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Herbicide Resistance

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.

For more information, please click the following links:

Arable Extra 114, Group B herbicide resistance in ryegrass

Arable Extra 109, Have wild oats in Canterbury become resistant to herbicides?

Herbicide Mode of Action Table

Guidelines for minimising the development of glyphosate resistance in weeds in arable and vegetable crops

Guidelines for minimising the development of glyphosate resistance along fence lines and field margins

New Zealand Plant Protection Society - Resistance information

Herbicide resistance testing option