Biological control of giant Parramatta grass
24 Jun 2013
A new biological control is successfully fighting back against pasture weed giant Parramatta grass (GPG), with researchers now upping the ante by developing more efficient methods of spreading the naturally occurring fungus.
It’s estimated that GPG and other weedy sporobolus grasses are found across almost half a million hectares of Australia’s east coast, costing graziers some $60 million in lost production.
But farmers are now fighting back, thanks to recent trials which have proved both the effectiveness the fungus Nigrospora oryzae and how it can be safely spread into GPG infestations.
New South Wales Department of Primary Industries (NSW DPI) research agronomist David Officer has overseen the trials, which have been supported by funding from the National Weeds and Productivity Research Program, managed by the Rural Industries Research and Development Corporation (RIRDC).
“Until recently, graziers have had to rely on chemicals that are expensive and often provide only short-term suppression,” Mr Officer said.
“We’ve discovered that N. oryzae is a highly effective control method for weedy sporobolous grasses, causing a type of crown rot which can reduce infestations to manageable levels over a 2-3 year period.
“Trials in northern New South Wales have shown that N. oryzae can be easily spread by re-locating grasses carrying the fungus into the midst of an un-affected infestation.”
These trials are now being replicated in southern Queensland and southern New South Wales, as weedy sporobolus grasses have spread into these areas over recent years.
Mr Officer has also produced a video showing graziers how to identify and transplant the fungus, which is best done in spring and summer when the leaves of affected plants turn bright orange. The video can be found on the RIRDC YouTube channel (http://youtu.be/M8g96eYvcVs).
“What we’d like to develop is an effective way to spread the fungus without having to dig up plants to move the fungus around,” Mr Officer said.
“The current technique used to grow the spores in the lab to spray on plants as part of the trials is very labour-intensive and not suitable to produce large quantities needed for commercial release.
“This season for the first time we’ve been able to inoculate sterile grain with the fungus. The grain provides a food source which helps to keep the fungus alive longer than in the liquid solution and can be spread in the field like a solid fertiliser over weedy sporobolus infestations.
“Once the technique’s perfected, it’s hopefully going to provide a quick and cost-effective way of providing bio-control over large areas in the field,” Mr Officer said.
NSW DPI has a fact sheet, Nigrospora crown rot for biocontrol of giant Parramatta grass, available on its website at www.dpi.nsw.gov.au/factsheets. More details about the National Weeds and Productivity Research Program are available at www.rirdc.gov.au/weeds.