Bacterium hope for ryegrass control

By Graeme Jennings

A new biological agent is showing promise as a non-chemical control of annual ryegrass.

A team at Charles Sturt University (CSU) in central NSW, is working with a bacterium that weakens the ryegrass enough for the crop to become the dominant presence.

In glasshouse trials the bacterium has reduced ryegrass root growth by 80 percent and increased the root development of wheat by 20 percent.

Dr Gavin Ash, Associate Professor in Plant Pathology at CSU, says it gives the cereal a competitive advantage over the weed so the crop, in effect, becomes the control agent.

The CSU team is working on a formulation that will allow the bacterium to be applied as a seed dressing or drilled in at sowing to help the crop out-compete ryegrass.

The potential ryegrass control is just one of a suite of biological controls being developed, or already in use, as new non-chemical insecticides, herbicides and fungicides.

Work is also underway on a Phomopsis fungus that kills saffron thistle, capeweed, Bathurst and Noogoora burr, fireweed and bitou bush, a major environmental weed in southern Australia.

In the right conditions it can kill saffron thistle in four days, but needs cool moist conditions to build up in the field so it is unlikely to be a control option for summer-growing weeds or weeds in dry regions, Dr Ash says.

The researchers are working on how to store and apply the organism and on ways to increase its efficacy in the field. Use of the fungus with complementary low rates of herbicide (as little as one percent of usual doses) is showing considerable potential.

“These results indicate scope to reduce the chemical load in the environment, reduce the risk of developing chemical resistance in weed populations and minimise the risk of chemical contamination of water resources,” Dr Ash says.

The CSU team has also identified a bacterium that appears to have the potential to control blackleg in canola by triggering the resistance mechanisms of the plant, thereby preventing infection by the blackleg fungus.

Yet another dimension of the innovative “biological pesticide” work being done at CSU - much of it funded by the Australian Research Council - is control of slugs and snails by a bacterium carried by nematodes.

In Queensland, where there is more summer cropping and concern about resistance in heliothis, much of the bio-pesticide focus has been on control of heliothis in cotton and corn.

Queensland Department of Primary Industries and Fisheries principal scientist Caroline Hauxwell leads that work, which has now expanded from heliothis into other areas - including microbes to control sucking pests such as mirids and diamondback moth; a major pest of horticultural and broadacre Brassica crops.

Dr Hauxwell says the organisms the Queensland team are working with are pathogens that are specific to the target pest. Therefore they are "soft" on the environment, having no impact on other insects, especially beneficial predators or parasites that control the target pest.

“Using a chemical often knocks out beneficials and creates a pest problem rather than preventing one,” she says.

“A microbial control agent doesn"t cause a build-up of resistance and doesn"t disrupt the populations of natural control agents, avoiding the flaring of pest populations that can follow application of a hard chemical.”

In other areas, the GRDC"s Soil Biology Initiative is exploring the use of micro-organisms to control cereal root diseases such as rhizoctonia, pythium, crown rot and take-all.

Greg Bender, who is co-ordinating the $10 million, five-year Soil Biology Initiative, says researchers have identified indigenous organisms that can control cereal root disease. However, not all of them work consistently in all environments, and not all are yet suitable for commercialisation.

For more information:
Gavin Ash, 02 6933 2765,
Greg Bender, 02 6248 0165,
Caroline Hauxwell, 07 3896 9362,

Region North