Dog rose

Black to dark-brown spots with ragged margins on rose leaves, surrounded by yellowing of the leaf blade. Infected leaves drop in large numbers, weakening the plant and reducing flowering. The disease intensifies in wet seasons and where air circulation is poor. The spots are usually round, from a few millimetres to about 1-1.5 cm across, and their most important diagnostic feature is the radially fringed, feathery margin - the mycelium spreads beneath the leaf cuticle in all directions, producing the characteristic 'star-shaped' edge (hence the German name Sternrußtau). Under heavy infection the spots merge into larger, irregular patches, and the surrounding yellowing spreads across more and more of the blade until the whole leaf turns yellow and drops. Small, dark conidial fruiting bodies (acervuli) appear on the upper surface of the spots, while the underside of the leaf remains free of any coating. Symptoms appear first on the lower, oldest leaves and gradually move up the shrub, because the spores are carried by water splashing up from the soil and from lower leaves. Small, purplish-red discolorations and blotches may appear on young, green shoots. Prolonged wetting of the leaves for several hours is required for the spores to germinate and infect, which is why the disease breaks out after warm, rainy spells. Repeated defoliation exhausts the shrub, limits flowering and worsens winter hardiness.

Rusty-orange to brown, powdery clusters of spores on the underside of leaves, matched on the upper side by yellow spots. Heavily infected leaves turn yellow and drop prematurely, and the plant weakens. It affects roses and mallows among others, and some rusts have an alternate host (for example pear rust and juniper). The pustules (clusters of summer spores, the so-called uredinia) break through the leaf skin and release an orange-rust powder that rubs off onto the finger - this is the most reliable identifying feature. In high summer they appear mainly on the underside of the blade, along the veins and on the leaf stalks, and in some species also on green shoots and sepals. In late autumn the clusters darken to brownish-black - these are the overwintering spores (telia) by which the fungus survives winter on plant debris. Rusts are highly host-specific: a given rust usually infects only one species or genus of host, which is why the rusts of rose, mallow and marsh mallow, bean, leek and garlic, mint, pelargonium or lawn are different, non-interchangeable fungi. The general symptom - yellowing and premature leaf drop - weakens the plant and limits flowering and yield, though it rarely kills it within a single season.

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.

The larvae strongly resemble the caterpillars of butterflies and moths, but have more pairs of abdominal prolegs (six and more) and single ocelli on the sides of the head, by which they can be told apart. They often feed gregariously, skeletonising the leaves or eating them down to the veins, and can strip a gooseberry or currant bush bare within a few days. The host plants are gooseberry, currant, rose, plum and pine. Symptoms: besides the defoliation of leaves, the larvae of fruit-dwelling species (e.g. on plum) bore into the young fruit set and cause it to drop. Adult sawflies are small (a few millimetres) hymenopterans without a distinct 'wasp waist' — the abdomen is broadly joined to the thorax, which distinguishes them from wasps and bees; the females have a saw-like ovipositor (hence the name 'sawflies'), with which they cut into the tissue of a leaf or fruit set and lay their eggs inside it. The larvae are most often green, matching the colour of the leaf, in some species with dark warts or spots; their prolegs lack the grasping crochets that the caterpillars of moths have, and when disturbed the larvae of many species raise the rear end of the body into a characteristic 'S' shape. The most damaging groups are: the gooseberry sawfly (Nematus ribesii) on gooseberry and currant, stripping the bush from the inside out; the slug sawflies (genus Caliroa) on pear, cherry and plum, whose slimy, slug-like larvae graze away the upper skin of the leaf (windowing), so that the leaf turns brown as if scorched; the fruit sawflies of the genus Hoplocampa on plum and apple, tunnelling galleries into the young fruit set and leaving moist, foul-smelling droppings; and the conifer sawflies (Diprion, Neodiprion) on pine, feeding gregariously on the needles. Life cycle: the adults emerge in spring, the larvae feed for several weeks, after which they descend into the soil or leaf litter, where they pupate in a cocoon and overwinter as a larva (prepupa); depending on the species, 1–3 generations develop in a season.

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.