Long-term control of serrated tussock (Nassella trichotoma (Nees) Arech.) by applying flupropanate at three-year or 10-year intervals
M.H. Campbell, D.T. Vere and H.I. Nicol, NSW Agriculture, Orange Agricultural Institute, Forest Road, Orange, New South Wales 2800, Australia.
An 18 month-old introduced pasture, sown in March 1994, infested with 8-18 month-old serrated tussock (Nassella trichotoma (Nees) Arech.) seedlings near Berridale New South Wales was sprayed on 6 September 1995 with low rates of flupropanate (0, 0.19, 0.37, 0.56, 0.75, 0.94, 1.12 kg a.i. ha-1) and monitored for serrated tussock and pasture species content until November 2000. Where no flupropanate was applied, the serrated tussock seedlings (53 500 ha-1 at spraying) increased from 5% ground cover in 1995 to 48% in 2000. Where rates of 0.56 kg a.i. ha-1 and above were applied, all seedlings were killed with only minor damage to the sown species. Use of 0.56 kg a.i. ha-1 to kill seedlings is a 62% saving on the rate generally recommended to kill mature tussocks. Re-infestation on the successful spray treatments did not occur until the second year after spraying and thereafter at a mean of 750 ha-1 year-1 or 1% increase in ground cover of serrated tussock per year.
Four methods of controlling re-infestation on the successful spray treatments with flupropanate were proposed (boom spray, fixed wing aircraft, helicopter, spot spray) and simulated at three-year and 10-year intervals. Re-treatment after three years with low rates of flupropanate was designed to prevent re-infesting seedlings from ever seeding and, re-treatment after 10 years with high rates of flupropanate, to remove the weed before it substantially reduced pasture production.
A benefit-cost analysis of the re-treatment alternatives over a 20-year period showed that boom spraying was the most economical option followed by aerial spraying with spot spraying the least economical and least efficient due to the difficulty of finding and treating all re-infesting tussocks. The 10-year interval treatments were more profitable than the three-year alternatives, except for spot spraying. It is suggested that repetitive overall treatment by boom or aerial application of flupropanate over long periods at three-year or 10-year intervals could economically control serrated tussock over large areas. These techniques also have the potential to control serrated tussock in some native grass pastures and to control other grass weeds susceptible to flupropanate.
Plant Protection Quarterly (2002) 17 (2) 58-63.