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Final Report
The project is to map the areas of the Upper Gilbert River Catchment infested with Giant Rats Tail Grass (Sporobulus spp.) and to predict the likely direction of the spread of the pest into the Northern Gulf grazing lands.
Milestones 1 & 2 produced a map of the known infestations of GRT in Etheridge Shire. Approximately 45% of the affected area had been surveyed by December 2009 and all of the target area was surveyed again in the period February 2009 to May 2009. The December 2008 map shows the affected areas in Etheridge Shire in the South on Black Braes NP, Lyndhurst, Oak Valley and Oak Park Stations and to the North on Rocky Springs, Abingdon Downs and Inorunie Stations. The area outside of Etheridge Shire is the major area of threat in the Mareeba Dimbulah area.
The outbreaks in the northern area of Etheridge Shire have largely been contained. The infestation information was gathered by a combination of landholder sightings and weed surveys. Extensive advertising and awareness programs were instigated as well as encouragement for vehicle and Machinery hygiene.
The threat to the Gulf grazing land at that time was predicted in the next map (Fig. 2) The direction of spread is from the affected areas in the south along the Einasleigh and Copperfield Rivers and eventually through the frontage country on both the Einasleigh and Gilbert Rivers. The spread of the weed through the Mareeba/Dimbulah district threatens the northern section of Etheridge Shire.
Further surveys and additional mapping indicates that GRT has a much stronger presence in the region than initially thought. It is also spread much further than has been anticipated. Fig.3 shows the locations of now known infestations.
GRT has been sighted on every river system in the Upper Gilbert River Catchment. The older infestation on the Copperfield River has been dispersed over the N-S arm of the Gregory Range and is in the headwaters of the Gilbert River. New sightings have been made on the Einasleigh common, Spring Creek Station and north of the Gulf Development Road west of Georgetown.   The predicted threat to the Etheridge Shire and the Gilbert River Catchment is shown in Fig,4.
Threat Description 1. The Sporobulus spp. sighted are mainly natalensis and fertilis and perhaps jacquemontii. Sporobulus pyramidalis has not been sighted in this region although it is the major GRT in the Mareeba / Dimbulah district. Pyramidalis is the sporobulus most likely to be introduced through fodder. 2. The GRT located has, in most cases, not adopted the characteristic aggressiveness that it is renowned for. The reasons for this are unclear however given that some of the infestations in the Upper Einasleigh and Copperfield Rivers could be more than twenty years old acclimatisation may not be the retardant. Hopefully the cause of the reduced effect of this pest will continue to restrict the spread of the GRT that has established in the catchment. 3. Control and Eradication of GRT is not probable. In most areas the weed is spreading as individual plants and it is very difficult to detect. Property owners are not likely to notice it in the course of their normal property management. 4. The introduction of GRT into the northern areas of the catchment poses a more serious problem because the climate is identical to that in which it has already established itself as a major pest in the hay growing area around Dimbulah. 5. Landholders should consider designing some form of property hygiene practice to reduce their risk exposure. Invitations to Prospectors, pig hunters, bird watchers, campers and fishermen should be offered with some sensible restrictions or conditions applied to them. Specifically insisting on vehicles being clean before they enter the property. Conclusion. Etheridge Shire was only threatened by GRT but it is now rated as infested with GRT. The spread of GRT will continue to invade most areas of the shire, albeit lightly and scattered, but it will establish plants across most of the shire. Eventually GRT will be present across most of the Gulf grazing landscape. How serious a problem it will become is not known but it has the potential to be catastrophic. This scenario is assured because too few landholders have actively managed their properties to prevent the spread of weeds to them. Visitors are unchecked, hay is rarely checked for noxious weeds, introduced stock is often not quarantined and awareness campaigns in local newsletters and mail outs have mostly gone unheeded Giant Rats Tail Grass is a real threat to the viability of the Northern Gulf grazing industry. Landholders should be planning now to deal with it and get procedures in place to reduce their risk of infestation.

For further information contact Allan Smith at the Etheridge Shire Council