Rust'n'Honey Fungus

Jonathan Garner continues his look at recognising and managing pathogens.

- Jonathan Garner

I hope our chat last issue helped explain what Phytophthora is and what can be done to reduce the risks. I hope after this chat you'll be armed with a better understanding of two other nasties that, if left unmanaged, can cause significant damage to your landscape asset and the surrounding environment.

Armillaria

Armillaria - better known as Honey Fungus - gets its name from the honey-coloured mushrooms it produces in autumn and into winter. Armillaria is a destructive disease that can slowly kill trees and shrubs, is notoriously difficult to manage, and can persist in the soil for decades.

Similar to Phytophthora, its ecological role is to remove sick or weakened plants from the environment. However, unlike Phytophthora, which simply kills its hosts, Armillaria is a necrotrophic pathogen - meaning it kills its host and then rapidly consumes or decomposes it.

There are over 250 species of Armillaria worldwide, and several are native to Australia. Interestingly, a species found in Oregon, USA, is believed to be the world's largest single living organism. Nicknamed the 'Humongous Fungus,' it spans an estimated 910 hectares and weighs around 35,000 tonnes, with an estimated age of 8000 years.

Who needs a disease like this?

Before we dig deeper into this nasty pathogen, consider why a fungus that targets sick or weakened plants is such a big problem in managed landscapes. Many landscape plants, especially those planted outside their optimal growing conditions, can be considered 'weakened' and therefore highly susceptible. It's safe to assume all woody trees and shrubs are at risk of Honey Fungus given the right conditions.

What to look for