Flowering almond

On pome and stone fruit, brown, enlarging rot spots appear, on which concentrically arranged, grey-beige cushions of spores form. Infected fruit rot, dry out and mummify, often remaining on the tree until the next season. In spring the fungus also infects blossoms and short shoots, causing them to die back and killing the branch tips. The disease has two distinct phases. Spring blossom and twig blight (most often Monilinia laxa on stone fruit — sour cherry, sweet cherry, plum, apricot) begins on the blossoms, which turn brown, wilt and dry out without dropping; the infection enters through the stigma and style into the short shoot, girdles it and causes whole shoots to die back, with withered leaves hanging as if scorched — hence the misleading resemblance to frost damage. On stone fruit, infected shoots often exude gum (gummosis) and develop small, cracked bark cankers. The summer-to-autumn brown rot of the fruit (mainly Monilinia fructigena on apple and pear) develops on ripening fruit: the rot spot quickly engulfs the whole fruit, the flesh turns brown and softens, and characteristic, concentrically arranged rings of cream-beige cushions of conidial spores grow out on the surface. In cool conditions (including in storage), the fruit may take the form of hard, black glossy mummies lacking sporulation (so-called black rot). Mummified fruit hanging on the tree and Monilinia cankers on the shoots are the main source of spores in the following season.

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.

The fungus attacks the roots and stem base of trees and shrubs, causing their slow decline – the plants grow weakly, the crown thins, the leaves become smaller, and eventually they dry up. The diagnostic sign is white, fan-shaped sheets of fungal mycelium forming a dense layer under the bark at the stem base, with a distinct mushroom smell. In the soil and under the bark there are black or dark-brown, bootlace-like rhizomorphs, by which the fungus spreads to further plants. In autumn, clusters of fruiting bodies – honey mushrooms – grow at the base of infected trees. The above-ground symptoms are non-specific and easily confused with drought or overfeeding: some plants die suddenly (the whole tree turns brown within a single season, especially in hot weather), while others weaken over years – producing short growth, discolouring prematurely, and just before death setting an exceptionally heavy crop of flowers or fruit ('stress flowering'). In conifers, resin bleeding at the stem base is common. When the bark is exposed at the root collar, the wood of the roots and stem turns white and softly rots – honey fungus causes a white rot of the wood. The mycelial layer can be cream-coloured and leathery, spreading radially from beneath the dead bark. A biological curiosity, rather than a sign useful in garden diagnosis, is that the mycelium in moist, infected wood can glow very faintly in the dark (so-called 'cold light') – the effect is too weak and requires complete darkness, so in practice it cannot be used to identify the disease. The disease advances in foci – neighbouring plants die off one after another around an infected one.

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.

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.

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.

The caterpillars roll, fold and glue leaves together with a webbing of silk threads, creating shelters in which they feed hidden from view. When disturbed they wriggle violently backwards and drop on threads, which aids their identification; the adults are small moths with a bell-shaped outline of the folded wings. The host plants are fruit trees (apple, pear, plum), ornamental shrubs and roses. Symptoms: the caterpillars chew leaves, flower buds and fruit set and damage the skin of ripening fruit, reducing its value. The name covers many species of the family Tortricidae with a similar way of life - among them the summer fruit tortrix (Adoxophyes orana) and the rose tortrix (Archips rosana). The caterpillars are slender, up to about 1.5-2 cm long, usually light or olive green with a darker head and prothoracic plate, and very active. The moths have a wingspan of about 15-25 mm; at rest they fold the forewings roof-like, giving the characteristic bell-shaped (trapezoidal) outline, and their pattern is greyish-brown with a darker cross-band. The life cycle depends on the species: leaf-rollers overwinter as eggs laid in patches on the bark or as young caterpillars hidden in bark crevices and under bud scales; in spring they bore into the swelling buds, then move onto the leaves and fruit set, and one or two generations develop over the season. A diagnostic feature on pome fruit is the attachment of a leaf to the fruit and the shallow grazing of the skin beneath it, which leaves irregular, corky scars while the flesh deeper inside remains intact. On roses and ornamental shrubs the symptom is rolled young leaflets bound with webbing and hollowed-out buds.

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.