Australasian Association of Nematologists

A new weapon to combat annual ryegrass toxicity (ARGT)

George Yan & Ian Riley, Plant Pathology, Agriculture Western Australia, South Perth

Annual ryegrass toxicity (ARGT) is the poisoning of livestock from toxin contained in bacterially-infected annual ryegrass. The toxin is produced by the bacterium Clavibacter toxicus, which is carried into the ryegrass by a seed-gall nematode, Anguina funesta.

Much of the present ARGT management has focused on the control of ryegrass. Control reliant on herbicides is resulting in marked reduction in pasture productivity, is associated with a rapid increase in herbicide resistance and is often ineffective. Projects funded by GRDC and IWS have demonstrated that the naturally occurring fungus, Dilophospora alopecuri provides a useful level of control of ARGT without the need of controlling ryegrass. The fungal inoculum is now available to farmers for on-farm application.

The fungus reduces the risk of ARGT by hindering the movement of nematodes. Once inside the ryegrass, the fungus colonises the host and competes with the nematode and the bacterium. The effect of the twist fungus will be accumulative over the years. Results from field and pot experiments have shown that the fungus is capable of reducing the bacterial gall level by up to 100% and nematode gall levels by 50-70%, depending on the rate of application and conditions.

The fungus is found in parts of WA, SA and Vic. In WA, the fungus is most commonly found in the southern part of the state. The current distribution of the fungus in WA is believed to be a function of original introduction, possibly with Holcus lanatus. In the field, the fungus relies mainly on surface water flow and farm machinery for dispersal and spreads relatively slowly.

Use of the fungal inoculum will greatly accelerate the spread of the fungus outside its current range. To facilitate the establishment of the fungus, we are recommending that paddocks selected for treatment (1) have a history of ARGT, (2) have moderate to high density of ryegrass, (3) are likely to be in pasture in the following year. Our results have shown that spread of the fungus during the year of application is best with cropped paddocks. Harvesting and other activities will further spread the fungus around the paddock and farm. Hence, crop paddocks are better for local dispersal of the fungus. Paddocks that will be in pasture in the year after inoculation would assist the build-up of the twist fungus as it relies on the presence of a reasonable level of ryegrass.

The promotion, production and distribution of the fungal inoculum are currently funded by GRDC. The three year project starts from 1998 and aims to supply the inoculum to farmers to inoculate 10% of the ARGT-affected paddocks. We are now taking orders for the 1999 supply. If you are aware of anybody who is interested in the twist fungus, please advice them to contact G Yan on 08 9368 3935 or 08 9367 2625 (fax).