Type: Powdery Mildews; Description: Mycelium superficial, evanescent, occasionally dense, white, hyphae 3–5 μm wide; on leaves. Appressoria not lobed. Ascomata not known in New Zealand. Conidiophores 250–350 × 7–13 μm, foot cell straight or tapering towards the base. Conidia produced in moderately long or long chains, oval, 0-septate, 26–33 × 16–22 μm, smooth, hyaline.

Distribution: Northland, Auckland, Coromandel, Bay of Plenty, Taupo, Wellington, Nelson, Mid Canterbury, Otago Lakes, Southland.; 1st Record: Cunningham (1922: as Sphaerotheca humuli).

Significance: This fungus has been recorded under a number of different names. Dingley (1969) reported it under the name Sphaerotheca macularis (Fries) Jaczewski as the cause of a troublesome powdery mildew on strawberry. Boesewinkel (1980, 1981a) recorded it on a number of Eucalyptus species as S. alchemillae (Greville) Junell. It is the most common of three powdery mildew fungi found on Eucalyptus spp. (The other two are Erysiphe orontii and S. pannosa.) As it is not possible to differentiate these fungi in the field, records generally refer to ‘powdery mildew’ rather than to individual species. Powdery mildew can be a serious problem in glasshouse-grown Eucalyptus seedlings, severe infection causing necrosis of young leaves and shoots. Sphaerotheca aphanis observed in nursery seedlings has been found to persist under field conditions (I.A.Hood, New Zealand Forest Research Institute, pers. comm.).; Host(s): Eucalyptus albens, E. cinerea, E. crebra, E. diversicolor, E. diversifolia, E. grossa, E. megacarpa, E. nitens, E. nutans, E. paniculata, E. tereticornis, E. torquata, Rubus australis, R. cissoides.