Leaf spot diseases

Target spot (Aulographina eucalypti)

• Target spot is one of the most common and distinctive leaf diseases of eucalypts in south-eastern Australia.
• Roughly circular leaf spots are 1–15mm in diameter and mostly single.
• Spots are yellow-brown to dark brown with a concentric pattern, hence the name 'target spot'.
• They often occur along the midrib and will coalesce when there are many.
• They are also common on petioles (leaf stalks).
• During cooler weather, a purple margin can develop around the lesions.
• Spots are often raised and corky.
• They occur on upper and lower leaf surfaces, but rarely penetrate through to the opposite side of the leaf.
• Distinctive black fruiting bodies (sporocarps) are often seen within spots, and are only formed on 1 leaf surface.
• Young leaves, including coppice shoots, are more susceptible than older, hardened leaves.
• Lesions are larger and more visible on older leaves lower in the canopy.

Corky leaf spot (Microsphaeropsis species)

• Spots are small, up to 2mm in diameter.
• They are yellow-brown to dark brown and corky in appearance.
• They are scattered across the whole leaf, and often coalesce to form larger spots, usually on the leaf margins.
• Spots occur mainly on the lower surface of leaves, but are also found on the upper surface.
• They are mostly found on older leaves in the lower crown, or coppice shoots.

Marksii leaf spot (Mycosphaerella marksii)

• Circular to irregular expanding spots are 3–20mm in diameter.
• Spots are yellow to red-brown on the upper leaf surface and grey on the lower surface. They vary on different hosts:
  • On Eucalyptus pilularis, spots are red-brown, circular to irregular (12mm in diameter), often with an irregular, raised margin, and often coalescing.
  • On E.grandis, E. saligna and E. dunnii, leaf spots are yellow-brown with a raised red-brown border, mostly circular (12mm in diameter), and coalescing when there are many.
• Sometimes spots are more common towards leaf margin, where they coalesce to form larger spots.
• Fruiting bodies are seen mostly on the upper leaf surface.
• Spots affect mainly older, lower foliage, causing defoliation of the lower canopy.

Purple leaf spot (Phaeothyriolum micothyrioides)

• Circular spots are usually 5–50mm in diameter but can be larger.
• Each spot starts as a chlorotic yellow spot and becomes purple, then brown and grey with age.
• There is variation in spot appearance depending on the host.
• Spots occur on both leaf surfaces but rarely extend through to the opposite side of the leaf.
• Black fruiting bodies form within spots, often before the spots turns purple.
• Concentric rings of fruiting bodies and/or discolouration may be seen on otherwise healthy leaves.

Coniella leaf blight (Pilidiella eucalyptorum)

• Large circular or irregular yellow-brown, red-brown or greyish black spots begin on leaf margins and spread to form large blights.
• There can be many spots per leaf and they often cover most of or the entire leaf.
• Lesions can also occur on petioles and twigs.
• The leaf often curls as it dries and is shed.
• Small black fruiting bodies are seen in concentric rings within spots and blights, mostly on the upper leaf surface.
• During wet weather an off-white to pale yellow or brown conidial ooze is produced by the fruiting bodies, and is dispersed by rain splash.
• Symptoms usually occur in the lower part of the crown of young trees, or on coppice shoots.
• Infestation often follows a pathogen attack (such as myrtle rust) or insect or physical damage. However, it can also be the primary pathogen in wet weather.

Target spot (Aulographina eucalypti)

• Eucalypts in south-eastern Australia (very common)
• Brisbane and Cairns areas

Corky leaf spot (Microsphaeropsis species)

• Throughout Queensland and Australia, from temperate to tropical areas

Marksii leaf spot (Mycosphaerella marksii)

• Along the eastern coast of Australia from Cairns to Victoria, and in Western Australia

Purple leaf spot (Phaeothyriolum micothyrioides)

• Throughout mainland Australia and Tasmania

Coniella leaf blight (Pilidiella eucalyptorum)

• Throughout Queensland, northern New South Wales and southern Australia

Target spot (Aulographina eucalypti)

Mostly occurs on Eucalyptus species.

• Smooth-barked apple (Angophora costata)
• Gympie messmate (Eucalyptus cloeziana)
• Dunn's white gum (E. dunnii)
• Rose gum and hybrids (E. grandis)
• Shining gum (E. nitens)
• Blackbutt (E. pilularis)
• Sydney blue gum (E. saligna)

Corky leaf spot (Microsphaeropsis species)

Only occurs on Eucalyptus species.

• Rose gum (Eucalyptus grandis)
• Sydney blue gum (E. saligna)

Marksii leaf spot (Mycosphaerella marksii)

• Spotted gum hybrid (Corymbia torelliana × C. citriodora subspecies variegate)
• Dunn's white gum (E. dunnii)
• Southern blue gum (E. globulus)
• Rose gum (E. grandis)
• Large-fruited red mahogany (E. pellita)
• Blackbutt (E. pilularis)
• Sydney blue gum (E. saligna)
• Turpentine (Syncarpia glomulifera)

Purple leaf spot (Phaeothyriolum micothyrioides)

• Spotted gums (Corymbia citriodora subspecies variegata, C. henryi, C. maculata)
• Other Corymbia species
• Eucalyptus species (rarely)

Coniella leaf blight (Pilidiella eucalyptorum)

Has a wide host range, including Eucalyptus species.

• Dunn's white gum (Eucalyptus dunnii)
• Southern blue gum (E. globulus), in India
• Rose gum (E. grandis)
• Large-fruited red mahogany (E. pellita)
• Sydney blue gum (E. saligna), in Brazil

Target spot (Aulographina eucalypti)

• Damage occurs mostly on older, lower foliage.
• Severe leaf infection and damage to petioles and small branches leads to premature defoliation.
• Defoliation mainly occurs in the lower crown.

Corky leaf spot (Microsphaeropsis species)

• Heavily infected leaves often turn purple on the upper surface.
• There is premature fall of mature leaves in the lower, inner canopy.

Marksii leaf spot (Mycosphaerella marksii)

• Spots affect mainly the older, lower foliage, causing defoliation of the lower canopy.
• This species has impacted eucalypt plantations overseas, but is not of major concern in Queensland.

Purple leaf spot (Phaeothyriolum micothyrioides)

• Spots affect mature and old leaves.
• They rarely cause defoliation.

Coniella leaf blight (Pilidiella eucalyptorum)

• Spots often affect older foliage in the lower crown, or coppice shoots.
• Photosynthetic rates are reduced.
• Heavily infected leaves are prematurely shed.
• Lesions can also occur on petioles and twigs.
• This disease is usually a minor concern to plantation growers, but has led to significant foliage damage and defoliation following higher than average rainfall.
• It often follows a pathogen attack (such as myrtle rust) or insect or physical damage, but can be the primary pathogen in wet weather.

Target spot (Aulographina eucalypti)

• Elongate or branched fruiting bodies called hysterothecia are scattered on the surface of the 'corky' leaf spots.
• Sporulation occurs when hysterothecia are wet and in temperatures from 15 to 20 degrees Celsius.
• Infection occurs mainly during spring and early summer on susceptible young leaves.
• Lesions on lightly infected attached leaves—and also in leaf litter, on petioles, and on fruits and smooth bark of some eucalypt species—survive for a considerable time and are likely to be important sources of inoculum.

Corky leaf spot (Microsphaeropsis species)

• The fruiting bodies (pycnidia) are easily seen with the naked eye.
• They are embedded in the leaf surface and extrude small dark-brown to black spores.
• Sporulation is generally sparse.

Marksii leaf spot (Mycosphaerella marksii)

• The black fruiting bodies (ascocarps) are usually prominent on the lower leaf surface, rarely on the upper surface.
• They are closely crowded and project through the epidermis.
• Release of ascospores requires high (>85%) humidity and leaf wetness.
• Ascocarps hibernate at temperatures below 5 degrees Celsius.

Purple leaf spot (Phaeothyriolum micothyrioides)

• Minute black fruiting bodies are arranged in a circular or semicircular pattern on both leaf surfaces.
• Optimal ascospore discharge occurs between 5 and 10 degrees Celsius.
• Symptom development is greatest during cooler months.

Coniella leaf blight (Pilidiella eucalyptorum)

• The small black fruiting bodies are usually arranged in concentric rings within leaf spots and mostly occur on the upper leaf surface.
• Fungal spores are spread by rain splash.
• Disease development increases during humid conditions.

• Most attacks of leaf spot diseases are sporadic and not usually of concern.
• Established trees typically recover.
• The growth rates of young trees may be reduced and seedlings may be killed.
• No control measures are needed, but any unusually susceptible plants should be eliminated from provenance or clonal trials.

• Carnegie, AJ, Lawson, SA, Smith, TE, Pegg, GS, Stone, C, McDonald, JM, 2008, Healthy hardwoods: a field guide to pests, diseases and nutritional disorders in subtropical hardwoods, Forest & Wood Products Australia, Victoria.
• Carnegie, AJ, Pegg, GS, White, D, Burgess, TI, 2011, Species within Mycosphaerellaceae and Teratosphaeriaceae from eucalypts in eastern Australia, Australasian Plant Pathology, 40:366–384.
• Old, KM, Wingfield, MJ, Qing Yuan, Z, 2003, A manual of diseases of eucalypts in South-East Asia, Center for International Forestry Research, Canberra.
• Park, RF, Keane, PJ, Wingfield, MJ, Crous, PW, 2000, Fungal diseases of eucalypt foliage. In PJ Keane, GA Kile, FD Podger, BN Brown (Eds.) Diseases and Pathogens of Eucalypts, pp. 153–239, CSIRO Publishing: Melbourne.
• Van Niekerk, JM, Verkley, GJ, Fourie, PH, Wingfield, MJ, Crous, PW, 2004, Systematic reappraisal of Coniella and Pilidiella, with specific reference to species occurring on Eucalyptus and Vitis in South Africa, Mycological Research, 108(3):283–303.