Lippia, like several of our worst weeds including blue heliotrope, is commonly found in gardens, often deliberately planted for beauty or in the case of lippia as a hardy lawn species.
Recently I stayed in Broken Hill and noted Lippia was successfully established in this dry environment as a hardy plant in our gravel courtyard.
No doubt many people marvelled at this successful lawn and maybe unwittingly helped it spread across the nation via seeds and plant fragments that may lodge in tyres or on shoes.
Lippia is a deep-rooted perennial and is especially a weed of flood-prone areas and infests several million hectares of NSW.
It is regarded as near useless for feed and crowds out pasture. It is easily spread by floods and cultivation and suits a range of soils.
Research some years ago in the mid-Lachlan flood plains showed lippia can be combatted by a combination of strategic herbicide combined with competitive pastures.
NSW Department of Primary Industries (DPI) trials noted 2,4-D amine was one herbicide that controlled lippia in a pastoral situation and did not harm most grass species, but it is not really an option in cotton areas.
Pastures where 80 per cent of groundcover was lippia dominant sprayed with two litres a hectare of 2,4-D Amine 500 plus 1pc petroleum crop oil controlled 80-90pc.
A second spray the following year increased control to better than 95pc. A third spray the next year controled 99pc or better.
Research leader and then Forbes DPI district agronomist, the late Ken Motley, said it was important to spray only after reasonable summer rains.
Removing lippia vastly improved grass pasture growth with stocking rate improvement from 1-5 dry sheep equivalents a hectare.
Mr Motley showed introduced tropical species like bambatsi panic and Premier digit was especially competitive against lippia, but were mainly only an option on arable country able to be cropped. It is preferable to crop such areas for at least two and preferably three years before sowing down to pasture.
Summer fallow management that ensures all lippia and other summer herbage are killed and prevented from seeding, over three years, goes a long way to depleting the weed seed bank and maximising the chance of successfully establishing a tropical grass pasture.
Fallow weed control also allows for a greater range of herbicides to kill lippia. Ploughing can contribute to spread as plants can establish from plant fragments.
- Bob Freebairn is an agricultural consultant based at Coonabarabran.
- Email robert.freebairn@bigpond.com or contact 0428 752 149.
