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This chapter describes and illustrates the damage types (including the possible damaging agents) to foliage of coniferous woody plants: needle nibbling (insects), needle gnawing (insects), rough needle eating (insects), needle curling (insects), needle galling (inscts), needle mining (insects), needle coverings (insects), froth and spittle (insects), needle cast (fungi), rust diseases (fungi), needle blight (fungi), needle webbing (mites), needle clustering (insects, fungi), nesting (insects), and abiotic factors (drought, frost, winter drying, nutrient deficiency, fluctuations in soil pH, air pollution, fungicides, herbicides).

In the past 25 to 30 years, a marked increase has occurred in numbers of invasive alien pests and pathogens recorded, damaging agriculture, horticulture and forest environments. The reasons for this upsurge are clear: all involve human-driven factors, with, arguably, global trade as the most important component in the complex. Climate change is another major factor. Each plant transported through trade could carry cryptic pests or pathogens, which may be introduced into previously naïve environments and lead to major health issues on previously unaffected plants. Global trade in plants is a complex system, driven by a desire to use large plants in landscapes and demand for varied species for gardens. Examples of invasive alien pathogens causing wide-spread problems on a global scale currently include many Phytophthora species, Dothistroma needle blight of pines, and Xylella fastidiosa on a wide range of trees. A striking example recently was the spread of the Dutch elm disease pathogen, Ophiostoma novo-ulmi, in North America and Western Europe. Many invasive pathogens cause problems in localized regions, including Ceratocystis platani, killing Platanus in some European countries. Other examples include the threat of pine wilt nematode (Bursaphelenchus xylophilus), damage to Cupressus in Mediterranean landscapes caused by Seiridium cardinale, dieback of sweet chestnut (Castanea) caused by the canker pathogen Cryphonectria parasitica, and many others. In addition to global trade, climate change appears to be exacerbating the problems, with major influences on establishment and spread of alien invasive species. Hope lies in the enormous genetic ‘power’ of plants: humans could establish selection and breeding programmes that will ultimately enable us to plant trees with greater tolerance of changing climate and pests and pathogens, whether native or invasive.

Heterobasidion is a genus in the Agaricomycetes include some of the most damaging root rot and stem decay-causing agents of conifers in north temperate countries (Asiegbu et al., 2005;Woodward et al., 1998). Economic losses resulting from infections by this species complex were estimated at approximately €800 million annually in European Union forests in 1997 (Woodward et al., 1998), since when losses in the EU are likely to have increased greatly following the accessions of several Central and Eastern European states with large areas of pine forests and plantations. Significant economic losses caused by Heterobasidion species in forestry place members of the genus amongst the most widely studied forest fungi.The H. annosum sensu lato complex, comprising five species in total (Garbelotto & Gonthier, 2013), is represented in Europe by three species: H. annosum (Fr.) Bref. sensu stricto, H. parviporum Niemelä & Korhonen and H. abietinum Niemelä & Korhonen.These species were initially discriminated by apparent host preferences: pine, spruce and fir, respectively, (Niemelä & Korhonen, 1998) and using somatic compatibility tests .Heterobasidion annosum s.s., the subject of this work, was formerly known as the European P group of H. annosum s.l., mostly found attacking and killing pines (Pinus spp.) but also causing decay on a wide range of conifers and broadleaf species (Garbelotto & Gonthier, 2013;Korhonen & Dai, 2005). Two North American species, Heterobasidion irregulare (Underw.) Garbel. & Otrosina and Heterobasidion occidentale Otrosina &Garbel., were fully described more recently (Otrosina & Garbelotto, 2010). Heterobasidion irregulare generally attacks pines, junipers (Juniperus spp.) and incense cedar [Calocedrus decurrens (Torr.) Florin], whereas H. occidentale has a wide host range, including species in the genera Abies, Picea, Tsuga, Pseudotsuga and Sequoiadendro n (Garbelotto & Gonthier, 2013).Primary infections by the fungus occur via basidiospores landing on the surfaces of freshly cut stumps or wounds (Rishbeth, 1950).Once established, the fungus may infect uninjured neighbouring trees by the vegetative growth of the mycelium through root contacts or grafts causing secondary infection of adjacent trees (Garbelotto & Gonthier, 2013). Due to its peculiar biology, entering stands through freshly cut stumps, the fungus is a problem in managed forests, eventually, in the absence of control methods, causing significant reductions in timber production (Asiegbu et al., 2005;

This chapter describes and illustrates the damage types (including the possible damaging agents) to roots and collars of coniferous woody plants: root and butt rot (fungi), root rot (Oomycetes, fungi), bark-feeding insect damage, mammal damage, root and collar-tunnelling (insects), abiotic damage (windthrow, excessive irrigation, excessive heat, planting too deeply, soil compaction, mechanical root damage), root sucking insect damage, root knot (Nematoda, bacteria, insects, fungi), and damage caused by migratory ecto-endoparasitic nematodes.