Scots pine

On the needles, especially the older and previous-year ones, yellow and then brown discolourations appear in autumn or late summer, often with dark transverse lines separating the healthy and infected sections. In spring the infected needles turn brown en masse and fall, stripping the lower parts of the shoots. On the dead, fallen needles black, lens-shaped fruiting bodies form, which release spores that infect the new growth; most dangerous to young pines and nursery seedlings. The discolouration usually begins as small yellow spots that spread along the whole length of the needle until it turns reddish-brown. The dark transverse lines (the so-called boundary lines) are the most recognisable feature - they outline the dead sections on a still-green needle. The heaviest needle drop occurs in spring, in April and May, just before the new growth develops; under heavy pressure only the youngest needles at the tip remain on the shoot, giving the characteristic 'paintbrush' habit and weakening growth, while the youngest seedlings may die. The black fruiting bodies on the fallen needles are elongated and boat-shaped, and open with a longitudinal slit in wet weather, ejecting ascospores that infect the freshly grown needles in summer and autumn. Scots pine is the most susceptible, but the disease also affects Austrian pine and dwarf mountain pine. It is worth distinguishing the two causal species: Lophodermium seditiosum is an aggressive parasite of living, young needles and is responsible for damaging needle casts in nurseries, whereas L. pinastri colonises mainly ageing or weakened needles and tends to be a saprotroph - its mere presence on fallen needles need not indicate serious disease.

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.