Sweet pepper

Stages affected: Fruiting · Harvest window

Not a disease. Sunburn on fruit that has lost the leaf cover shading it — a pale sunken papery patch on the side facing the afternoon sun, which then often rots where soft fungi move into the dead tissue. It is nearly always self-inflicted, by pruning a crop that should not be pruned or by stripping leaves after a disease has already thinned the canopy.

Visual signs

A pale whitish or tan patch on the side of the fruit that faces the sun, never on the shaded side · The patch is sunken dry and papery with a distinct edge and feels thinner than the flesh around it · On peppers it goes white to tan; on tomatoes yellow to white; on squash a hard bleached scar · Black or grey mould often growing on the dead patch afterwards, which is a secondary coloniser rather than the cause · Leaves above the affected fruit missing, wilted or stripped

Damage pattern

Only ever on the exposed sunlit side of a fruit, which is what settles the diagnosis · Appears within days of a canopy being opened up, whether by pruning by wilting or by leaf disease · Worst on the outside of a row and on the south or west face of a plant · Follows a hot bright spell, often the first one after the leaves were removed · Never spreads from fruit to fruit and never affects shaded fruit on the same plant

Stages affected: Vegetative · Flowering · Fruiting · Harvest window

A seed-borne bacterium that spots the leaves and scabs the fruit of peppers and tomatoes. On pepper it is the more damaging of the two, because a spotted fruit is unsellable and unappetising and heavy leaf loss exposes the rest of the crop to sunscald. Nothing cures it, so it is managed by clean seed, rotation and keeping out of the bed while the foliage is wet.

Visual signs

Small water-soaked spots on leaves that turn brown to black with a narrow yellow border · Spots often angular where they run up against a vein · Raised scabby spots on the fruit, rough to the touch, sometimes cracked in the centre · Heavy spotting running together and the leaf yellowing and dropping · Worst on the lower and inner leaves first then spreading upward

Damage pattern

Advances in steps after rain or overhead watering rather than steadily · Spreads along a row in the direction hands tools and water have travelled · Defoliation is the real damage on pepper, because the exposed fruit then sunscalds · Fruit spots make the crop unusable rather than merely marked · Recurs from saved seed and from debris left in the bed

Stages affected: Seedling · Vegetative · Flowering

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

Stages affected: Vegetative · Flowering · Fruiting

A large green caterpillar, the larva of a hawk moth, that feeds on the leaves flowers and fruit of tomato and its relatives. The tobacco hornworm is an equally common close relative and is managed identically.

Visual signs

Green caterpillar up to 100 mm long with a horn at the tail end · Tomato hornworm has eight chevron-shaped white stripes on each side; tobacco hornworm has seven diagonal stripes · Dark green to black droppings the size of rice grains on leaves and on the ground below · Stems chewed bare to the ribs and large deep cavities gouged in green fruit · White rice-like cocoons standing up on a caterpillar back mean parasitic wasps have already killed it

Damage pattern

Defoliation from the top of the plant downward and often one branch at a time · Droppings appear before the caterpillar is spotted; look on the stem directly above them · Feeding cavities in fruit are larger and deeper than armyworm damage

Stages affected: Seedling · Vegetative · At planting

The caterpillars of several drab night-flying moths. They live at the soil surface and chew through the stems of young plants at ground level, so you almost always find the damage before you find the caterpillar.

Visual signs

Smooth dull caterpillar up to 40 mm long in grey brown or near black often with faint stripes · Curls tightly into a C shape the moment it is touched or uncovered · Found 25 to 50 mm down in loose soil within a hand's width of the damaged plant · Nothing visible on the plants by day because they feed after dark

Damage pattern

A young plant cut clean through at soil level and left lying beside its own stump · Whole seedlings gone overnight with the root still in the ground · Ragged holes chewed in the leaves that rest on the soil · Damage running along a stretch of row rather than scattered across the bed

Stages affected: 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: Fruiting · Harvest window

Not an infection but a disorder: a firm dark patch at the base of the fruit caused by calcium failing to reach the fruit as it grows, almost always because soil moisture swung between wet and dry. Tomato pepper aubergine and squash all get it.

Visual signs

A water-soaked spot at the blossom end (the bottom) of the fruit opposite the stem · The spot enlarges and turns brown to black, flat and leathery rather than soft and mushy · The lesion stays firm and dry unless other rots move in afterwards · Affects the earliest and largest fruits first and often only some fruit on a truss · Leaves and stems look completely healthy

Damage pattern

Follows a dry spell a heatwave or erratic watering two to three weeks earlier · Common in containers and in fast-draining sandy soil · Worse where nitrogen has been applied heavily