Herbicide resistance is an increasing threat for the New Zealand arable industry. A number of weeds are becoming harder to kill particularly wild oats and Italian ryegrass in Canterbury.
Herbicides act by interfering with specific plant processes, how they act is known as their mode of action. Herbicides are categorised from A through to Z depending of their specific mode of action group. This is based on the HRAC classification.
Herbicide resistance evolves following the intensive use of herbicides for weed control. Factors that affect the evolution of resistance are frequency of use (how many applications or the number of years of herbicide use), mode of action (Group A have a higher frequency of resistance than Group N), weed biology and density (weeds that produce large numbers of short seed life seeds develop resistance faster).
To reduce the risk of herbicide resistance: rotate between mode of action Groups across years, calibrate equipment and apply herbicides to recommended label rates, keep accurate herbicide application records for each paddock.
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