Gilmour (1961) in a random survey of fungi associated with needle cast of Pinus spp. in New Zealand showed that Naemacyclus was common. Gilmour (1966a) stated that it was particularly severe after the cool, wet summers in 1953, 1956, and 1962. It is of minor economic importance.

Type: Foliicolous Fungi; Description: Ascomata apothecial, scattered, subepidermal, somewhat rectangular in appearance when partially open, elliptical when fully open, waxy, reddish-brown when young, later becoming concolorous with the needle surface, 0.1–0.65 (mostly 0.3–0.35) × 0.2–0.25 mm; as they develop, emerging through the needle epidermis, which is torn but remains hinged; swelling when mature and moist, pushing back the hinged epidermis to expose a slightly convex, straw-coloured hymenial layer; rarely found on needles before they are shed but developing rapidly on fallen needles. Asci subcylindrical, 90–110 × 8–10 μm. Ascospores filiform, 0–2-septate, 65–85 × 2–3 μm, hyaline. Conidiomata pycnidial, scattered, immersed, globose to subglobose, 0.1–0.2 mm in diameter. Conidia bacilliform, 0-septate, 6–10 × 1 μm, hyaline.

Distribution: (* = districts with a high incidence) *Northland, *Auckland, Coromandel, *Waikato, *Bay of Plenty, Taranaki, *Taupo, Rangitikei, Wanganui, Wellington, *Gisborne, Hawkes Bay, Wairarapa, Nelson, Buller, *Westland, Fiordland, Marlborough Sounds, Marlborough, North Canterbury, Mid Canterbury, South Canterbury, Otago Lakes, Central Otago, *Dunedin, *Southland.; 1st Record: Gilmour (1959: as Naemacyclus niveus).

Significance: Cyclaneusma minus has been experimentally shown to be able to infect Pinus radiata plants older than 3 years of age over temperatures ranging from 10º to 25ºC (Gadgil 1984). In susceptible trees, infection by the fungus leads to disease, which is characterised by premature casting of 1-year-old or older needles, mainly in spring but also, to a lesser degree, in autumn. Cast needles are usually a mottled yellow brown in colour. Ascomata of C. minus are rarely seen on needles still attached to the tree but are very common on fallen needles. Ascomata production occurs throughout the year but the greatest number of ascomata per unit area is produced during autumn and winter (May–August). Ascospores are forcibly ejected from the ascomata after about 2 hours of rainfall and are wind-dispersed. Airborne ascospores can be trapped throughout the year but are most numerous during autumn and winter months. Current season’s needles are resistant to infection by ascospores until they are 8–9 months old. They become infected in autumn–early winter (May–June), begin to develop yellow brown mottling by July and are usually cast in early spring, when about one year old. At least two morphologically distinct types of C. minus have been found in the New Zealand population but whether these morph-ological differences reflect differences in pathogenicity is unknown (Dick et al. 2001). Aerial surveys of forests throughout New Zealand have shown that the severity of needle-cast was highest in 11–20-year-old stands and lowest in 1–5-year-old and over 25-year-old stands (Bulman 1988). In all districts, microsites, particularly those at high altitudes, had a high incidence of the disease. Trees vary in susceptibility and even in districts where conditions are favourable to infection less than 60% of the trees in a stand usually show symptoms. Trials carried out to explore the relationship between disease severity (expressed as a percentage of the green crown showing symptoms of the disease) and growth have shown that an average disease severity of 60% over six years resulted in a 50% loss in diameter increment (Bulman & van der Pas 2001). Projections of stand growth to age 30 for various proportions of diseased trees predicted a reduction in volume 10–14 m3/ha for each 10% increase in the proportion of diseased trees. For the country as a whole, growth loss of 6.6% per annum for the P. radiata estate aged between 6 and 20 years was predicted. The corresponding financial loss was estimated to be of the order of $51 million per year (Bulman 2001a). Fungicide screening trials have shown that fortnightly applications of dodine or injection with carbendazim were able to control the disease. Two aerial applications of carbendazim a month apart gave no control but monthly aerial applications of dodine for 6 months gave good control. The cost of such measures is not economically justifiable (Hood & Bulman 2001). Silvicultural trials have indicated that stocking density and pruning have no effect on disease incidence or severity. Trials carried out to test the effect of applying different thinning ratios at different crop ages showed that, using susceptibility to the needle-cast as a main criterion for tree selection, a delayed first thinning at age 7 or 8, followed by a second thinning at age 10 succeeded in achieving an almost disease-free final crop stand (Bulman 2001b). Cyclaneusma needle-cast is a disease of complex aetiology and the interactions between host genotype, host nutrition and the variable fungal population are not fully understood. Much work on these aspects remains to be done.; Host(s): Pinus attenuata, P. ×attenuradiata, P. brutia, P. contorta, P. densiflora, P. jeffreyi, P. monticola, P. mugo subsp. mugo, P. mugo subsp. uncinata, P. muricata, P. patula, P. ponderosa, P. radiata, P. strobus, P. sylvestris, P. yunnanensis, Pinus sp.