Grapevine

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.

Yellow or angular (vein-bounded) spots on the upper leaf surface, matched underneath by a grey-violet or brown coating of spores. It differs from powdery mildew, whose white coating sits on the upper surface. It develops in humidity and cool nights and is dangerous to cucumbers, onions and grapevines. The spots are initially light green or yellowing, and their angular, mosaic-like shape arises because the pathogen's spread is halted by the larger leaf veins. The delicate, felt-like coating on the underside (hence the name 'mildew') is the sporulation of the oomycete — best seen in the morning or after a period of high air humidity. Over time the spots turn brown, dry out and merge, the leaf dies prematurely, which weakens the whole plant and lowers the yield. The disease is highly host-specialised: cucumbers and squashes are attacked by Pseudoperonospora cubensis, onion by Peronospora destructor, grapevine by Plasmopara viticola, and lettuce by Bremia lactucae — so infection of one species usually does not spread to unrelated crops.

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.

A soft scale whose females form brown, dome-shaped, strongly convex "cups" (3–6 mm) sitting motionless on shoots, twigs and leaf bases. They suck sap, weakening the plants, and excrete abundant honeydew on which black sooty mould develops, disfiguring leaves and fruit. It feeds on fruit trees (plum, peach), grapevine, ornamental shrubs and houseplants. It belongs to the soft scales (Coccidae), not to the true armoured scales — its brown shield is the sclerotized body of the female and cannot be separated from her. In the Polish climate it usually develops one generation per year. It overwinters as an immature larva (second instar) attached to shoots and twigs, in bark crevices and near the buds. In spring the larvae resume feeding and the females grow quickly, turning into the characteristic, hardening "cups". Beneath its shield the mature female lays numerous eggs — often from several hundred to over a thousand. The crawling larvae (so-called crawlers) that hatch from them, usually at the turn of June and July, spread out onto the leaves and young shoots, where they attach and feed; before leaf fall they return to the shoots to overwinter. Symptoms of infestation are weakened growth and dieback of twigs under heavy attack, sticky, glossy honeydew on the leaves and beneath the plant, a black sooty coating that hampers photosynthesis, and numerous ants feeding on the honeydew. The larvae and females cluster in the forks of twigs, on the undersides of shoots, at the base of the leaves and along the veins and leaf stalks.

Small (2-10 mm), elongated true bugs, usually greenish or yellowish, which when disturbed nimbly jump and scurry sideways across the leaf. They suck sap mainly from the underside of leaves, causing fine pale stippling, discolouration and mottling of the blade. Many species are vectors of phytoplasmas and viruses, so the damage can be more serious than the feeding itself. They feed on perennials, vegetables, grapevine and ornamentals. The body is wedge-shaped, tapering towards the rear, and the wings are held roof-like over the abdomen at rest; the characteristic oblique, sideways gait and the ability to make long leaps are what give the group its name. The larvae (nymphs) are wingless, paler and smaller than the adults, cling to the leaf underside and also move sideways; they pass through several moults, and the white, transparent cast skins they leave stuck to the underside of the blade are one of the more reliable signs that leafhoppers are present. The feeding symptoms result from the emptying of mesophyll cells: fine, pale flecking appears first, then merges into marbled pale patches, and in some species (e.g. leafhoppers of the genus Empoasca) the leaf margins yellow, brown and curl, a condition known as hopperburn. Unlike aphids, leafhoppers usually do not coat the plant with abundant honeydew, so sooty moulds rarely develop with them. The eggs are laid singly into slits cut in the tissue - into veins, leaf stalks or young shoots; many species overwinter as eggs, some as adults in leaf litter or on evergreen plants, and one to several generations develop over the season. Their role as vectors is, however, the most important: leafhoppers transmit, among others, phytoplasmas (aster-type yellows - carried by leafhoppers of the genus Macrosteles, and on grapevine the golden yellows, flavescence doree, carried by the leafhopper Scaphoideus titanus) and viruses, so that even a small population can be dangerous in crops susceptible to these diseases.