Sphaeropsis sapinea (Sphaeropsis blight)

A variety of symptoms are exhibited by cones, seed and young seedlings in response to colonization by S. sapinea. Female cones may be killed before full development, becoming dark, shrunken and deformed. Symptoms resulting from in vitro inoculation range from reduced germination to death of seed of several Central American pine species (Rees and Webber, 1988). Radicles of germinants were shortened, thickened and discoloured, and if killed became flaccid and brown. Similarly, Fisher (1941) noted reduced germination and radicle decay for Pinus resinosa and P. ponderosa.Palmer and Nicholls (1985) noted shoot blight of 1-year-old red pine seedlings evidenced by dead terminal buds and upper needles and symptoms on older seedlings including death of new shoots during shoot expansion and needle elongation. Exudation of resin droplets may be the first symptom of infection on either needles or succulent stems. Needles become discoloured and are often killed without elongating beyond fascicle sheaths. Water-soaked, purplish-brown stem lesions may expand as stems become stunted, curled, hardened, resin-encrusted and necrotic (Chou, 1976). Seedlings in nurseries and recently planted seedlings and saplings may be killed by Sphaeropsis collar rot (Palmer and Nicholls, 1985; Stanosz and Cummings Carlson, 1996), characterized by discoloured, necrotic bark and dark discoloration of wood in the lower stem and root collar. Foliage on the entire seedling or sapling becomes chlorotic, desiccated and brown as the stem is girdled.Initial symptoms of shoot blight on established trees resemble those on seedlings, but symptoms become more severe as colonization progresses. The fungus proceeds from killed shoot tips or diseased cones into woody stems to cause cankers (Waterman, 1943; Chou, 1976). Exudation of resin may be copious and dead needles are often retained. On younger stems, smooth bark may be depressed and turn brown as it dies. The underlying wood may be stained green to brown to blue to black and be resin-soaked. Older cankers may be bounded by callus. Entire branches or whorls of branches may be killed as the pathogen progressively invades, and substantial dieback or dead tops can result. Subsequent forking or branching of diseased leaders may result in substantial defect (Currie and Toes, 1978).Severe crown symptoms and tree death may follow hailstorms, drought or pruning. Zwolinski et al. (1990b) estimated loss of as much as half the live foliage, death of 50-80% of leaders, and up to almost 20% tree mortality in Pinus radiata plantations in South Africa in the months after a hail event. Chou (1987) described crown wilt of P. radiata associated with the colonization and killing of inner bark, the extensive invasion and blue staining of wood, and subsequent desiccation. Grey to blue to black staining of wood may occur in freshly cut logs and green lumber (Young, 1937; Kreber et al., 2001) and also in roots colonized by S. sapinea (Wingfield and Knox-Davies, 1980).

Whether or not losses have been expressed in economic terms, significant damage has been caused by S. sapinea in a variety of situations. Palmer and Nicholls (1985) reported loss of 35% of 1-year-old red pine seedlings in a Wisconsin nursery (loss of more than 1 million seedlings). In the same state, mortality of newly planted or established red pine saplings during a drought year was as great as 95% in some plantations. Lower stems and root collars frequently yielded S. sapinea, which proliferates to rapidly girdle and kill many trees under these conditions (Stanosz and Cummings Carlson, 1996; Stanosz et al., 2001). Nicholls and Ostry (1990) reported tree mortality in Pinus banksiana and P. resinosa plantations ranging from 2 to 51% in Minnesota and Wisconsin, and indicated that S. sapinea was consistently associated with dead trees. Trees in windbreaks also have been severely damaged in central USA (Peterson and Wysong, 1968).Losses in the production of Pinus radiata in the southern hemisphere have been reported in more detail. Zwolinski et al. (1990a) quantified the losses resulting from a post-hail outbreak of dieback induced by S. sapinea affecting approximately 2000 ha of mostly P. radiata in the Cape Province of South Africa. The timber loss in compartments prematurely harvested was about 28% of the volume and 55% of the value of potential production. The percentage volume loss increased with plantation age, with the greatest losses recorded on good quality sites. Great losses were also documented for a P. radiata stand affected by S. sapinea in New Zealand (Currie and Toes, 1978). There was a close association between the severity of dieback, tree malformation, and loss in merchantable tree volume. A reduction of 63% in merchantable tree volume was estimated. In contrast, despite a high incidence of top death in some (usually younger) stands of P. radiata in north-eastern Victoria, Australia, the overall effect on tree growth and on volume and value of merchantable wood was small (Wright and Marks, 1970). The volume of degraded wood in this study ranged from 0.5 to 5.5% of the possible volume.