eucalyptus leaf blotch

Symptoms

Large irregular brown-purple blotches on juvenile leaves, premature leaf drop reducing biomass growth, mature crown foliage usually resistant.

Plants affected

• river red gum
• Tasmanian blue gum

Easily confused with

• drought stress

  How to tell them apart: Drought stress on Eucalyptus camaldulensis shows diffuse browning that follows the leaf margins and tip, with a yellow-to-tan chlorotic transition into healthy green and no discrete spots, dark borders, or fruiting structures; it appears worst on the sun- and wind-exposed side and across the whole canopy at once, with crispy, brittle foliage. Mycosphaerella nubilosa (Teratosphaeria nubilosa) instead produces discrete, rounded-to-irregular lesions 5-25 mm across that start pale green with purple margins and mature to yellow or pale brown with raised dark-brown borders, often coalescing into larger blotches; turn the leaf over and you can see tiny grey-black fruiting bodies (perithecia) on the lower surface. The clincher is that drought has no defined lesion edges or fungal fruiting bodies and tracks the leaf margin, whereas the fungus makes bordered, blotchy spots concentrated on younger juvenile foliage.

Common questions

How do I recognise eucalyptus leaf blotch on river red gum?

Large irregular brown-purple blotches on juvenile leaves, premature leaf drop reducing biomass growth, mature crown foliage usually resistant.

Do I have to report eucalyptus leaf blotch?

No. eucalyptus leaf blotch is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is eucalyptus leaf blotch treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.