Australia
January 16, 2006
Innovation in weed control has become essential in Western
Australia, where herbicide resistance can mean severe loss of
productivity.
“The use of chemicals is becoming less sustainable,” says Sally
Peltzer, research scientist at the
Department of Agriculture
in Albany. “There’s a need for more innovative, non-chemical
ways to control weeds.”
Dr Peltzer says farmers now have fewer post-emergent herbicide
options. “Because of herbicide resistance and the subsequent
increase in the weed seed bank, they now have to consider their
rotations and weed strategies and plan several years ahead.”
Dr Peltzer, in collaboration with Dr Gavin Ash of Charles Sturt
University in New South Wales, has begun a new GRDC-funded
project in the use of natural bacteria to control annual
ryegrass. Annual ryegrass is a common agricultural weed which
has developed a resistance to nine major herbicide groups in WA.
It also presents a livestock problem due to annual ryegrass
toxicity.
Deleterious rhizobacteria (DRB) are root-living bacteria that
inhibit plant growth. These are naturally occurring bacteria
which can be very plant-specific, minimising the risk of harm to
non-target plants. Isolating bacteria that affect weed growth
but not crops is the key to the project.
“The technique is to use large quantities of bacteria to ‘bomb’
the weed with,” says Dr Peltzer.
This approach overwhelms the weeds after germination. In the
summer, the bacteria revert to naturalised numbers and must be
applied again in subsequent years.
This method differs from traditional biological control, which
relies on the introduction of low numbers of an exotic organism
which then spreads through reproduction.
The new approach can achieve weed control in the year of
release, whereas the standard approach can take a long time and
includes the risk of attack of other plants.
Dr Peltzer hopes to use the technique in conjunction with
increased cropping rate techniques, such as sowing wheat at 120
kilograms per hectare in problem paddocks.
“Increasing crop competition means crops have a greater chance
of out-competing weeds. Used in conjunction with the bacteria we
hope to see high levels of weed control,” she says.
“Each technique on its own might prove 40 per cent effective.
Used together, we should achieve a much greater success rate.”
In 2004, Dr Peltzer spent research time in the USA where DRB has
been trialled for over 10 years.
“In the US, there are a multitude of weed species in their crops
(8 major ones in the mix is common) and targeting one or two
species at a time using DRB does not necessarily work as the
other 6 take over,” she says.
“In Western Australia, where there is usually only one or two
major weed species present in crops, it’s easier to use
biocontrol.”
Dr Peltzer hopes that at the end of the three-year project there
will be a commercial application for this biological weed
management technique. It is likely that the bacteria can be
granulated for application at seeding time.
A
report last year estimated that weeds cost Australia $4 billion
per year in lost production and control programs. An integrated
approach to weed management is the most sustainable solution for
land holders.
“No one technique is the solution,” says Dr Peltzer. “Integrated
weed management should include a combination of chemical,
cultural, physical or biological techniques, for example these
bad but good bugs” |