Common pear

Olive-green, velvety, blurred spots appear on the leaves and gradually darken and turn brown; heavily infected leaves turn yellow and drop prematurely. Dark, corky spots form on the fruit and crack as the fruit grows, producing the characteristic fissures and deformations. Infected fruit stay small, store poorly and lose market value. The first spots are usually seen on the youngest, developing leaves and on the sepals of the flowers; at first they are poorly delimited, later taking on a distinctly dark-olive to blackish-brown colour with a velvety sporulating coating. The primary spring infections are caused by ascospores discharged during rain from the fruiting bodies overwintering in the fallen leaves; the resulting spots in turn produce conidia responsible for numerous secondary infections through the summer. Early infection of the fruitlets leads to one-sided growth and severe fruit deformation, and the cracks in the corky tissue become entry points for rot fungi and storage rots. On especially susceptible cultivars the disease also produces crusty lesions and cracks on the young shoots and twigs, which become an additional source of spores the following season. A separate form is the so-called storage scab - small, pinpoint spots that only show up in cold storage when the fruit was infected just before harvest.

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.

Blossoms and young shoots suddenly turn brown and then black, looking as if scorched by fire — hence the name of the disease. The tips of infected shoots bend downwards into a characteristic hook resembling a shepherd's crook. In humid conditions a milky, sticky bacterial ooze seeps from the infected tissue, and the infection spreads rapidly down the shoot, killing whole branches. Infected leaves and fruit dry out but remain attached to the tree for a long time. Pear and quince are the most severely affected, followed by apple, and among ornamental and wild plants — hawthorn, cotoneaster, firethorn (Pyracantha) and rowan, which can be a dangerous reservoir of infection. On the bark of the branches and trunk, sharply delimited, sunken necroses (bark canker) form with cracking bark; when the bark is cut, the tissue beneath is discoloured reddish-brown, often with marbled streaks. The drop of bacterial ooze eventually turns amber and dries, and the presence of the bacterium can be confirmed by the so-called streaming test — from freshly cut infected tissue immersed in water, threads of a cloudy bacterial suspension flow out. Infected fruit turns black and mummifies, remaining on the tree, which distinguishes fire blight from ordinary wilting caused by water shortage.

The disease has a two-host cycle: the pear is the main host, while juniper — especially savin and Chinese juniper, on which the fungus overwinters — is the alternate host. In spring, bright orange-red spots appear on the upper surface of pear leaves and gradually enlarge. In summer, warty, sieve-like outgrowths (aecia) that release spores develop on the underside of the leaves, opposite the spots. On juniper the fungus forms spindle-shaped swellings on the shoots, which in spring swell into gelatinous, orange outgrowths in wet weather. The spots on the upper leaf surface are initially small and yellow-green, later turning a bright orange-red with a reddish rim; at their centre, on the upper side, tiny black dots (spermogonia) are sometimes visible. The corresponding aecia on the underside take the form of light-brown, tube-like sieve-shaped outgrowths a few millimetres long, gathered in clusters — it is precisely this lattice-like arrangement that gave the disease its German name 'Birnengitterrost' (pear lattice rust). Under heavy infection there are many spots, the leaves yellow and drop prematurely, the tree weakens and yields less; occasionally spots also appear on the leaf stalks, young shoots and fruit. The cycle is strictly one-directional: in spring, in wet weather, the gelatinous outgrowths on juniper release basidiospores carried by the wind even hundreds of metres, which infect only the pear — the fungus does not spread from pear to pear, while the mature aecia on pear leaves in turn release spores that infect the juniper again, not other pears.

The disease mainly attacks apple and pear. Sunken, concentrically cracked and gradually enlarging wounds, known as cankers, form on the shoots and branches, and within them the bark and wood die back. Around the wound the tree produces ridges of callus tissue in an attempt to heal it over. In autumn and on damp days, small, brick-red fruiting bodies of the fungus appear along the edges of the cankers. Branches above the canker die back, while young shoots become infected through the leaf scars and quickly perish. A canker is a perennial wound — the fungus overwinters in the infected bark and each year widens the margin of necrosis, so that the edges of the wound form characteristic concentric rings that alternate between dying tissue and ridges of callus (an image resembling a 'target'). The fungus produces two types of spores: in summer, in moist conditions, creamy-white, slimy cushions of conidial spores appear on the surface of the canker, while in autumn and winter the aforementioned brick-red, spherical fruiting bodies (perithecia) with ascospores form. Infection occurs mainly through injuries and natural points of entry: fresh scars left by fallen leaves, stipular scars and lenticels, as well as wounds from pruning and fruit picking, frost cracks and damage from woolly apple aphid feeding. A shoot or branch completely girdled by a canker dies back above the wound. The same fungus can also cause fruit rot — most often developing from the calyx end and only becoming apparent in storage.

A nocturnal moth with a wingspan of 15-20 mm; the forewings are grey-brown with a characteristic coppery, glossy patch at the tip. The caterpillar is whitish to pinkish with a brown head, grows to about 18 mm and tunnels right into the core of an apple or pear (less often quince or walnut). Symptoms: 'maggoty' fruit, entry holes with brown, sawdust-like droppings, and premature fruit drop. The caterpillar has five pairs of abdominal prolegs - the key feature distinguishing it from the larva of the apple sawfly, which has six or more. The codling moth overwinters as a full-grown caterpillar in a dense cocoon hidden in bark crevices, under loose flakes of bark, in the soil at the base of the trunk or in fruit crates; in spring it pupates, and the moths usually emerge from the end of apple blossom (May-June). Flights take place at dusk and at night, when the air temperature rises above about 15C. Females lay eggs singly on the fruit and on leaves nearby; after about one to two weeks the caterpillars hatch and, after a short wandering, bore into the fruit and head for the seed cavity, feeding on the flesh and the seeds. Under Polish conditions there is usually one full generation, and in warmer years and in the south of the country a partial second one whose feeding reaches harvest. Damaged fruit rots, drops prematurely and is unfit for storage.

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.

Small sucking insects whose adults resemble tiny cicadas and jump off the shoots when disturbed. The flat, yellowish nymphs feed on the shoots, leaves and fruit of the pear, excreting abundant sticky honeydew. Sooty mould develops on the honeydew, coating and blackening the leaves, shoots and fruit, weakening the plant and leaving the fruit deformed and soiled. The pear psylla is also a vector of the dangerous pear decline (phytoplasma), which makes it particularly harmful. The adults are 2.5-3 mm long with roof-like folded wings, and they occur in two seasonal forms - a larger, dark (brownish-black) winter form that overwinters, and a smaller, paler yellow-green summer form that develops in the warmer months. The eggs are small and elongate, at first yellowish then orange, laid in chains along the shoots, at the base of the buds and on the spurs. The newly hatched nymphs are flattened and oval, sitting in a droplet of their own honeydew, darkening with age and developing wing buds. Several overlapping generations (usually 3-5) develop over the season. The insect overwinters as the adult winter form in bark crevices, under flaking bark and in the leaf litter in the orchard and its surroundings; the females lay their first eggs very early, before budburst, on the bare shoots. Under heavy infestation the leaves drop prematurely, growth is weak, and the fruit is russeted and soiled by the sooty mould.

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.

A small beetle of the weevil family, about 4–5 mm long, brown-grey, with a pale, oblique V-shaped band on the wing cases and a long, curved snout. In early spring, before flowering, the females lay single eggs inside the developing flower buds; the hatched legless larva eats out the inside of the bud, which stops developing, turns brown and dries up, remaining closed as if "scorched" — this is the most conspicuous symptom. It feeds on apple and pear; under heavy pressure it can destroy a considerable part of the flower buds. The main and proper host is the apple — on pear, comparable bud damage is caused above all by other, closely related blossom-weevil species (among them the pear blossom weevil, Anthonomus piri), so infestation of pears can only occasionally be attributed to this species. The species produces one generation per year. The adult beetles overwinter in bark crevices, under lifting flakes of bark, in leaf litter and at the base of the trunks; in early spring, once the temperature rises above a few degrees (roughly at the bud-swelling and green-bud stage), they leave their hiding places and move up into the crowns. As they feed, they pierce the swelling buds with their snout, and droplets of sap flow out — a symptom known as "bud weeping." The female bores a hole in a flower bud with its snout and lays a single egg inside it. The larva develops in concealment, eating out the stamens and pistil, then pupates inside the browned, undeveloped bud — the dried petals form a characteristic brown "cap" over it. The young beetles of the new generation emerge at the turn of spring and summer, feed briefly on the leaves, and then withdraw to their shelters for summer dormancy and overwintering. The harmfulness depends strongly on the abundance of flowering: in years of lush flowering, the destruction of some buds acts like natural thinning and may be immaterial to the yield, whereas with weak flowering the loss of fruit set is severe.

A moth with marked sexual dimorphism: the male has grey-brown, finely banded wings with a span of about 25 mm, whereas the female is practically wingless and flightless and therefore climbs up the trunk in autumn to lay its eggs in the crown. In spring green looper caterpillars with pale lengthwise stripes hatch, moving with the characteristic "looping" gait (arching the rear of the body) and eating the developing buds, young leaves and fruitlets, often webbing them together with threads. It feeds on apple, pear, plum, cherry and many deciduous trees and shrubs. The mature caterpillar reaches about 25 mm in length and is yellow-green with a darker dorsal line and pale stripes along its sides; as a typical looper (Geometridae) it has only two pairs of prolegs at the end of the abdomen, hence its looping gait. The eggs are laid singly near the buds and in bark crevices, where they overwinter, and just before the spring hatch they change colour from greenish to orange-red. The species has one generation a year: the moths fly in late autumn (October-December, which is the origin of the Polish name "przedzimek", meaning before-winter), on cool, frost-free evenings, and the flightless females then climb the trunks. The spring hatch of the caterpillars is closely synchronised with bud burst (usually April); after about 4-6 weeks of feeding the caterpillars lower themselves to the ground on threads and pupate shallowly in the soil, where the pupa spends the summer. The signs of feeding are holed and ragged young leaves, eaten flower and leaf buds, and deformed fruit covered with corky scars that develop from the damaged fruitlets; under heavy pressure the caterpillars can almost strip the crown bare.