Lucerne phase wears out weed seed bank
GroundCover™ Issue: 39
PERENNIAL LUCERNE is proving a very useful tool in the kit that WA farmer Stuart McAlpine uses to manage herbicide resistance in cropping weeds, as are other measures including seeding equipment that facilitates the application of a range of herbicides.
Speaking at the recent GRDC grains industry Adviser Update in Adelaide, Mr McAlpine said he had begun planting lucerne on his WA Midlands property in 1998 to provide grazing, mechanical means such as slashing and chemical options for controlling the weed seed bank. The lucerne also improves soil structure, and combats rising watertables.
He said he now had about 800 ha of lucerne on the 3,789 ha property in a three-year pasture phase attached to' the eight-year cropping phase. The property is in a 340 mm annual rainfall zone and soil types vary, although most are sandy loams.
"The initial 250 ba planting of lucerne returned to crop last year. These paddocks had some severe areas of ryegrass which had got out of control before the lucerne phase," he said.
Only one herbicide application needed
"During the pasture phase, grazing, slashing and spray-topping were used to exhaust the weed burden. In the 200 I season (when the paddocks returned to cropping), weeds were controlled with a single application of glyphosate at 1.1L/ha after the break of the season and just before seeding. This was the only application needed, as there wasn't another germination of weeds.
"This was a very pleasing result and has proved to me that a three-year ley is a good option to cut back weed seed reserves. At this stage I think three to four years of lucerne would suit, as it isn't cheap to establish and you need to recoup your costs. The length of the phase will ultimately depend on the weed problem and stock prices.
"I didn't have much trouble establishing it, or removing it when going back into cropping, but lucerne is pretty new to WA and we are still feeling our way."
Mr McAlpine said that on the property, where no-till farming and controlled traffic are practised, his Great Plains seeder is equipped with a coulter, followed by a double disc opener, followed by a press wheel. This allows for minimum soil disturbance but accurate seed placement.
This method had facilitated the application of two different knockdown herbicides - one after the break and the other just before crop emergence. He had also enjoyed success with trifuralin, with the coulters and press wheels disturbing enough soil to stabilise this herbicide.
He said he preferred this method to windrowing and burning to destroy weed seeds because there is too much danger of fire getting away and burning the stubble. "Stubble is too valuable in reducing wind erosion and retaining moisture."
In the future he hoped to separate chaff from the header and lay it on the tramlines in a concentrated trail where weeds, which germinated after the break, could be controlled by cultivation or spraying. There was also potential to map weeds at harvest with a GPS guidance unit so that small areas could be targeted before they became too large.
Program 6 Contact: Mr Stuart McAlpine 0427 642 082
Region North, South, West