigorator: milk-based, organic; blocks breathing pores + boosts plant resilience

• Integrated Pest Management (IPM): contact first, then introduce predators

• Pheromone traps: effective for codling moth and box tree moth; males lured onto sticky base

• Check RHS website for current approved pesticides; names change annually, active chemicals change too

Common Pests and Controls

Slugs and snails

• Only ~2 of 44 UK species are genuine garden pests

• Leopard slug is carnivorous: eats other slugs, leave it alone

• Beer traps catch mostly beneficial slugs; not recommended

• Nematodes: most targeted control available

Aphids

• Ants farm aphids, protecting them from predators (ladybirds, lacewings)

• Jet of water: first-line control for most aphid types

• Woolly aphids on apple trees: jet of water exposes them to birds

• Lupin aphid: one individual can theoretically produce 300,000 offspring

• Brown, swollen aphids = parasitized by wasp larvae; do not squash

• Blackcurrant/redcurrant leaf blister: pinch and dispose of affected leaves

• Black Bean aphids: take tip off aphids at end of May

• Mullein Moth on verbascums

Caterpillars and sawflies

• Cinnabar moth on ragwort: leave alone, plant-specific

• Box tree moth: nematode spray (caterpillar must be present); pheromone trap available

• Gooseberry sawfly: delay netting so birds can access; contact organic spray if needed

• Lily beetle: catch adults on newspaper; squash eggs; larvae disguise as bird droppings

• Cabbage white: fine butterfly netting (no gaps); nematodes as biological control

• Parasitized caterpillars (white pupae on outside): leave, will produce 50+ predatory wasps

• Elephant Hawk moth caterpillar on Fuchsias, very beautiful with pink/yellow stripes

Other pests

• Vine weevil larvae: destroy roots silently; nematodes for control

• Red spider mite: greenhouse pest; predatory mite as biological control; must catch early

• Scale insects: cause sooty mould; treat with horticultural soap

• Flea beetle: wave yellow sticky traps over plants to catch as they leap

• Capsid bugs: damage buds before visible; cut off affected growth, no spray remedy

• Allium leaf miner: full fleece cover over leeks is the only reliable control

• Cock chafer bugs: can do damage by feeding on plant roots: use nematodes for chafers

Beneficial Insects to Protect

Ladybirds

• Larvae eat ~300 aphids per week; often mistaken for pests (black, spiky)

• Harlequin ladybirds: non-native but still eat aphids

Hoverflies: larvae eat aphids; adults pollinate; commonly mistaken for wasps

Lacewings: overwinter in sheds and greenhouses; open windows in spring to release

Parasitic wasps: lay eggs inside aphids and caterpillars; do not disturb

Wasps: feed larvae on caterpillars and aphids; only seek sweet food in autumn (no grubs left)

• Wasp trap tip: spoonful of jam; yellow-legged hornet sightings must be reported to the National Bee Unit

Leaf cutter bee: beneficial pollinator; oval leaf cuts in roses are harmless

Bug hotels: provides overwintering habitat for lacewings, ladybirds, hoverflies, beetles

Diseases and Disorders

Diseases: spores and viruses always present in atmosphere; stressed plants are more susceptible

• Spray preventatively; once on the leaf, damage is permanent

• Rust (leeks, garlic, hops): unavoidable, live with it

• Potato and tomato blight: choose resistant varieties; July blight and late blight are distinct

• Peach leaf curl: cover with plastic December to March; removes moisture from buds

• Honey fungus: rhizomorphs spread up to 60ft; no reliable control; remove affected plants

• Clubroot in brassicas: crop rotation or resistant varieties

Disorders (physiological, not infectious)

• Fasciation: flowers/stems expand unusually; not reproducible from seed

• Blossom end rot on tomatoes: calcium deficiency from irregular watering, not physical damage

• Magnesium deficiency (yellowing leaves): treat with Epsom salts

Lichen on trees: sign of clean air, not a problem

Garden Wildlife and Soil Life

Beneficial soil creatures

• Centipedes (1 pair of legs per segment): active predators, highly beneficial

• Millipedes (2 pairs per segment): minimal damage, largely harmless

• Ground beetles: predatory, hunt slugs and other pests

• Slow worms: found in compost heaps, eat slugs

Frogs, toads, hedgehogs: valuable pest controllers; ensure fence gaps for movement between gardens

Birds

• Blue tits: heavy caterpillar feeders in spring

• Blackbirds and thrushes: scratch for soil pests; blackbirds territorial, will drive out thrushes

• Starlings: signal leather jacket or chafer grub infestations in lawns

Moles: tunnel traps most humane; avoid chemical controls (enter food chain via predators)

Grey squirrels: illegal to release if trapped; must be killed

Ivy: excellent nectar source and wildlife habitat; only problematic when reaching tree canopy

Key Principles

Avoid mass eradication: kills beneficial insects alongside pests

Finger and thumb: most effective tool for eggs, small larvae, and leaf miners

Stop winter washing: destroys natural predators; speaker stopped decades ago, woolly aphid disappeared within 3 years

Inspect plants in the evening: catch caterpillars and pests before damage escalates

Biological controls require active infestation: wasted money if pest is absent

Ragwort note: cinnabar moth caterpillars that devour ragwort can make it perennial (prevents seed cycle), perpetuating the plant rather than controlling it

Ants on aphids: removing aphid colonies also removes the ants farming them; address the ants to protect aphid predators

Next Steps

Check RHS website for current approved pesticide list

Product names and active chemicals change annually; last year's bottle may differ from this year's.

Install a bug hotel or overwintering habitat in the garden

Supports lacewings, ladybirds, and hoverflies through winter for early-season predation.

Cover peach or nectarine trees with plastic sheeting

Apply in December, remove in March to prevent peach leaf curl by blocking moisture from buds.