Rosemary

Stages affected: Dormant · At planting

Soil-borne water moulds that rot the roots and crown of plants growing in soil that stays saturated: fruit and nut trees, strawberries (where one species causes red stele), raspberries, peppers and many ornamentals. They need free water to swim to the roots, so this is a drainage and watering disease above all. Once the crown is rotted there is no cure; everything is prevention.

Visual signs

Plants that stay small, wilt in the first warm days although the soil is wet, and yellow or redden early, often on one side first · On strawberries, roots with few side roots and a red core when split lengthways (red stele), or a brown, rotted crown when the plant is cut through · On trees, leaves undersized and dropping early, twigs dying back, and a brown or reddish stain or canker in the wood when the bark is cut away at the base of the trunk · Feeder roots dark brown and brittle on any host · Often follows a wet winter, a blocked drain, or a dripper placed against the stem or trunk

Damage pattern

Concentrated in low spots, heavy soil and anywhere water stands after rain; spreads downhill and along the row with drainage water · Worse where soil or mulch is piled against the stem or trunk · On strawberries shows in the first warm spell of spring on plants that looked fine in winter; on trees builds over a season or two · Susceptibility varies widely by variety and rootstock, which is the main lever where the disease is known

Stages affected: Vegetative · Dormant

Mites under 1.3 mm that feed on the undersides of leaves and spin fine webbing. Populations explode in hot dusty dry conditions and after broad-spectrum sprays kill their predators.

Visual signs

Fine pale stippling on leaves seen best held up to the light · Fine silk webbing on leaf undersides and later on twigs and nuts · Leaves turning yellowish or bronzed then dropping in mid to late summer · Moving specks on the leaf underside visible with a hand lens

Damage pattern

Starts on the dusty side of the tree near paths and drives · Worst on water-stressed trees in hot weather · Late-summer leaf loss costs little this season but reduces next year crop

Stages affected: Dormant

Small soft-bodied sap-sucking insects coated in white, cottony wax. A pest of plants kept or overwintered indoors and in greenhouses: rosemary, citrus, coleus, jade, cacti and many houseplants. They usually arrive on a new plant or on one brought in from outside for the winter.

Visual signs

Oval, segmented, pinkish insects about 1.5 mm long under a white mealy coating, often with short waxy filaments round the edge, packed into leaf joints, stem crotches and leaf undersides. Cottony egg masses look like tufts of cotton wool. Leaves below are sticky with honeydew and may blacken with sooty mould.

Damage pattern

Feeding weakens and stunts the plant and causes yellowing, leaf drop and wilting; flower buds drop before opening. Numbers build fast indoors with no winter to stop them, two to six generations a year, and they hide in tight places, under unglazed pot rims and saucers.

Stages affected: Dormant

The soft grey fuzz that turns ripe strawberries, raspberries, grapes and tomatoes to mush within a day of warm wet weather, and rots the crowded centres of low herbs such as thyme. One fungus with hundreds of hosts, living on dead plant material everywhere; on fruit it infects the flowers at bloom and waits in the green fruit until it ripens. Wet tissue, crowded plants and overripe or damaged growth are what it needs.

Visual signs

On ripening fruit, a light brown soft rot, usually starting at the calyx end or where a berry touches the soil or another berry, quickly covered in a dense grey-brown velvety fuzz that puffs spores when touched. Dead brown flowers and flower stalks earlier in the season. On leaves and stems, brown water-soaked patches that grow the same grey fuzz in humid weather.

Damage pattern

Explodes in warm, humid or rainy weather during bloom and harvest, 15 to 25 °C with fruit wet for many hours; one rotting berry infects all the berries touching it. Worst in dense, overfed plantings, under heavy overhead watering, and where ripe fruit is left unpicked. Continues in the fridge after picking.

Stages affected: Dormant

A white, talcum-like coating on leaves and stems caused by many closely related fungi, each with a narrow host range: the mildew on one plant rarely spreads to an unrelated one nearby. On herbs such as dill and rosemary and on many flowers it is mostly cosmetic, but heavy infections yellow and drop leaves. The crop-specific mildews of cucurbits and peas have their own records.

Visual signs

Greyish-white powdery patches on the upper leaf surface, stems and flowers that can be rubbed off with a finger, spreading to cover whole leaves. Leaves may curl or twist first, then yellow and brown; flowers may fail to open. Late in the season tiny dark specks can form in the white growth.

Damage pattern

Starts on crowded, shaded or overwatered plants and on soft growth from heavy nitrogen feeding. Worst when days are mild and nights humid, active once days pass about 16 °C and less common in summer heat. Indoors, still air and poor light on overwintered herbs bring it on.

Stages affected: Vegetative · Dormant

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