Radish

Stages affected: Germination · Seedling · Vegetative

Tiny dark beetles that jump like fleas when disturbed and pepper leaves with small round holes. Established plants shrug them off, but on seedlings and on a crop grown for its leaves the damage matters, and on radish and other brassicas they arrive in numbers early in the season.

Visual signs

Beetle 1.5 to 3 mm long usually shiny black bronze or metallic blue and sometimes with a pale stripe down each wing cover · Jumps away instantly when you lean over the plant which is the surest identification · Enlarged hind legs visible if you can get one to hold still · Found on the upper leaf surface in sunshine and most active on warm still days · Pale larvae feed unseen on roots and do little damage on most crops

Damage pattern

Many small round holes 1 to 2 mm across giving the leaf a shot-through or peppered look · Damage heaviest on the youngest leaves and at the edges of a bed nearest cover · Seedlings can be killed outright or checked so badly they never catch up · Older established plants carry the damage without losing yield, so the holes alone are not a reason to act · On root crops the holes cost nothing directly; the risk is a seedling set back at the stage when the root should be forming

Stages affected: Seedling · Vegetative · Maturation

Not a disease. A bed of healthy leafy plants that never form a usable root, which is the single commonest way a radish or turnip sowing disappoints. It has three ordinary causes and they are all decided in the first two weeks: sown too thickly and never thinned, too little light, or too much nitrogen. None of them can be corrected once the window has passed.

Visual signs

Vigorous healthy leaves with no swelling at the base of the stem, or a thin stringy root like a pencil lead · Plants standing shoulder to shoulder in the row with leaves overlapping · Leaves unusually large dark and lush where nitrogen is the cause · Leaves pale and stretched with long thin stalks where light is the cause · No insect damage no galls and no rot: pull one up and there is simply nothing there

Damage pattern

Affects the whole sowing evenly rather than appearing in patches, which is what separates it from anything soil-borne · Plants look healthy throughout, so it is usually discovered at the intended harvest date · Recurs in exactly the same way in the next sowing if the cause is not changed · Never spreads and carries no risk to the next crop

Stages affected: Maturation · Harvest window

Not a disease. A root that has gone dry and woolly inside, or so pungent it is unpleasant to eat, or both. It is the price of leaving a fast crop too long, of growing it in heat, or of letting the bed dry out. The outside often looks perfect, so it is usually discovered when the radish is cut or bitten.

Visual signs

Outside often looks normal; the fault is inside · Cut across and the flesh is dry and woolly or has a hollow or spongy centre instead of being solid white · Sometimes accompanied by cracks or splits in the skin from uneven watering · A flower stalk rising from the crown means the plant has bolted and the root will always be woody · Roots noticeably larger than the variety should be at maturity

Damage pattern

Affects the oldest and largest roots in a sowing first, so the row deteriorates from the earliest-maturing plants · Comes on quickly: a crop can go from perfect to pithy in under a week in warm weather · Follows a hot spell or a dry spell, or simply follows the harvest date by too many days · Never spreads and leaves the ground unaffected · Not reversible: watering or cooling afterwards does not restore texture or reduce pungency

Stages affected: Seedling · Vegetative · Maturation

The larva of a small grey fly that tunnels into the roots of brassicas. On a root crop such as radish or turnip it ruins the part you eat, and on a young cabbage or broccoli it can kill the plant outright. It works entirely below ground, so the first sign above ground is a plant that wilts in the middle of the day and does not recover.

Visual signs

White legless maggot up to 8 mm long blunt at one end and tapering at the other found in the root or just under the skin · Brown winding tunnels through the root often with the tissue around them rotting and smelling sour · Adult a grey fly a little smaller than a housefly with dark stripes on the thorax hovering low over the soil · Outer leaves of a young plant turning bluish or purple and wilting in the middle of the day · Seedlings that fall over with the stem eaten away at and below soil level

Damage pattern

Damage is all below ground; nothing on the leaves explains it · Worst in cool wet springs and in soil rich in undecomposed organic matter · Concentrated in the first weeks after sowing or planting out · A radish or turnip can look perfect from above and be riddled inside, so cut one open rather than judging by the top · Recurs in the same bed year after year because the pupae overwinter in the soil beneath the crop

Stages affected: Seedling · Vegetative · Maturation

A soil-dwelling organism that makes brassica roots swell into distorted clubs so the plant cannot take up water. It is neither a fungus nor strictly a water mould but a plasmodiophorid, a separate single-celled lineage; what matters in practice is that fungicides do nothing against it. It is the most serious long-term disease of the cabbage family, and the reason is persistence: once a bed has it, the resting spores stay viable for up to twenty years. There is no cure, so the whole of management is keeping it out.

Visual signs

Roots swollen into distorted clubs spindles or knobbly galls instead of a normal taproot and fine roots · Above ground the plant wilts on warm afternoons and recovers overnight at first then stops recovering · Outer leaves yellowing and often taking on a red or purple cast · Stunted growth and a plant that is easy to pull because there are no working fine roots · Galls eventually going soft and rotting with a foul smell

Damage pattern

Affects only the cabbage family including radish turnip swede kale broccoli cauliflower and their weedy relatives · Appears in patches within a bed and those same patches recur and widen in later years · Worst in acidic poorly drained soil and in wet warm conditions · A root crop is unsellable and uneatable rather than merely reduced · Spread on soil carried by boots tools wheelbarrows and on the roots of bought-in transplants

Stages affected: Vegetative · Maturation

Small soft-bodied sap-sucking insects that cluster on the softest new growth. They reproduce extremely fast in warm weather and are the main insect vector of plant viruses in the garden.

Visual signs

Clusters of small pear-shaped insects on shoot tips buds and leaf undersides · A pair of short tubes (cornicles) projecting back from the rear end, which is the deciding feature · Green yellow brown red or black depending on species, wingless or winged · Curled twisted or yellowing new leaves and stunted shoots · Sticky honeydew on the leaves below, often turning black with sooty mould · White cast skins left on leaves and easily mistaken for live insects · Ants running up and down the stems

Damage pattern

Concentrated on the newest softest growth and worst on heavily fed plants · Honeydew and sooty mould appear below the colony rather than at it · Virus symptoms such as mottling yellowing and distorted growth may follow long after the aphids have gone