With blackberry infesting roughly 8.8 million hectares of temperate Australia, biological control remains the only viable management option for many infestations (CSIRO, 2011). In South Gippsland there is a great deal of community interest in leaf rust-fungus as a tool for controlling blackberry. Below are some of the frequent questions I'm asked about the biological control agent.
What is blackberry leaf rust-fungus?
A defoliating disease host specific to European blackberries approved for use in Australia. The rust-fungus has fruiting bodies (spores) that damage leaves occasionally green stems, stalks, sepals and unripened fruit and is capable of causing severe defoliation in susceptible species given the right conditions.
What are the right/suitable conditions for the leaf rust-fungus to establish?
Light is one of the more important requirements, generally sites that have full sun and or very little shade are suitable. Sites in open woodland, open creek lines and fence lines etc are preferable. Shaded sites are typically not suitable. Rainfall and temperature are the other important factors. Sites receiving an annual rainfall of 800mm or greater with an average maximum daily temperature of about 20°C for the month of January are more likely to be successful (Weeds CRC 2005).
Is the blackberry leaf rust-fungus safe?
Rust spores are not toxic to humans and animals but may cause irritation to people sensitive to pollens and dusts. In such cases, it is recommended to wear safety equipment such as goggles, a respiratory mask and gloves when handling rust spores or infected foliage (CSIRO 2011). Strains of the blackberry leaf-rust fungus (Phragmidium violaceum) were thoroughly tested by the CSIRO before approval was obtained to release it in the environment. They were shown in host-specificity tests to be highly specific towards weedy European blackberries.
Sounds like a cheap & easy way to solve my blackberry problem! Where can I get some?
You may already have the leaf-rust on your property it's widely established in Australia including in South Gippsland; spores of the blackberry leaf-rust are spread by wind and can travel long distances in relatively short periods of time. Although it can be effective, the leaf-rust will not completely kill a blackberry plant. The leaf-rust relies upon its host to survive, its not going to eat itself out of house and home now is it? Also keep in mind that Biological control will not be effective across the range where blackberry infestations occur and therefore an integrated weed management approach will be necessary if effective control is what you're after. If effective control is not viable given the size and location of the infestation and costs associated with control etc then the leaf-rust is particularly useful.
What if effective/thorough control is viable for me and my situation?
Then don't rely solely on the leaf-rust fungus, use a combination of control measures, (termed integrated control) at an on-going and landscape scale i.e. talk to your neighbours; have a year by year action plan based on resources at your disposal and, (to quote USA sports brand, Nike) Just Do It! True recovery of large areas of land for the production of pasture and the establishment of seedlings in plantation forests should only be expected following this. In areas reserved for conservation of native flora and fauna, control of blackberry infestations is a first step towards achieving an increase in species diversity. Reinvasion by weeds is a recurrent challenge therefore revegetation or pasture improvement strategies should be considered in tandem with any weed control program (CSIRO, 2011).
