Peacock Spot

PEACOCK SPOT Len Tesoriero This is No. 8 in a series of 9 tutorials on IPDM in olives The others are: 1. Principles and practices of Integrated Pest and Disease Management 2. Monitoring for pests, diseases and beneficial species, including symptoms and possible causes, identification/diagnostic services 3. Biosecurity, including pests and diseases not present in Australia 4. Black scale: biology, damage and management 5. Olive lace bug: biology, damage and management 6. Apple Weevil: biology, damage and management 7. Anthracnose: life cycle, conditions conducive, symptomatology and damage, and management 9. Cercospora leaf mould: life cycle, conditions conducive, symptomatology and damage, and management It is an output from the Hort Innovation project OL17001 An Integrated Pest and Disease Management Extension program for the Olive Industry PEACOCK SPOT Fusicladium oleaginum (Spilocaea oleaginea) • A fungal disease also known as Olive Leaf Spot • Occurs worldwide and is the most common disease of olives • ‘Peacock spot’ refers to the typical circular leaf spots that resemble the dark markings of male peacock tail feathers • This disease is common in regions that experience wet and humid spring conditions – particularly coastal and warm temperate regions of Australia PEACOCK SPOT - initial leaf symptoms • Initial symptoms can be difficult to distinguish – whitish/pale grey circular spots on the upper leaf surface PEACOCK SPOT – typical leaf symptoms • Spots can develop a dark outline, concentric markings or a yellow halo • Infected leaves yellow before dropping PEACOCK SPOT – fruit symptoms • Under moist weather conditions developing fruit can also be infected – although this isn’t common 2-celled spores of Fusicladium BIOLOGY & LIFE CYCLE • Infection of leaves occurs mostly in winter & spring during wet weather (optimum temperatures 15-21oC, >98% Relative Humidity and a wet leaf surface for 1-2 days). Spores cannot germinate >25oC and infection takes 60 hours at 25oC. • Infections can remain dormant until autumn if conditions are dry – called a ‘latent infection’ • After periods wet weather lesions develop and conidia (spores) form on the leaf surface • Spores spread with water splash & with insects such as booklice (Order Psocoptera) which live in leaf litter & on leaves • Olive varieties differ in susceptibility – e.g. Hojiblanca, Picual, Arbequina & Manzanillo are more susceptible; Lecchino is more resistant LIFE CYCLE Fusicladium oleaginum Infection of leaf – under cuticle Latent Infection in dry weather Peacock Spot Fungus Life Cycle Rain splash & insects disperse spores Wet & humid weather Fungus emerges from leaf surface & Spores (conidia) develop leaf symptoms develop MANAGEMENT OPTIONS • Remove or cover dropped leaves with compost - or shred leaves and apply N fertiliser to hasten breakdown in winter • Prune branches to open up canopy to air/sun • Apply fungicides – timing is important (especially in late winter & spring) • Grow tolerant olive varieties • Maintain balanced plant nutrition in spring – high nitrogen and low potassium levels in leaves favour infection REVIEW QUESTIONS • Q1: Why does Peacock Spot most commonly occur only in coastal and warm temperate areas? • Q2: Outline preventative strategies for reducing the risk of this disease. ANSWERS • Q1: This disease requires extended periods of mild wet weather for spore germination, successful infection and a build-up of inoculum (for instance you need 1-2 days of wet leaves for successful infection); & extreme hot and dry weather kills fungal spores. • Q2: Grow tolerant or resistant varieties; remove or cover fallen leaves in winter; prune to open up the tree canopy; apply preventative fungicides when wet weather is expected – particularly in late winter and early spring; and avoid excess nitrogen fertiliser applications QUESTIONS TO CONSIDER AFTER READING THIS TUTORIAL • Do you have peacock spot in your grove and how severe is it, from year to year? • What are your strategies to minimise it? • How effective have your strategies been, and are there additional or alternative strategies you could employ? FURTHER READING • Nigro E, Antelmi I & Sion V (2018) Integrated control of aerial fungal diseases of olive. Acta Horticulturae. 1199.51 ISHS. Eds: S. Perica et al. 327-332 • Trapero A & Blanco M (2010) Diseases - Chapter 15 in Olive Growing Eds D Barranco, R Fernandez-Escobar & L Rallo RIRDC Australia, 525-535. • González-Dominguez E, Armengol J & Rossi J (2017) Biology and epidemiology of Venturia species affecting fruit crops: A Review. Frontiers in Plant Science, 8 Article 1496. This project has been funded by Hort Innovation using the olive research and development levy, co-investment from the Australian Olive Association and Western Sydney University and funds from the Australian Government. For more information on the fund and strategic levy investment visit horticulture.com.au .

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