Garden pea

Stages affected: Vegetative · Flowering · Harvest window

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: Flowering · Harvest window

The white dusting that ends most pea rows. It thrives in exactly the weather that ends the season anyway, warm dry days with dewy nights, and spreads through a crowded row in a week. Early sowings usually crop before it arrives; late sowings rarely escape it.

Visual signs

Small white powdery spots on the upper surface of the oldest leaves that spread to coat whole leaves, stems and pods in a greyish-white felt that rubs off on a finger. Leaves beneath the coating yellow, then brown and curl. Pods are blemished and peas inside taste off. Starts low on the plant and moves up.

Damage pattern

Appears late in the crop, from flowering onward, worst on plants under drought stress, in crowded or shaded rows, and in warm dry spells with cool nights. Spreads fast across a row and to neighbouring sowings. Rarely kills before harvest on an early sowing; can take out a late sowing before it pods.

Stages affected: Seedling

A small grey-brown weevil whose adults scallop the edges of pea and bean leaves in spring while its grubs feed unseen on the nitrogen-fixing nodules below. The leaf notching looks alarming and is mostly harmless on established plants; the nodule damage is the real cost and shows as pale, slow plants on new ground.

Visual signs

Regular U-shaped notches cut from the leaf margins, giving a scalloped edge, on the lowest leaves first. Adults 4 to 5 mm, slender, grey-brown with faint pale stripes down the back and a short broad snout; they drop to the soil and play dead when the plant is touched. Grubs are legless, white with a brown head, in the soil around the roots.

Damage pattern

Notching appears on seedlings in mid spring as adults emerge from winter shelter, and again in late summer from the new generation. Heavy feeding on small seedlings in a cold spring can check them; plants past 15 cm grow through it. Below ground the grubs hollow out root nodules for about six weeks, which costs the plant nitrogen and shows as paleness rather than wilting.

Stages affected: Germination · Seedling

Soft-bodied molluscs that feed at night and in wet weather, rasping holes in leaves. Seedlings and low soft foliage are the most at risk, and a single night can take out a row of young plants.

Visual signs

Ragged holes with smooth edges chewed through the middle of leaves rather than at the margins · Silvery dried slime trails on leaves soil and pots, which is the deciding feature · Damage appears overnight and stops in dry sunny spells · Seedlings grazed off at soil level · Slugs or snails found under boards pots and mulch during the day

Damage pattern

Worst after rain irrigation and in humid shaded beds · Feeds at night; plants look untouched by day · Concentrated on low soft leaves near the soil

Stages affected: Germination

The name covers several different soil organisms doing the same thing: killing seedlings at or just below the soil line, either before they emerge or in the first fortnight after. Most of the damage in cold wet conditions comes from Pythium and Phytophthora, which are oomycetes rather than true fungi, but Rhizoctonia and Fusarium do the same job in warmer soil. The organisms are present in almost every garden soil and most reused potting mix; what turns them from harmless to lethal is cold, wet, airless conditions and a seedling that takes too long to get up. Utah State names it as one of the three problems on cilantro, which is a slow germinator sown into cool spring soil.

Visual signs

Seedlings that were upright yesterday lying flat this morning, still green · A dark water-soaked pinch in the stem right at soil level, thinner than the stem above and below it · Seedlings that never emerge at all, with the seed soft and brown when you dig one up · A bare patch in an otherwise even row, often roughly circular and spreading outward day by day · Sometimes a fine grey or white web on the soil surface in the affected patch · Roots brown and stringy, with the outer layer sliding off the core when pulled between finger and thumb

Damage pattern

Spreads outward from a centre, so an expanding bare patch rather than scattered single losses. It is a seedling disease and stops mattering once the stem has woody tissue at the base, usually two to three weeks after emergence. A sowing that fails patchily and never recovers, where digging finds soft brown seed, is usually this rather than poor seed.

Stages affected: Seedling · Vegetative · Flowering

A complex of soil organisms, a true fungus (Fusarium) and two water moulds (Aphanomyces and Pythium), that rot pea roots in cold wet or warm wet soil and cannot be told apart from above ground. It is the reason peas fail in a bed that grew them too often or lies wet, and the organisms persist for years once established.

Visual signs

Plants stunted and yellowing from the lowest leaves upward, often in patches that follow the wettest part of the bed. Pull a plant: the roots and the stem below soil are brown to black, soft, with the outer layer sloughing off, and few or no healthy pink nodules. Aphanomyces gives a honey-brown, water-soaked root; Fusarium a red-brown streaking inside the stem base.

Damage pattern

Shows from three to four weeks after sowing, worst where soil was saturated after sowing or in a warm wet spell later. Plants may struggle on and set a poor crop or collapse at flowering when demand on the roots peaks. Patches enlarge year on year in a bed that grows peas without a break.

Stages affected: Seedling

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