5 Nov 2024. Paul McIntosh, Pulse Australia and WeedSmart.
The photo might look fairly mundane, however that soil is what is going to grow our food and fibre crops for years, or hopefully many decades, to come. Therefore, looking after our arable land is very important. A major part of these custodial role duties is for our professional farmers and their agronomic advisors to take charge of.
Image: Our extremely important healthy top soil.
Maintaining our soils outputs is a complex management job including nutrition, soil health and disease, plus the all important weed control tactics to be decided upon.
My article direction today is on some of the residual herbicide tactics, that we definitely will be needing to strategically use more in the future and this will have a major bearing of protecting our soils from water or wind erosion. Add onto that is the ability of our soils to adsorb and retain moisture for our future cropping programme in this desirable stubble retention weed-free system.
All our residual herbicides have a solubility rating which indicates how much herbicide can dissolve in water. For a very old grass residual herbicide like Trifluralin, it is not very soluble at all and needs mechanical incorporation or mixing in the top soil with harrows or light cultivator soon after application. No sense waiting for rain or irrigation to do this incorporation job as the herbicide is not very soluble and also will volatilise.
Moving to the other end of the scale is an old herbicide like Picloram. Picloram has been used for many broadleaf cropping weeds and also in non crop areas of lantana, tree of heaven, box thorn, parthenium, rubber vine and the list of bad ones goes on. A valuable product it has been and still is.
Now Picloram from the original old Dow Chemicals Tordon line is very soluble and can penetrate into the top soil with a small shower of rain soon after application. This makes Picloram have some good residual activity on pesky weeds like Sowthistle, Datura or even errant Mungbean volunteers.
Next we add into this soil explanation and we consider binding or adsorption coefficients. Once again the old Trifluralin herbicide can bind tightly to organic carbon or soil particles with a high Koc value and stays at the depth generally where it was incorporated to.
Picloram does not bind to soil particles or organic matter very tightly at all and can move around with soil moisture or wetting fronts.
All of our residual herbicides may have these performance idiosyncrasies attached to them. With herbicide resistance on the increase, extra knowledge about the ecology of our plants of place, along with various herbicides properties, allows us to choose and apply a suitable spray option for a more successful long term farming environment.
That’s all folks.