Cunningham (1925a) recorded mildew on peach trees and described a distinct blotch on fruit of some varieties, especially `Stark', 'Paragon', and `Golden Queen', in the Hastings area. Hawke's Bay. A similar fruit blotch referred to as `mapping' has been recorded from Central Otago on apricots (Anon., 1963b). On roses it is common throughout New Zealand during the summer months (Marcussen, 1962). It may be controlled with regular sprays with a mixture of lime sulphur and colloidal-sulphur, or with dinocap. It is of importance both in stone-fruit and commercial rose nurseries.

Type: Powdery Mildews; Description: Mycelium superficial, moderately dense to dense; on leaves, shoots, and inflorescences. Primary mycelium white, composed of flexuous hyphae; secondary mycelium brown, composed of straight hyphae; hyphae of both types 5–6 μm wide. Appressoria not lobed. Ascomata cleistothecial, scattered, superficial on the plant surface but embedded in ‘pannose’ or felted patches of the secondary mycelium, globose to pyriform, dark brown, 0.1 mm in diameter, with a few short, unbranched, twisted, pale brown appendages. Asci one per ascoma, oblong to globose, 80–115 × 60–75 μm. Ascospores 8 per ascus, oval, 0-septate, 20–27 × 12–15 μm, smooth, hyaline. Conidiophores 70–80 × 7–9 μm, foot cell slightly swollen at the base. Conidia produced in long chains, oval, 0-septate, 27–31 × 15–18 μm, smooth, hyaline.

Distribution: Northland, Auckland, Coromandel, Waikato, Bay of Plenty, Taranaki, Taupo, Wanganui, Wellington, Hawkes Bay, Nelson, Mid Canterbury, South Canterbury, Central Otago, Otago Lakes, Dunedin, Southland, Chatham Islands.; 1st Record: Kirk (1905).

Significance: The cause of ‘rose mildew’, a damaging disease of cultivated roses. When infection is severe, entire leaves, long stretches of stem, buds, and flowers become covered with white, powdery mycelium; leaves wither and growth is checked. Leaf infection in peach and apricot is uncommon but russeting of fruit is troublesome in susceptible varieties (Atkinson 1971). Boesewinkel (1981a) has shown that this species occurs on species of Eucalyptus. Because it is difficult to distinguish from other powdery mildews in the field, its significance as a pathogen of eucalypts is discussed under Sphaerotheca aphanis.; Host(s): ): Eucalyptus albens, E. deglupta, E. eremophila, E. moluccana, E. tereticornis, Malus × domestica, Prunus armeniaca, P. persica, Rosa chinensis × multiflora, *R. multiflora, *R. rubiginosa, * Rosa sp.