Application, spray rate key to weed control

There has been a distinct shift in the spectrum of weeds seen on farms across Australia toward species, such as fleabane, sowthistle, feather top Rhodes grass and skeleton weed, which have a natural tolerance of herbicides.

Bill Gordon, spray application consultant with Nufarm Australia says these ‘hard-to-kill’ species often have hairy surfaces, thick cuticles, reduced translocation due to plant stress or internal mechanisms that metabolise the product. 

“The application rate and technique are critical when managing these weeds,” he says. “If the application is compromised there is a good chance that the weed will survive and go on to set seed.”

What are the common spray application mistakes that can contribute to herbicide resistance?

Application technique and the choice of product, rate, water volume and adjuvant are generally within the grower’s control. Weather conditions and the plant size and stress are harder to work around. In ideal conditions the aim is to apply the right rate of the right product to the right target to achieve plant death and prevent seed set. 

How does stubble affect the dose delivered to the target weed?

Standing stubble can intercept many droplets before they reach the target weeds. Choose an appropriate spray quality for the target and the mode of action. Use visual indicator tools such as water sensitive paper to ensure adequate coverage is achieved where it is needed. 

How can I counteract the edge effect to apply the correct dose on paddock borders?

Maintain wide enough headlands to allow easy turning and entering the paddock with the full spray pressure. Using a minimum hold in the controller for non-residual products will prevent the rate dropping too low and ensure the nozzle’s spray pattern does not collapse.