Weed management - Serrated tussock strategy pays off
A 20-year serrated tussock control program is one of the factors that has helped Murray and Barbara Stephenson double the carrying capacity on ‘Brooklyn’, at Binda, near Crookwell, NSW.
When they bought the farm 25 years ago the weed was identified, but the extent of the problem was not realised until five years later, when it had spread rapidly across the 340-hectare property. It was only then that they realised it was such a prolific seeder, with new infestations rapidly occurring downwind from existing stands, or on land where soil had been disturbed.
However, today the property has only isolated patches of serrated tussock, due to the Stephensons’ diligence.
The greatest impact of the serrated tussock infestation was on the carrying capacity of ‘Brooklyn’. Where the weed was not controlled in the past, Murray estimated there was a large reduction in the stocking rate, as the weed competed with both introduced and native pastures. Today ‘Brooklyn’ carries 1700 Merino and first cross ewes, producing 1700 lambs a year.
Little information was available about control methods when serrated tussock was first recognised as a problem and the Stephensons’ approach was largely based on trial and error. They originally wanted to achieve maximum impact to control serrated tussock, and so their first approach was to plough out the weed from the worst-affected areas and introduce improved pastures, including clover, cocksfoot and ryegrass, in the hope that these would out-compete serrated tussock. Unfortunately, ploughing and cultivation encouraged the weed to spread further and the pasture species could not compete.
Murray and Barbara soon learnt that it was necessary to treat the weeds with herbicide during the pasture-establishment phase.
Serrated tussock also infests native pasture on ‘Brooklyn’, and in these places Murray and Barbara have relied on herbicide.
The Stephensons have undertaken two key phases of the control program.
For the first 15 years, they undertook an intensive spot spraying and pasture-improvement program, requiring about two weeks of full-time labour each year. This largely eradicated the larger patches of serrated tussock and reduced the number of new seedlings.
Over the past five years, Murray and Barbara have been able to scale down their control program. Murray now spends only two days a year spot-spraying any new seedlings, with a focus on those parts of the farm where the soil has been disturbed. Their control strategy relies on herbicide treatment, complemented with competitive pastures. Cultivation is now used only to establish improved pastures and not as a tool for serrated tussock control.
The preferred method of control for serrated tussock is the application of fluproponate, which in Murray and Barbara’s experience has been superior to glyphosate.
Murray and Barbara have learnt over time that the key to success with herbicide is to allow pastures to gain a competitive advantage over the sprayed weed. They believe there are two critical tactics to achieve this:
- spray serrated tussock when pasture species (improved or native) are dormant; and
- spot-spray weeds to avoid chemical damage to surrounding pastures.
Murray uses a novel approach in his spray application for serrated tussock: a modified drench gun to apply a metered dose to each tussock plant. Because the spray is targeted to the base of the plant, it has minimal effect on the surrounding pasture cover, helping to reduce the area of bare ground on which serrated tussock seed could germinate.
Ensuring pastures retain their vigour is also important. For the introduced pastures, fertiliser is applied at rates based on soil test results. This averages about 125 kilograms per hectare of single superphosphate per year. For the native pastures, about every five years Murray excludes stock in late spring to allow the pastures to set seed.
The control program implemented on ‘Brooklyn’ has allowed grazing capacity to double over the past 20 years, thereby improving farm profitability.
Given that the carrying capacity has risen from 3.5 dry sheep equivalent per hectare (DSE/ha) 20 years ago to seven DSE/ha today, the return from each hectare of the farm has essentially doubled. Based on an estimated gross margin of $40/DSE, Murray has, over the past 20 years, increased annual returns by about $140/ha.
In addition, Murray says that the value of the farm has also increased, now that it is relatively free of serrated tussock.
Over the past 20 years, Murray and Barbara’s experience has taught them several key lessons that they would pass on to other producers facing the same problems with serrated tussock:
- be vigilant – watch for new plants germinating and act quickly;
- apply chemicals to tussock plants only – if spray affects the surrounding pasture species, their vigour and competitiveness is reduced, thereby reducing the effectiveness of weed control; and
- chemical concentration can be quite low, and therefore cost-effective, if spot spraying is undertaken at the right time and applied correctly.
More information: the new set of 3D guides is available from the AWI Helpline on 1800 070 099
Image: ‘Brooklyn’, Binda, where the Stephensons have concentrated on weed management.
See also: Weeds need strategic attack
Return to Beyond the Bale Issue 28 index page.