James Whitaker
Why Aphids Are Worth Taking Seriously
Few sights are more disheartening on a summer morning than the tips of your broad beans curled and sticky, crawling with pale green insects. Aphids are small, soft-bodied sap-suckers, and there are hundreds of species in the UK. Some are fussy eaters — the blackfly that plague runner beans, the cabbage aphid that clusters on brassicas — while others are generalists happy to nibble on almost anything.
The direct damage is bad enough. Aphids pierce tender shoots and drain the sap, leaving leaves curled, distorted and stunted. But the real trouble is what follows. As they feed, aphids excrete a sugary honeydew that coats leaves and encourages sooty mould, which blocks light and slows growth. Worse still, they act as couriers for viruses such as cucumber mosaic and potato leafroll, which can ruin a crop even after the aphids themselves have gone.
The good news is that you do not need a cabinet of harsh chemicals to deal with them. On an allotment or in a kitchen garden, a mixture of vigilant observation and natural predators will usually keep numbers down to a tolerable level.
Start by Watching Rather Than Spraying
Aphid populations explode quickly, but they also crash. Before you reach for anything at all, spend a few days inspecting your plants. Look at the growing tips of beans, the undersides of brassica leaves and the flower buds of roses and fruit bushes — these are the favourite hiding places.
Check twice a week through late spring and early summer, when colonies build fastest. If you find a small cluster, you can often deal with it by hand. Wipe them off with a gloved finger, or squirt them away with a sharp jet of water from a hose or spray bottle. On sturdy plants, a strong blast every few days knocks aphids to the ground, where they struggle to climb back before ground beetles and other predators find them.
- Remove badly infested tips — pinch out the top few inches of beans or nasturtiums and bin them, rather than composting.
- Inspect new plants before planting them out, especially anything bought from a garden centre.
- Keep a notebook of when aphids appear each year — you will learn your plot's rhythm and can act earlier next season.
Encourage Ladybirds, Lacewings and Hoverflies
Nature already provides the best aphid control you could ask for. A single ladybird larva can eat dozens of aphids a day, and a hoverfly larva will happily munch its way through hundreds. Your job is simply to make your plot a place they want to stay.
The key is to avoid the temptation to clear every corner. Leave a patch of nettles, which many aphids prefer over your crops and which also support ladybirds and lacewings. Allow a few umbellifer flowers — dill, fennel, coriander, yarrow and parsley left to bolt — because their flat flower heads are magnets for hoverflies and parasitic wasps. A small wildflower strip along a fence will do more for pest control than any bottle from the shop.
Think carefully before using even organic sprays. A soap spray will kill aphids, but it will also kill the ladybird larvae feeding on them. If you can wait a week and let the predators catch up, you will often find the problem resolves itself. Where you must intervene, treat only the affected plant and avoid spraying open flowers.
Soap Sprays Done Properly
When aphids are winning and the predators have not yet arrived, a soap spray is a sensible, low-impact tool. It works by breaking down the waxy coating on the aphid's body, so it must make direct contact to be effective. It leaves no residue and breaks down quickly in sunlight.
Use a pure liquid soap — one without detergents, perfumes or antibacterial additives, as these can damage your plants. Mix roughly a teaspoon of soap into a litre of water in a spray bottle. Test it on a single leaf first, wait a day, and check for scorching before treating the whole plant.
- Spray in the cool of the evening, never in full sun or when temperatures are above about 25°C.
- Aim at the undersides of leaves and the growing tips, where aphids cluster.
- Repeat every four to five days for a fortnight, as soap does not kill eggs.
- Rinse edible leaves before eating, and avoid spraying seedlings or anything with hairy or waxy foliage.
Companion Planting and Physical Barriers
Some plants genuinely do seem to confuse or repel aphids, and even if the science is mixed, the flowers and scent are a pleasure in their own right. Strongly scented herbs — mint, chives, garlic, coriander and basil — are traditional companions for brassicas, beans and lettuce. French marigolds are worth tucking between tomatoes and in the greenhouse border.
Nasturtiums are the classic sacrifice crop: aphids adore them and will colonise the nasturtiums before your beans. Plant a few at the end of each row and check them regularly, removing the worst leaves before the insects move on.
Physical barriers help too. Fine insect-proof mesh over brassicas and carrots stops aphids landing in the first place, though you must keep it securely pinned down. Reflective silver mulch can disorient winged aphids looking for a landing site. And remember that the winged generation produced in late summer is what flies off to new hosts, so a tidy plot with fewer overwintering weeds gives them fewer places to hide.
Stay Calm and Keep the Balance
A perfect allotment with not a single aphid is not the goal, and chasing one will only drive you to the chemicals you are trying to avoid. A healthy plot is a busy one, with birds, beetles, ladybirds and hoverflies all doing their share.
Accept a little damage, act early when a colony builds, and let the garden's own predators do the heavy lifting. Squash a few by hand, spray sparingly and only where needed, and keep something flowering for the insects that help you. Do that, and your beans, brassicas and roses will come through the summer just fine.
