From http://biodynamics.net.au/problems-with-bathurst-burrs/
We were recently tweeted asking how to deal with the problem of bathurst burrs and two of our directors have suggested solutions and these can apply to any weed problem you might be experiencing.
Director Shane Joyce suggests the following:
This is the methodology I use for any weeds.
1. Apply full biodynamic preparations (soil activator) 3 times, each a month apart, at 2 days prior to moon opposition saturn. However do not let the astro thing get in the way of just doing it at any time!
2. Collect a good quantity of the bathurst burr (fill a 200 litre drum & then fill with water & allow to ferment for a month. Use this liquour at a dilution of 10 water to 1 of liquour & apply to land. Can be added to biodynamic preparations when applying them at around 3 litres per hectare.
3. Collect seed from Bathurst burr & make a pepper & apply this to land.
The reasoning behind the steps 1, 2, 3. First work on fixing the soil, second work on magnifying the “influence” that the weed is trying to bring in to repair the soil, & last of all use peppers to work on the fertility/flowering/seed set of the weed.
I believe Bathurst burr is a “silica plant” so a good idea would be to use horn silica in the biodynamic preparations that are applied.
Director, Hugh Lovel adds to this:
Bathurst burrs thrive on compacted land that has degraded and is low in calcium as well as a variety of trace minerals which generally include sulphur, boron, copper, zinc and manganese, but can also include cobalt and molybdenum.
Find the cause or they will be back, and if not Bathurst burrs, something worse. Apply preparations accordingly to repair the land.
As Shane suggests collect a cupful or so of seed and burn these to ash near full moon in a fire sign and collect the ash. If there a few contaminants (not seeds of plants you want) it doesn’t matter much.
Dilute and potentize in series, each one part in ten with water from the previous potency, from D1 to D6. Spray the D6 around the affected areas, again prior to full moon.
Repeat as necessary.