Garden strawberry

A white, powdery coating on leaves, shoots and buds. The leaves turn yellow, become deformed and drop prematurely. The coating develops on both sides of the leaf blade, is often clearly visible from above, and can easily be rubbed off with a finger — it is the superficial mycelium of an ectoparasite that draws nutrients from the epidermal cells by means of feeding structures (haustoria). At first single, round, white spots appear, which in time merge and cover the entire leaf surface and the young growth. Young leaves and the current season's shoots are the most susceptible; heavy infection causes them to pucker, stiffen and stop growing, and on buds it leads to deformation or death of the flowers. On the fruit of some species (gooseberry, apple, cucurbits) the coating leaves russeting or a corky skin. Towards the end of the season, small, dark fruiting bodies (chasmothecia, formerly called cleistothecia) — the pathogen's overwintering structures — appear within the coating. The disease affects many plants, including roses, oak, privet, lilac, cucurbits, cereals, grapevine, apple, gooseberry, phlox and coneflowers, with each of these hosts being infected by a specialised species of fungus.

A grey-brown, fluffy coating of mycelium on flowers, fruit, leaves and shoots, preceded by watery, rotting spots. It attacks weakened and damaged tissue and develops rapidly in humidity and cool conditions and where air circulation is poor. Common on strawberries, begonias, peonies and roses. The coating is characteristically 'mousy' — fluffy and ashy grey, and when the infected tissue is knocked a visible cloud of spores (conidia) puffs up, which is a diagnostic feature of this disease. Infection usually starts in the weakest tissues: fading petals, wounds, hail marks or pest feeding damage, as well as pollen residue settled on the petals. Small, brown, watery spots appear on the flowers and quickly engulf the whole bloom ('flower blight'); from the infected flower the fungus often grows down into the shoot, causing it to constrict and die back. On soft fruit (strawberry, raspberry, grapes, tomato) a watery, browning rot develops, covered with a thick layer of grey, fluffy felt — the berry softens and 'dissolves'. On seedlings and cuttings Botrytis causes basal stem rot and the sudden collapse of plants. In older, dying mycelium and on plant debris hard, black, irregular lumps form — sclerotia (resting bodies), by which the pathogen overwinters in the soil and in plant debris. The disease also shows up after harvest, as a rapidly advancing storage rot of fruit and vegetables.

Numerous small, round spots appear on the leaves with a lighter, greyish centre and a darker, brown margin. Within the spots tiny black dots are visible – pycnidia, the fruiting bodies of the fungus, which distinguishes this disease from other leaf spots. The infection progresses from the lower, oldest leaves upwards; with heavy infection the spots merge, the leaves yellow, dry out and drop prematurely, weakening the plant. Affected plants include tomato, currant, phlox and many perennials. The spots are usually 2–5 mm across; the decisive identifying sign is the dark pycnidia at their centre – best seen through a hand lens, and in high humidity exuding whitish 'tendrils' of spores. Leaves densely peppered with spots look as if dusted. The disease is favoured by warm (about 20–25°C), humid weather and water lingering on the leaves for a long time (rain, dew, overhead watering). On tomato the infection is confined almost exclusively to the leaves and leaf stalks – the fruit usually stays healthy – but the loss of the photosynthetic apparatus leads to smaller fruit and exposes it to sunscald.

Small (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.

Slugs and shelled snails that feed at night and after rain. Symptoms: irregular holes in the leaves and young seedlings eaten off completely, silvery slime trails on leaves and soil. The greatest damage occurs in damp, shaded spots — particularly on lettuce, strawberries and hostas. The most damaging in gardens are the slugs (which lack an external shell): the Spanish slug (Arion vulgaris, formerly described as A. lusitanicus) and the grey field slug (Deroceras reticulatum). The leopard slug (Limax maximus) can be morphologically similar to them, but it feeds mainly on decaying organic matter and fungi and may even prey on other slugs, so it is of little importance as a pest of living plants. Shelled forms — grove snails (Cepaea) or the protected Roman snail (Helix pomatia) — usually cause less damage. The body is soft, elongated and permanently covered in slime; on the head there are two pairs of retractable tentacles — the longer upper pair bears the eyes, the shorter lower pair serves a tactile and olfactory function. Slugs and snails are hermaphrodites: they lay spherical, transparent or pearly eggs in clusters, hidden in damp soil, under stones and in leaf litter. A single Spanish slug can lay several hundred eggs; both eggs and young slugs overwinter, and feeding lasts from spring to late autumn, intensifying on warm, damp nights. The damage has smooth edges and often appears in the middle of the leaf blade, not only from the margin; seedlings and transplants are sometimes eaten down to bare soil, and on strawberries and ripening vegetables the slugs gnaw hollows into the fruit. The decisive diagnostic sign is the dried, silvery glistening slime trail — no insect leaves one.

Weevils 8-12 mm long, black or dark brown, with a short, broad snout, flightless and active at night. Their larvae are white, legless, C-shaped, with a brown head, and live in the soil. Symptoms: the adult beetles notch characteristic semicircular bites into leaf margins at night (box, rhododendron, bergenia, strawberry, houseplants), while the larvae gnaw at roots, bulbs and the base of shoots, causing the plant to wilt suddenly and die. The most common is the black vine weevil (Otiorhynchus sulcatus), more rarely the strawberry root weevil (O. ovatus) and related species. A key factor behind their numbers is parthenogenetic reproduction (virgin birth): populations consist almost exclusively of females, and a single female lays several hundred eggs into the soil without a male, so an outbreak builds up quickly. Life cycle: the beetles overwinter mainly as larvae (some as adults) in the soil; the adults emerge in late spring and early summer and for about 3-4 weeks carry out maturation feeding on the leaves before they begin to lay eggs, while the larvae feed on roots from summer through autumn and again in early spring. The larval stage is the most dangerous - the larvae chew the roots and gnaw the root collar at the base of the shoot (girdling), causing the plant to wilt suddenly despite moist soil and to lift easily out of the substrate; adult feeding (semicircular notches on leaf margins) mainly disfigures the plant and rarely kills it. Plants in containers are particularly at risk, where the limited root ball is quickly destroyed. The beetles are flightless, so they spread by walking across the substrate and - above all - with infested plants and substrate, which makes newly bought potted plants the main route of introduction.

Large, fleshy larvae of cockchafers (common and forest cockchafer), growing to 4-6 cm, cream-white and C-shaped, with a brown head, three pairs of legs and a darker, translucent tip to the abdomen. They develop in the soil for 3-4 years. Symptoms: gnawed roots, tubers and bulbs, wilting and yellowing plants that lift easily from the soil (roots chewed off), and patchy dieback of lawns and seedlings. The full cycle lasts 3-4 years: the beetles emerge during the May-June flight, the females lay their eggs in the soil, readily beneath dense turf and along field margins, and the hatched larvae pass through three developmental stages. The youngest grubs feed on fine rootlets and cause little damage, whereas larvae in their second and third year, when they are largest, gnaw thick roots, tubers and underground plant parts, causing the characteristic patchy loss of lawn and seedlings; the damaged sward can then be rolled up like a carpet because it has been stripped of roots. White grubs gather in nests, so damage appears in focal patches rather than evenly across the whole area. Cockchafer larvae are sometimes confused with the grubs of the rose chafer (Cetonia aurata) - these, however, are beneficial, breaking down dead organic matter in compost and humus, have a distinctly smaller head and fine legs and, when placed on a flat surface, move on their backs; they should not be destroyed.

Microscopic roundworms (0.3–2 mm), invisible to the naked eye, feeding inside the roots. The diagnostic sign is the characteristic knotty swellings (galls) on the roots, formed in response to larval secretions. Affected plants grow weakly, wilt on hot days despite moist soil, turn yellow and yield poorly. Most damaging under cover (tomato, cucumber) and on carrot, lettuce, strawberry and houseplants. The mobile, infective stage is the invasive larvae (second-stage juveniles, J2) present in the soil: they penetrate the young root tips just behind the apex and induce the formation of specialised feeding cells (giant cells). The female feeding there swells into a pear shape, stays inside the root and lays hundreds of eggs in a gelatinous sac that often protrudes onto the surface of the gall. Warmth speeds up development — the optimum soil temperature is about 25–30°C, which is why in tunnels and greenhouses, and in light, quickly drying sandy soils, the nematode produces several generations per season and does the most damage. On tomato and cucumber the galls are spindle-shaped thickenings fused with the root, giving it a beaded, knotty form; they cannot be rubbed off with the fingers — this distinguishes them from the beneficial nodules of nitrogen-fixing bacteria on the roots of legumes. On carrot, parsley and parsnip the feeding causes forking, shortening and hairiness of the storage root, which lowers its market quality even without obvious galls. The above-ground symptoms — stunting, wilting during the hottest hours despite moist soil, chlorosis and nutrient-deficiency signs — result from damage to the root system, which no longer takes up water or mineral salts; in the field the weakened plants occur in patches (nests). The pest spreads with infested soil, run-off water, on tools and footwear, and above all with infected seedlings and cuttings; in the soil it survives as eggs for many months, even without a host.

Tiny (0.3–0.5 mm) arachnids, hard to spot with the naked eye, feeding on the underside of leaves. Symptoms: fine, pale speckling (feeding punctures); over time the leaves turn grey, yellow and dry out. Under heavy infestation a fine webbing becomes visible. Warm, dry air favours their development — a common problem for houseplants in winter near radiators. Spider mites are not insects but mites of the family Tetranychidae — adults have 8 legs (larvae only 6). The most common in cultivation is the two-spotted spider mite (Tetranychus urticae): yellowish-green females carry two dark spots on the sides of the body, while overwintering females turn orange-red. In orchards the fruit tree red spider mite (Panonychus ulmi) is frequent, whose red eggs overwinter in clusters on the bark of the shoots. Feeding mechanism: the mites puncture the cells of the epidermis and mesophyll on the underside of the leaf and suck out their contents, and the emptied cells fill with air — hence the characteristic, silvery-grey, fine speckling visible from the upper side of the blade (resembling a mosaic discolouration). At high numbers the leaves turn brown, curl and drop prematurely, and the whole plant weakens and loses its growth. Dense webbing spun between the leaves and shoot tips appears only under an advanced attack and is a sign of the risk of the pest spreading to neighbouring plants. The development cycle is very fast in warmth and drought — at a temperature of 25–30°C a single generation can be completed in 1–2 weeks, hence the numerous generations per season and the rapid, exponential build-up of the population. Females lay spherical, transparent eggs on the underside of the leaves. Fertilised females overwinter (in bark crevices, leaf litter and plant debris) or — in the fruit tree red spider mite — the eggs on the bark. Early infestation is easy to miss; diagnosis is helped by shaking a leaf over a white sheet of paper (moving specks become visible) or examining the underside of the leaf with a magnifying glass.