Common pests and diseases on UK allotments

Watch on Broad beans, brassicas, roses and most soft growth

Green, black or grey aphids gather on soft growth, including broad bean tips and the undersides of brassica leaves. They breed quickly in late spring and leave sticky honeydew, which can grow black sooty mould. Most colonies can be squashed by hand or washed off with a hard jet of water, and ladybirds and hoverfly larvae often reduce the rest.

Watch on Kale, sprouts, cabbage and other brassicas

Cabbage whitefly are tiny white insects that rise from the underside of a brassica leaf when it is disturbed. They overwinter on kale and sprouts and can keep feeding through winter, leaving honeydew and sooty mould on lower leaves. The outer leaves are usually worst affected, so the crop is often usable once those leaves are stripped and composted.

Watch on Beans, cucumbers, aubergines and tunnel crops

Red spider mite does most harm in hot dry air, especially under glass and on beans, cucumbers and aubergines in a polytunnel. Leaves develop fine pale speckling, then dry and turn bronze. A heavy attack can leave faint webbing over the shoot tips. Higher humidity and steady watering slow it down.

Watch on Potatoes, beans, currants and dahlias

Capsid bugs are quick green insects that feed on young leaves and shoot tips. The damage shows later as small ragged holes with brown edges across the opened leaf. Potatoes, beans, currants and dahlias are often affected. The leaves can look rough, but the plant usually grows on without treatment.

Watch on Seedlings, salad leaves, potatoes and beans

Slugs and snails feed after dark and in wet weather. They can strip seedlings, salad leaves and hostas down to the stalk overnight. Look for slime trails on the soil and pots in the morning. Protect young plants with barriers and check for slugs in the evening.

Watch on Cabbage, kale, sprouts and other brassicas

Cabbage white caterpillars hatch from yellow eggs on the undersides of brassica leaves. They feed from midsummer and can bore into cabbage hearts. Yellow-and-black caterpillars feeding in groups are large whites; green caterpillars feeding alone are small whites. Squash eggs when you find them, and cover the bed with fine netting before butterflies lay.

Watch on Rocket, radish, turnip and brassica seedlings

Flea beetles make dozens of small round holes in rocket, radish, turnip and brassica seedlings. A bad attack can check or kill a young row. The tiny dark beetles jump away when your hand moves over them. They are worst in warm dry spells on slow-growing seedlings, so water well and cover with fleece until the plants are larger.

Watch on Peas and broad beans

Pea and bean weevils cut neat U-shaped notches from the leaf edges of peas and broad beans in spring. On a strong plant the damage is mostly cosmetic, but on a cold slow seedling it can hold growth back. Sow once the soil has warmed so seedlings grow away quickly.

Watch on Gooseberries, currants and Solomon's seal

Sawfly larvae look like caterpillars and feed in the same way. They can strip gooseberries, currants and Solomon's seal from the middle of the plant outward, sometimes leaving bare stems within a few days. Count the fleshy legs to tell them apart: sawfly larvae have more pairs than moth caterpillars. Check the middle of the bush from late spring and pick them off early.

Watch on Brassicas, peas and beans

Wood pigeons strip brassicas through winter and damage pea and bean seedlings in spring. They leave ragged leaves and bare stalks, with no slime trail and no caterpillar droppings. A flock can clear a bed of greens quickly. Netting or a fruit cage is the most reliable protection.

Watch on Leeks, onions and garlic

Leek moth has spread widely in recent years. Its caterpillars mine into the leaves and stems of leeks, onions and garlic, leaving whitish tunnels and windows. Damaged tissue can then rot. Two or three generations can occur from spring to autumn. Cover the row with mesh from planting, and clear and compost the crop debris the moth overwinters in.

Watch on Potatoes and outdoor tomatoes

Late blight often ends the outdoor tomato and maincrop potato season. It strikes in warm humid spells from midsummer, browning and collapsing the foliage within days and rotting the tubers and fruit. There is no cure once it arrives, so grow resistant varieties, space plants for airflow, and lift potatoes before a bad attack reaches them.

Watch on Courgettes, squash, peas and marrows

Powdery mildew puts a white dusty coating on courgette, squash, pea and marrow leaves from late summer. It is worst on plants that have run short of water at the root. It seldom kills an established crop, but it shortens the season and slows growth. Keep plants watered and mulched, and remove the worst leaves to slow it down.

Watch on Onions, brassicas, lettuce and spinach

Downy mildew causes angular yellow patches on the upper leaf, with greyish mould underneath. It affects onions, brassicas, lettuce and spinach in cool wet weather. It is a water mould rather than a true fungus, so it spreads in damp conditions and often returns in the same weather. Wider spacing, crop rotation and clearing old leaves help reduce it.

Watch on Cabbage, cauliflower, sprouts and swede

Clubroot swells brassica roots into distorted clubs, so the plant wilts by day and never bulks up well. The organism survives in the soil as resting spores for twenty years, so an affected plot needs long-term management rather than a cure. Lime the ground to lift the pH, rotate brassicas as widely as the plot allows, and raise strong plants in pots before planting out.

Watch on Leeks, garlic, beans and mint

Rust appears as raised orange, brown or dark pustules on the undersides of leaves. Different rusts affect leeks, garlic, beans and mint. Rust marks the crop and weakens growth, but it often does not kill the plant outright. Space and rotate crops to keep air moving, water at the root rather than over the leaves, and clear infected material off the plot.

Watch on Strawberries, tomatoes, lettuce and soft growth

Grey mould, or botrytis, is the fuzzy grey-brown growth that rots soft fruit, ripening tomatoes and wounded or dying tissue in cool damp conditions. It can move from dead leaves and spent flowers into healthy growth, so it is worse in crowded, poorly ventilated tunnels. Pick affected parts off into a bag, improve the airflow, and prune cleanly.

Watch on Potatoes

Common scab causes rough corky patches on potato skins. It is worst on light limey soils in a dry season. The damage is only on the skin, and the tubers peel and eat well, so it is a cosmetic fault rather than a threat to the crop. Water in dry spells as the tubers form, work in plenty of organic matter, and choose resistant varieties on affected plots.

Watch on Onions, garlic, leeks and shallots

White rot is the most serious disease of the onion family. It rots the base of the bulb and spreads a fluffy white mould with tiny black resting bodies over the roots. Those bodies survive in the soil for many years, so an infected plot stays infected. Lift and bin affected plants, never move soil or bulbs off the bed, and rest the ground from alliums for as long as you can.

Watch on Potatoes, carrots, onions and seedlings

Wireworms are the thin, tough, orange-brown larvae of click beetles. They bore narrow tunnels through potatoes and into carrots, onions and seedling stems. They are worst in the first few years after grass is dug up, and they fade as the ground is worked. Lift maincrop potatoes promptly so the tunnelling does not spread, and dig the plot over in autumn to expose them.

Watch on Seedlings, brassicas and root crops

Leatherjackets are fat greyish legless crane fly grubs. They chew through roots and stem bases in spring, thinning seedbeds and leaving bare patches. They are most common on ground that was grass the year before. Fork the bed through in autumn and firm new seedlings in well so grubs cannot pull them under.

Watch on Strawberries and container plants

Vine weevil is worst in containers. The fat white C-shaped grubs eat the roots of strawberries, primulas and many potted plants until the plant lifts away with few roots left. The dull black adults notch leaf edges by night but do little real harm. Treat the grubs with the right nematode, and turn out suspect pots in spring or autumn to check for them.

Watch on Lettuce, brassicas and beetroot

Cutworms are the caterpillars of night-flying moths. They live near the soil surface and cut through the stems of young lettuce, brassicas and beet at ground level, making the plant collapse. Scratch the soil around a cut seedling and you may find the fat grey grub. Hoe regularly to expose them, keep weeds down, and protect important rows with collars.

Watch on Carrots, parsnips, celery and celeriac

Carrot fly larvae make rusty-brown tunnels just under the skin of carrots, parsnips and celery. The first sign above ground is often a reddish tinge to wilting foliage. The low-flying adults find the crop by scent, especially when you thin or lift it. Sow thinly to avoid thinning, and screen the bed with fine mesh or a low barrier.

Watch on Brassica transplants and swede

Cabbage root fly maggots eat the roots of newly planted brassicas. The plant grows slowly, wilts in the sun and can pull straight out of the ground. Transplants and swedes are most at risk. Fit a collar of card or felt around each stem at planting to stop the fly laying eggs beside it, or cover the whole bed with mesh from planting day.

Watch on Potatoes, tomatoes and many vegetables

Potato cyst eelworm and root-knot nematodes are microscopic worms that attack roots from within. Affected potatoes or tomatoes grow poorly, yellow early and die back, with tiny cysts or knobbly galls on the roots. Numbers build the more often you grow the same crop, so rotation is the main defence. Grow resistant potato varieties and rest infested ground from the crop for several years.