Controlling serrated tussock along Jacksons Creek: post grassfire, Riddells Creek

  • Ivan Carter
  • VSTWP Extension Officer

Heather and Mike have been farming on their rural property near Riddells Creek in Victoria, one hour north of Melbourne, for a few decades. The property adjoins Jacksons Creek and consists of fertile river flats and dark loam soils, lending itself to some productive farming. They ran some stock on the rich pastures of the river flats and had mostly been dealing with Gorse and Willows during the early days on the property. They have seen their share of droughts, floods and good times on the small farm, but never had they experienced a grassfire tear through the property at great speed.

Mike has noted that serrated tussock was most likely introduced to the property during the drought years in the early 2000s, but at that time was not an issue as it was low in density and difficult to distinguish amongst the pastures and native Poa species in the area. The local landcare group ran a series of workshops on identifying invasive plants in the region and the local government had also been alerting landowners to the serrated tussock infestations that were establishing in the area, but Mike and Heather did not confirm that they had serrated tussock on their property until just prior to the grass fire in 2014.

Following the devastating grassfire in early 2014, Mike and Heather noticed that one plant species in particular was growing back vigorously and that many seedlings had germinated in the bare soils following the hot fire. Mike was visited by local and state government representatives, who all identified the plant species to be serrated tussock. The established plants present prior to the grass fire were recovering vigorously and new seedlings were germinating over the most productive parts of the property, in medium densities. Mike recalled that he first observed what he now knows to be serrated tussock on the property from around 2010, but at that time presumed it was a native pasture species, so did not treat it during the early stages of spread.

In the winter of 2014 the Victorian Serrated Tussock Working Party (VSTWP) held a local serrated tussock information day, which Heather attended to learn more about combating the large infestations on their farmlet. An inspection was arranged with a VSTWP Extension Officer in late winter, with Mike and Heather walking over the property with the Extension Officer, to discuss the best way to manage the 500 odd plants that had germinated or recovered after the fire. The infestation covered around 50% of the farmlet, with densities ranging from low scattered sites, to high density areas along the river flat.

The VSTWP wrote a management plan for Mike and Heather that suggested they work on spot spraying the germinating and recovering plants prior to seeding in late Spring 2014. The VSTWP Extension Officer mapped all infestations for Mike and Heather, and provided an aerial map with the infestations marked. The medium term plan will be to improve the pastures across the arable areas of the property, minimising further germinations of serrated tussock plants and providing a competitive break against further infestations.

The key message is that spot spraying is really the most selective tool available so it is critical that paddocks containing scattered serrated tussock are treated early and never allowed to reach the stage of a dense infestation. Once paddocks, particularly non arable areas containing native pastures become dominated by serrated tussock, there are no straightforward, low cost solutions available. Mike and Heather concluded that if the serrated tussock had not been identified and treated immediately after the fire in the coming years the farmlet would be swamped by massive seeding and dense infestations, particularly given the bare ground and areas with little pasture competition. Longer term management of the farmlet will involve regular spot spraying and manual removal of plants every spring and autumn, and establishing a ground cover of desirable species and pasture improvement.

The farmlet is now at a stage where stock have been reintroduced and pasture has recovered on most of the bare ground, with little or no serrated plants being allowed to seed after the fire. The case study has shown that nearly all of the serrated tussock plants partially or fully recovered after the fire, despite many landowners believing the plants would have been killed by the extreme heat. Mike said “we are noticing that many of the burnt serrated tussock plants are regrowing from their base, and new seedlings are emerging on the scorched ground between the regrowing plants, so we will monitor these in 2015 to evaluate our success in treatments”. Following a fire, weeds often re-establish more quickly than desirable pasture and native species, and can rapidly dominate the landscape.

Landowners should also note that fire can interfere with previous treatment programs by reducing the effectiveness of any residual herbicide in the soil.