This has been particularly devastating in Australia where moisture conservation is vital.
The objective for New Zealand farmers must be to put weed seedbanks into decline while herbicides are still effective.
“We live and die on how we store water and glyphosate is the key to controlling weeds in non-crop periods in order to store moisture.”
Widespread herbicide resistance is now dictating farm systems, crop rotations, and management and there are few new herbicide modes of action in the pipeline to relieve the situation.
Cameron said most paddocks in Australia will have one or more weeds that are resistant to one or more herbicide modes of action.
Cautioning farmers in this country, he said every herbicide application moves the weed population towards resistance.
In Cameron’s opinion more herbicides were not the solution – non-herbicide options must be added to the system.
The objective for New Zealand farmers must be to put weed seed banks into decline while herbicides are still effective, he said.
“What we should have been doing, when herbicides were working for us, was to work out how to reduce our weed seed resistance.
“The challenge for you is to use herbicide to best effect while they are still effective.”
In Australia this means the adoption of non-chemical methods to control weeds including competitive crops, topping crop and pastures weeds to prevent seed-set, patch management, tillage, silage and hay crops, and fire.
Small reductions in the seedbank all add up, he said.
From left, Nick Pyke (FAR), John Cameron, and Nick Poole (FAR) at the Foundation for Arable Research conference in Palmerston North in July. John Cameron urges farmers to use herbicides to best effect while they are still working.
Australian consultant John Cameron explained at the FAR conference that herbicide resistance was simple maths.
In ryegrass, for example, before farmers even start using herbicides there will be genes in that grass population that confer resistance.
So if one plant in 20,000 has a resistance gene and 10% of weed seeds are not killed by herbicides then in year two one-in-200 plants will have the resistance gene. In year three it will be one plant in 10, and in year four it will be one in every two plants.
Once farmers have resistance on their farm they are not able to dilute that resistance.
“When you use a herbicide you are ratcheting that population closer to resistance,” he said.
