Cherry laurel

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.

Sunken, necrotic wounds (cankers) form on the trunk and branches, from which – especially in spring – amber gum oozes (gummosis). The bark over the wounds dies and cracks, and infected buds and short shoots fail to break or die in spring, so whole sections of the crown dry out. Small, brown, watery spots may appear on the leaves and fall out of the blade ('shot-hole'). The disease affects stone-fruit trees – sour cherry, sweet cherry, plum, peach and apricot – and when it girdles a branch it kills it. The cause is two bacterial pathovars — Pseudomonas syringae pv. syringae and pv. morsprunorum — with similar symptoms that cannot be told apart with the naked eye. A characteristic early symptom is the dying of buds and flowers in spring (so-called blossom blast): buds turn brown and fail to open, and individual branches suddenly wilt and dry out, holding their browned leaves for a long time. The gum oozing from the cankers is glassy to amber and appears most abundantly in spring and early summer, after the sap starts to flow; in high summer the ooze usually stops. When the bark is cut at the edge of a canker, the tissue beneath is often watery, rusty-brown, with a sour, fermenting smell (typical of pv. syringae). The leaf spots are at first small, angular, watery and surrounded by a lighter halo; their dead centres crumble away, producing a 'shot-hole' effect. The symptoms are easily confused with frost damage to the bark and with fungal shoot dieback (brown rot) and fungal shot-hole of the leaves (Wilsonomyces carpophilus) — the key then is the season of peak activity and the presence of fungal sporulation. The disease intensifies in cool, wet weather in spring and autumn; in summer, in warmth and drought, the bacterium is least active.

Immobile, brown or yellowish shields (1-4 mm) attached to stems and the underside of leaves, especially along the veins. Easily mistaken for growths on the plant. They suck sap, causing yellowing and weakening, and excrete sticky honeydew. Common on figs, orchids and plants with tough leaves. The collective name covers two groups with different biology. Armoured scales (Diaspididae) have a hard waxy shield separate from the body, which can be prised off - beneath it emerges a tiny, legless and wingless female; they do not excrete honeydew. Soft scales (Coccidae) have a convex, cup-shaped cover fused with the body, and it is they that excrete it abundantly. Sticky honeydew - the domain of soft scales and other honeydew-producing scale insects, not of armoured scales - settles on the leaves and attracts sooty mould fungi (sooty mould, sooty blotch) as well as ants, which defend the colony against predators. The only mobile feeding stage is the crawler - a flat, tiny larva which, after hatching from beneath the mother's shield, disperses over the plant, then settles, inserts its stylet into the conducting tissues and loses the ability to move; adult females remain immobile for the rest of their lives. Males pupate and, as tiny, winged, short-lived insects, do not feed. In heated interiors the pest breeds all year round, producing several overlapping generations; outdoors usually 1-3 generations, and fertilised females or eggs hidden beneath the shield overwinter. Feeding symptoms are yellowing and premature leaf drop, dieback of shoots, stunting and weakening of the plant, and secondarily a black coating of sooty mould on leaves covered with honeydew. On fruit trees infested by San Jose scale (Comstockaspis perniciosa), reddish discolouration appears around the feeding sites, and heavily colonised branches die back. Because the shields are immobile and their colour blends into the bark and veins, an infestation is easily overlooked until honeydew appears or the plant is noticeably weakened - which is why regular inspection of the leaf undersides and shoot axils is key.

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.