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”