STRATHMORE, Alta. – Herbicide resistance in weeds is an international problem with more cases confirmed each year.
Cleavers in central Alberta showed resistance to Group 1 herbicides and earlier this month, wild oats with resistance have been confirmed in southern Alberta sugar beet fields, said provincial weed specialist Linda Hall.
Reports from Australia indicate a type of ryegrass has multiple herbicide resistance including the ability to stave off glyphosates such as Roundup.
“It is not impossible that we are going to get Roundup resistance, but it is still quite unlikely compared to our bigger problems,” said Hall.
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Herbicides attack weeds in different ways. They are grouped according to their mode of action and there are 26 groups.
When a farmer sprays a field, about 80 percent of the weeds die. The survivors include plants genetically capable of surviving the effects of the herbicide. Those plants produce seeds, so each year more resistant plants are detected.
The resistance problems are often found in fields farmed by those who consistently use pesticides and enjoy high producing crops, said Hall.
“They’re our best producers. They’re the ones who did what the extension people told them to do to control their weeds,” she said.
Many herbicides attack a plant in a specific way, such as inhibiting cellular division or attacking specific enzymes. Resistant plants appear when farmers repeatedly apply herbicides that kill in similar ways. If a farmer uses a herbicide for five years before switching, resistance is likely to appear, said Hall.
Reduced tillage is another factor contributing to the spread of resistant weeds. In minimum and zero-till farming, farmers stopped using cultivators and weeds weren’t plowed under.
Most farmers don’t notice a problem until the infestation covers 10 to 30 percent of the field, said Hall.
Herbicide resistant canolas and wheats could pose another problem. They may sow volunteer plants the following year.
To delay the spread of resistant weeds, Hall said: “When you have a good thing, don’t stick to it.”
Rotate weed control methods. Selective tillage can root out problem weeds. Other control methods include seeding hay crops, grazing and increasing seeding density so competitive plants choke out weeds.
Hall recommended farmers keep a herbicide history for each field.
Farmers who live in an area where herbicide resistance has been detected, should be particularly vigilant.
