Monday, 16 March 2015
Banish Brushweeds as autumn growth takes root
Early autumn is an ideal time to control brushweeds, because herbicides work best when weeds are actively growing and soft, new growth is present.
There are a number of herbicides that will control brushweeds, if used correctly. The best one to use depends on a number of factors such as the brushweed species present, the stage of development of the block and the importance of selectivity to pasture species.
Triclopyr mimics auxins; plant growth regulation hormones. It is mainly absorbed through the leaves and stems and moves within the plant to interfere with cell division and elongation. You can observe physical symptoms a few days after application, as weeds’ leaves twist and contort. Ravensdown’s Eliminate is based on tricolpyr.
Like triclopyr, picloram mimics auxins to cause rapid cell division, but picloram is more readily translocated in the plant. Both triclopyr and picloram are regarded as being grass friendly, but will kill clover in treated areas and picloram will have a longer residual effect on the re-establishment of clovers. Ravensdown’s Eliminate Brushkiller is based on a combination of triclopyr and picloram.
Metsulfuron inhibits amino acid synthesis: preventing cell division in the shoots and roots of the weed. It is active at low rates, but does damage many productive pastures grasses and clover.
However, browntop is tolerant to metsulfuron, so in areas where browntop is prevalent in pastures, it can be a good option. Metsulfuron is also a lower cost option, so the money saved on herbicide can be used to build up fertility in the soil to prepare the ground for more improved pasture species at the same time as controlling the brushweeds. Browntop can be surprisingly productive when soil fertility is improved. Eradicate 600 is based on metsulfuron.
Many weeds, including gorse and broom, have thick, waxy cuticles which act as a barrier to water-based particles. For best results, brushweed herbicides should be used with a good-quality organosilicone penetrant, such as Accelerate. Accelerate drastically reduces the surface tension of water droplets, allowing them to flood through the stomata - tiny holes that cover the surface of leaves, as well as aiding penetration through the waxy cuticle of the plant.
It is important to take a programmed approach to weed control. Good fencing and plentiful water supply is required for grazing management, which is an essential part of controlling seedlings. Follow up the initial spray-out with spot spraying to keep the block clean. In badly infested blocks, it can be advantageous to go through one or more shorter rotation pastures or crops to get the brushweeds under control and allow time rectify any soil fertility issues, before attempting to establish longer term pastures.