Does organic farming have the answer to herbicide resistance?
Organic farmers do not struggle with the problem of herbicide resistance and they do not contribute to it.
However, they may know how to handle it.
Herbicide resistance is one result of herbicide overuse.
As an example, let’s say that one wild oat plant in a million is naturally resistant to a hypothetical herbicide called Annihilator. If Annihilator is applied in a field, the one resistant plant in a million has a much better chance of producing seeds than the other wild oats.
Read Also
Farming Smarter receives financial boost from Alberta government for potato research
Farming Smarter near Lethbridge got a boost to its research equipment, thanks to the Alberta government’s increase in funding for research associations.
The next year, there will be wild oat plants from seeds that were dormant during the spray year or from plants that emerged after the spray.
But many of the plants will be the offspring of the resistant plants in the spray year.
Perhaps in the second year, the resistant plants are one in a thousand.
The proportion of resistant wild oats increases in that field every time Annihilator is used.
The herbicide is a selection pressure: it selects against plants that are killed by the herbicide and for plants with resistance.
The weed population evolves herbicide resistance faster if the selection pressure is strong and consistent: if the herbicide kills most of the non-resistant plants and it is used year after year.
In a recent issue of this newspaper, weed scientist Ian Heap said that Canada has some of the worst herbicide resistant weed conditions in the world.
He used Manitoba as an example, where roughly half of the populations of the two most common weed species, wild oats and green foxtail, are resistant to common herbicide groups.
Weed scientists are exploring ways to handle herbicide resistance.
The short-term recommendation is to use a tank mix of two or more herbicides.
In the long-term, scientists hope that new modes of action will be found: new herbicides that kill weeds in new ways.
Does this make sense? Weeds are evolving resistance to herbicides, so let’s apply more herbicides and develop more herbicides.
If we continue with this old thinking, we will get the same old results.
This thinking shows that people can get locked into a narrow focus and be unable to see the broader picture.
The core problem is not that the herbicides aren’t killing the weeds. The problem is that the weeds are not well managed.
Too many farmers have become too dependent on herbicides. Producers and researchers contribute to the problem when they refuse to look beyond herbicides.
Weed scientists know this.
They advocate integrated weed management, which integrates the use of many types of tools, many of them not herbicides.
These are tools that expert organic farmers use, and it’s an area where organic farmers could provide leadership.
The research community has reassuring findings for farmers who are hesitant to take advice from organic producers.
Studies at the University of Saskatchewan and Agriculture Canada’s research center at Lacombe, Alta., indicate that “stacking” simple cultural weed management techniques can greatly reduce weed populations.
A diverse rotation is an ideal way to reduce herbicide resistance.
Every year is different, so the selection pressure each year is also different.
Late germinating weeds are selected against when crops are seeded early and provide strong competition by the time the weeds emerge.
Early germinating weeds are selected against when crops are seeded late, and a high disturbance seeder takes those early weeds out of the picture.
For example, winter annuals have a tough time competing with an overwinter crop such as fall rye, sweet clover or alfalfa.
A producer can avoid practices that give weeds a consistent advantage by matching rotations to weed problems.
Other techniques include:
• increasing seeding rates to 1.5 or two times the conventional rate can increase crop competition with weeds when herbicides are not used or when herbicides have lost their effectiveness;
• using cultivars with early vigour with quick establishment, quick canopy closure and leafy and tall growth can help give the crop the advantage;
• using a rod weeder or light cultivator after seeding but before crop emergence to allow crops to emerge in a clean field;
• using a rotary harrow in crop to eliminate small weeds;
• using chaff collectors to reduce weed seed return to the field for many weeds such as wild oats. Managing weeds without herbicides, or putting less emphasis on herbicides for weed control, requires more thought, and there can be a bit of a learning curve.
Organic producers have been working on this. Perhaps they can help.
Brenda Frick, Ph. D., P. Ag. is an extension agrologist and researcher in organic agriculture. She welcomes your comments at 306-260-0663 or email
