Outbreaks of dieback and stem cankers formed by Diplodia pinea occur sporadically throughout New Zealand. Unthrifty trees and trees suffering mechanical injury are attacked. The disease sometimes causes substantial losses in forests of exotic conifers. Curtis (1926) recorded the fungus causing severe dieback on Pinus radiata and P. muricata following drought injury. Birch (1936) associated the disease with a red top symptom in P. ponderosa, P. contorta, P. nigra, and P. radiata among unthinned and overstocked stands on pumiceous soils. Grayburn (1957) recorded a severe attack of Diplodia in north Canterbury on Pinus radiata, P. nigra, and P. ponderosa following hail injury. Gilmour (1964) (1965b) recorded the occurrence of this fungus as a wound pathogen following thinning and low pruning in three- to 10-year-old P. radiata trees growing in pumice soils in the central North Island.

Type: Caulicolous Fungi; Description: Conidiomata pycnidial, scattered or in groups, immersed, partly erumpent (particularly on needles), dark brown to black, 0.3–0.5 mm in diameter, ostiolate; on wounds on stems and on unwounded, non-suberised shoots and needles. Conidia oblong to clavate, 0-septate (sometimes becoming 1-septate on germination), 30–55 × 11–18 μm, smooth or pitted, dark brown.

Distribution: Northland, Auckland, Coromandel, Waikato, Bay of Plenty, Taranaki, Taupo, Rangitikei, Wanganui, Wellington, Gisborne, Hawkes Bay, Wairarapa, Nelson, Buller, Westland, Marlborough, Kaikoura, North Canterbury, Mid Canterbury, South Canterbury, Mackenzie, Otago Lakes, Central Otago, Dunedin, Southland.; 1st Record: Curtis (1926: as Botryodiplodia pinea).

Significance: This ubiquitous fungus, generally considered to be a wound pathogen, is also capable of infecting undamaged young tissue. It attacks tissues weakened or damaged by frost, drought, hail, or mechanical injury, and causes two main types of damage: Leader dieback: Infection of tissue produced in the current season results in dieback of terminal and lateral shoots. The first sign is a small, dark brown spot on the non-suberised young shoot; this develops into a purple to dark brown lesion which does not extend to the suberised part of the stem. The shoot wilts at the point of infection and the part above the lesion dies. Warm temperatures (20–25pC) and humid conditions favour infection (Chou 1982). Leader dieback is a problem in a few localised areas, principally closed valley systems. Malformation associated with leader dieback can cause significant downgrading of sawlog quality. It was responsible for an estimated loss of $5.4 million (1988 dollars) over one rotation in a 6000 ha plantation (New 1989). Crown wilt and whorl canker: Infection of the woody stem can lead to death of a considerable portion of the crown, the extent depending on position of the point of entry. The fungus invades through wounds and pruning stubs are common entry sites. Depressions form above and below infected stubs because the cambium is killed, causing a type of injury known as whorl canker. If all pruning stubs in a branch whorl are affected, the whole portion of the crown above the whorl often dies. Infection of woody tissues is first indicated by discoloration and death of the inner bark, which becomes brown and eventually black. The fungus reaches the pith through the ray cells and invades further ray cells as it moves up the stem. Infected wood ranges in colour from light grey to dark blue grey. This ‘blue stain’ is usually seen in cross section as wedge-shaped sectors. Wilting of shoots or the whole crown follows invasion of the wood. Chou & MacKenzie (1988) showed that the extent of pruning affected susceptibility of Pinus radiata trees to S. sapinea. Where 40–50% of the green crown was removed in a single lift, 65% of the trees became infected; only 8% were infected where pruning involved 25% crown removal. Chou & MacKenzie (1988) also showed that infection was restricted to a short period during summer months. Chou (1987) found that water stress caused by drought was a predisposing factor. Damage from whorl canker and crown wilt can therefore be minimised if 25% or less of the green crown is removed in one pruning lift timed to avoid hot and dry periods in summer. Sphaeropsis sapinea is also important as a cause of sap-stain in logs and sawn timber.; Host(s): Chamaecyparis lawsoniana, Pinus canariensis, P. contorta, P. elliottii, P. muricata, P. nigra subsp. laricio, P. palustris, P. ponderosa, P. radiata, P. taeda, Pseudotsuga menziesii.