Farm Forestry New Zealand
PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Mycosphaerella leaf spot of Eucalyptus
5 & 6. Mycosphaerella leaf spot of Eucalyptus,
Forest Pathology in New Zealand No. 1.
Compiled: 1983, minor update 1990, revised 2009
Fungus: Mycosphaerella cryptica (Cooke) Hansford and Mycosphaerella nubilosa (Cooke)
Hansford
Type of injury
Leaves become disfigured and drop prematurely. Dieback, stunting, mulileadering and the development of a bushy
habit occurs when infestations are heavy.
Fig. 5 - Dieback of Eucalyptus delegatensis caused by Mycosphaerella cryptica.
Fig. 6 - Upper leaf with Mycosphaerella nubilosa on Eucalyptus globulus, and lower leaf with
M. cryptica on E. delegatensis .
Fig. 7 - Cankers caused by Mycosphaerella cryptica on Eucalyptus delegatensis twigs.
Diagnostic features
Mycosphaerella cryptica: Reddish-brown, irregular-shaped spots with a prominent purple margin present on both sides of young, expanding leaves. Spots eventually turn dark grey. Fruiting bodies develop on both sides of leaves. Infected leaves often distorted and cast prematurely. Cankers (up to 25 mm long) on infected shoots. Gum exudation is often associated with canker development and dieback occurs if cankers girdle shoots.
Mycosphaerella nubilosa: Creamy yellow to pale brown, irregular-shaped spots found on both sides of young, expanding leaves. Spots later turn grey-black on the underside. Fruiting bodies develop on the underside of leaves only.
Hosts
Mycosphaerella cryptica: Eucalyptus dalrympleana, E. delegatensis, E. dendromorpha, E. diversicolor, E. fastigata, E. fraxinoides, E. globulus subsp. globulus, E. globulus subsp. maidenii, E. gunnii, E. macarthuri, E. nitens, E. obliqua, E. ovata, and E. regnans.
Mycosphaerella nubilosa: Eucalyptus botryoides, E. cypellocarpa, E. globulus subsp. bicostata, E. globulus subsp. globulus, E. globulus subsp. maidenii, E. gunnii, E. johnstonii, E. nitens, E. viminalis subsp. viminalis.
Distribution
Throughout New Zealand except for Otago and Southland.
Disease development
Leaf spots appear about 3 weeks after the establishment of infection. The fruiting bodies of theasexual state occur from December to March and spores are splashed-dispersed. Fruiting bodies of the sexual state are present throughout the year and spores are wind-dispersed. Warm (18o to 24oC), moist conditions favour the establishment of infection.
Economic importance
Attack by Mycosphaerella spp can have a marked effect on the growth and form of young trees of the more susceptible host species particularly in damp places such as gullies. Dieback of shoots, if it occurs repeatedly, can result in a stunted, bushy, and multi-leadered tree. Eucalyptus delegatensis and E. regnans are particularly susceptible to M. cryptica. Although E. globulus subsp. globulus is reported to be very susceptible to M. nubilosa in parts of Australia the fungus has not caused any significant damage in New Zealand.
Control
Different provenances of E. delegatensis and E. regnans show a marked variation in their susceptibility to infection by Mycosphaerella; generally, the Tasmanian provenances of both species are the most resistant. Moist sites favour infection and susceptible species should not be planted on such sites. Chemical control is occasionally desirable in the nursery and can be achieved with fortnightly applications of chlorothalonil e.g. 2l Bravo Weatherstik (500g/l of chlorothalonil), and 0.33 litres of wetting agent in 1000 litres of water per hectare.
Bibliography
Dick, M. 1982: Leaf-inhabiting fungi of eucalypts in New Zealand. New Zealand Journal of Forestry Science 12 : 525-537.
Dick, M. 1990: Leaf-inhabiting fungi of eucalypts in New Zealand. II. New Zealand Journal of Forestry Science 20 : 65-74.
Gadgil, P.D. 2005: Fungi on trees and shrubs in New Zealand. Fungi of New Zealand Volume 4. Fungal Diversity Research Series 16: 1-437.
Ridley, G.S., Dick, M. 2001: An introduction to the diseases of forest and amenity trees In New Zealand. Forest Research Bulletin 220, Rotorua, New Zealand.
Dick, M.; Gadgil, P.D. 1983: Eucalyptus leaf spots. New Zealand Forest Service, Forest Pathology in New Zealand No.1.
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