Problems & pests

Possible causes

35 problems

• Allium leaf miner

  Phytomyza gymnostoma

  A tiny fly whose larvae tunnel down leek and onion stems, leaving brown pupae behind. Lines of white dots on the leaves are the giveaway. Keep crops under mesh in spring and autumn when the adults fly.

  PestSerious

• Aphids

  Aphidoidea

  Aphids breed astonishingly fast in spring, but ladybirds, hoverflies and blue tits usually catch up. Squash early clusters by hand and avoid sprays that kill the predators doing the work for you.

  PestModerate

• Big bud mite

  Cecidophyopsis ribis

  Microscopic mites live inside blackcurrant buds, which swell into round 'big buds' and fail to open. The mite spreads reversion virus. Pick off swollen buds in winter and replace badly infested or reverted bushes.

  PestSerious

• Blossom end rot

  Blossom end rot is a calcium shortage in developing fruit, almost always caused by irregular watering rather than poor soil. Water steadily, especially in pots and growbags, and later trusses will usually be fine.

  Growing conditionModerate

• Box blight

  Calonectria pseudonaviculata and Pseudonectria foliicola

  Box blight causes brown leaf patches, rapid leaf drop and black streaks on stems, mostly in warm, wet weather. Clear fallen leaves, prune less often, keep foliage dry and consider resistant alternatives.

  DiseaseSerious

• Box tree caterpillar

  Cydalima perspectalis

  Check the inside of box plants from March for green-and-black caterpillars and webbing. Catch them early by hand or with a biological spray, and use pheromone traps to time your checks.

  PestSerious

• Cabbage caterpillars

  Pieris brassicae, Pieris rapae, Mamestra brassicae

  Fine insect mesh fitted over brassicas before the butterflies arrive is the simplest answer. Otherwise, check leaf undersides weekly in summer and rub off yellow egg clusters before they hatch.

  PestModerate

• Carrot fly

  Chamaepsila rosae

  Carrot fly larvae tunnel into roots, leaving rusty brown channels. A fine mesh cover or a 60 cm barrier around the bed keeps the low-flying females from laying eggs.

  PestModerate

• Chocolate spot

  Botrytis fabae

  Chocolate-brown spots on broad bean leaves, stems and flowers, worst in damp, crowded or waterlogged crops. Plants often grow through mild attacks; space them well, keep drainage good and clear debris.

  DiseaseModerate

• Clubroot

  Plasmodiophora brassicae

  Clubroot is a soil-borne brassica disease that can persist for decades. You cannot eradicate it, but liming acid soil, improving drainage, raising transplants well and growing resistant varieties keep crops going.

  DiseaseSerious

• Damping off

  Pythium, Rhizoctonia and Phytophthora species

  Damping off makes young seedlings collapse at soil level. Sow thinly in fresh compost and clean trays, use tap water, avoid overwatering and give plenty of light and air. Affected seedlings cannot be saved.

  DiseaseModerate

• Downy mildew

  Yellow or pale blotches on top of leaves with grey, white or purplish fuzz underneath, in cool, damp weather. Remove infected leaves, improve air flow, water the soil not the leaves and choose resistant varieties.

  DiseaseModerate

• Drought stress

  Prolonged dry weather causes wilting, scorched leaves and poor cropping, with some damage showing months later. Water deeply and less often, mulch generously and choose drought-tolerant plants for dry spots.

  Growing conditionModerate

• Flea beetle

  Phyllotreta spp.

  Tiny jumping beetles pepper the leaves of radish, rocket and young brassicas with small round holes. Older plants shrug it off; keep seedlings growing fast with water and cover them with fleece in dry spells.

  PestMinor

• Frost damage

  Frost blackens soft growth, browns evergreen leaves and kills blossom. Do not prune damaged shoots straight away; wait until frosts are over, then cut back to healthy growth. Protect tender plants on clear, still nights.

  Growing conditionModerate

• Glasshouse whitefly

  Trialeurodes vaporariorum

  Tiny white flies rise in a cloud when you brush greenhouse plants. Hang yellow sticky traps early, introduce the parasitic wasp Encarsia once it is warm, and clear the greenhouse in winter.

  PestModerate

• Grey mould

  Botrytis cinerea

  Grey mould attacks soft, damaged or dying tissue in cool, damp, still air. Remove mouldy material promptly, ventilate greenhouses, avoid overcrowding and water in the morning.

  DiseaseModerate

• Honey fungus

  Armillaria mellea and other Armillaria species

  Honey fungus kills trees and shrubs by rotting their roots. Confirm it by finding white fungal sheets under the bark at the base, dig out infected stumps and roots, and replant with less susceptible species.

  DiseaseSerious

• Leatherjackets

  Tipula paludosa

  Brown, dead patches of lawn that birds pull apart in spring often hide leatherjackets. Confirm by covering a wet patch overnight, then apply a nematode drench in autumn while soil is still warm.

  PestModerate

• Leek moth

  Acrolepiopsis assectella

  Small caterpillars mine and chew leek and onion leaves, leaving pale patches, holes and frass, and may bore into the centre. Pick them off, remove cocoons and grow under fine mesh from April.

  PestModerate

• Lily beetle

  Lilioceris lilii

  Bright scarlet beetles and grubs coated in dark slime can strip lilies by midsummer. Check plants every few days from March and squash every beetle, egg and larva you find.

  PestSerious

• Onion fly

  Delia antiqua

  Seedling onions turn yellow, flop over and pull up easily, with white maggots in the base. Onion sets are less prone; cover seed-sown onions with fine mesh and avoid bruising them when thinning.

  PestModerate

• Onion white rot

  Stromatinia cepivora

  A soil-borne fungus that rots the roots and base of onions, garlic and leeks, leaving white fluff and tiny black specks. There is no cure; remove plants with their soil and keep alliums off that bed for many years.

  DiseaseSerious

• Parsnip canker

  Itersonilia pastinacae

  Rough, orange-brown to black patches on the shoulders of parsnips, which can crack and rot. Grow resistant varieties, sow a little later, space closely for smaller roots and avoid damaging the crowns.

  DiseaseModerate

• Pea moth

  Cydia nigricana

  Pale caterpillars eat the peas inside the pods, and you only notice when shelling. Crops flowering from early June to late July are at risk, so early or late sowings and mesh avoid most damage.

  PestModerate

• Plant viruses

  Viruses cause mottled, mosaic or streaked leaves, distorted growth, stunting and poor crops. There is no cure: remove infected plants, control sap-sucking pests, keep tools clean and buy certified virus-free stock.

  DiseaseModerate

• Potato and tomato blight

  Phytophthora infestans

  Blight spreads fast in warm, wet summer weather and can flatten potato and tomato foliage within days. Act at the first brown patch, cut off the haulm, and grow resistant varieties.

  DiseaseSerious

• Powdery mildew

  Erysiphales (e.g. Podosphaera, Erysiphe, Golovinomyces)

  A white, flour-like dusting on leaves that thrives when roots are dry but the air is humid. Water at the base, mulch, improve airflow and grow resistant varieties before reaching for any spray.

  DiseaseModerate

• Red spider mite

  Tetranychus urticae

  Tiny sap-feeding mites thrive in hot, dry greenhouses. Raise humidity, check leaf undersides with a hand lens and introduce predatory mites early, before webbing appears.

  PestSerious

• Rose black spot

  Diplocarpon rosae

  Black spot is the commonest rose disease and spreads in rain splash. Clear fallen leaves, water at the base, prune for airflow and choose resistant roses; healthy plants shrug off the odd spot.

  DiseaseModerate

• Rosemary beetle

  Chrysolina americana

  Shiny purple-and-green striped beetles feed on rosemary and lavender mainly from autumn to spring. Shake plants over newspaper and collect them; established shrubs usually shrug off the damage.

  PestMinor

• Rust

  Pucciniales (e.g. Puccinia allii, Phragmidium mucronatum)

  Rusts produce orange, brown or black powdery pustules, usually on leaf undersides. Most are a cosmetic nuisance; remove affected leaves, improve airflow, rotate crops and grow resistant varieties.

  DiseaseMinor

• Slugs and snails

  You will never get rid of slugs and snails, so protect what matters most: raise tender seedlings until they are sturdy, patrol by torchlight after rain and welcome frogs, thrushes and ground beetles.

  PestSerious

• Viburnum beetle

  Pyrrhalta viburni

  In late spring, small grubs turn viburnum leaves into lace; in summer, brown beetles add more holes. Pick off larvae early and prune out twigs holding egg sites over winter.

  PestModerate

• Vine weevil

  Otiorhynchus sulcatus

  Notched leaf edges are a warning; the real damage is done by cream grubs eating roots. Apply nematodes to pots in late summer and early autumn, and check new plants before potting them up.

  PestSerious

Nothing matches every choice. Untick a plant part or problem type, or try fewer symptoms.