Mountain 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.

Immobile, brown or yellowish shields (1-4 mm) attached to stems and the underside of leaves, especially along the veins. Easily mistaken for growths on the plant. They suck sap, causing yellowing and weakening, and excrete sticky honeydew. Common on figs, orchids and plants with tough leaves. The collective name covers two groups with different biology. Armoured scales (Diaspididae) have a hard waxy shield separate from the body, which can be prised off - beneath it emerges a tiny, legless and wingless female; they do not excrete honeydew. Soft scales (Coccidae) have a convex, cup-shaped cover fused with the body, and it is they that excrete it abundantly. Sticky honeydew - the domain of soft scales and other honeydew-producing scale insects, not of armoured scales - settles on the leaves and attracts sooty mould fungi (sooty mould, sooty blotch) as well as ants, which defend the colony against predators. The only mobile feeding stage is the crawler - a flat, tiny larva which, after hatching from beneath the mother's shield, disperses over the plant, then settles, inserts its stylet into the conducting tissues and loses the ability to move; adult females remain immobile for the rest of their lives. Males pupate and, as tiny, winged, short-lived insects, do not feed. In heated interiors the pest breeds all year round, producing several overlapping generations; outdoors usually 1-3 generations, and fertilised females or eggs hidden beneath the shield overwinter. Feeding symptoms are yellowing and premature leaf drop, dieback of shoots, stunting and weakening of the plant, and secondarily a black coating of sooty mould on leaves covered with honeydew. On fruit trees infested by San Jose scale (Comstockaspis perniciosa), reddish discolouration appears around the feeding sites, and heavily colonised branches die back. Because the shields are immobile and their colour blends into the bark and veins, an infestation is easily overlooked until honeydew appears or the plant is noticeably weakened - which is why regular inspection of the leaf undersides and shoot axils is key.