Your Reading List

Australia tackles herbicide resistance

Farmer Down Under are looking to mechanical weed control 
to deal with herbicide resistant weeds

Combine in a field.

The expensive and time consuming weed control measures most Australian grain farmers are facing should stand as a clear warning to western Canadian farmers not to take the issue of herbicide resistant weeds lightly.

Australian weed researcher, Michael Walsh, recently speaking to prairie farmers at the FarmTech Conference in Edmonton, made it abundantly clear if herbicide resistance ever gets out of hand, it literally threatens the economic-life of crop production. Walsh showed a map of the country, which has 61 million acres of annual cropland, covered with red stickpins identifying farms affected by herbicide resistant weeds over the vast majority of seeded acres.

“We got to the point, after 30 years of conservation farming, and 30 years of development of herbicide resistant weeds where we had to ask ‘with so much resistance is that the end of crop production in Australia?’” says Walsh. “We couldn’t rely on herbicide control of weeds so our options were greatly diminished.”

For the past 15 to 20 years Australian farmers have been gradually clawing their way back to some manageable level, resorting to a range of mechanical weed control measures at harvest. Fire is also used to some extent to burn weed-seed laden chaff windrows and piles. Because of the risk of serious soil erosion, tillage is seen as a last-ditch option.

A wide range of tools 

Herbicide resistant weed management has become a multi- pronged approach for Australian producers — proper crop rotation, a proper rotation of herbicide chemical groups where they work, and mechanical measures that includes collecting chaff (and weed seeds) at the combine for burning, baling and removing chaff from the field, and a $240,000 unit that crushes and destroys weed seeds at the back of the combine. All these measures haven’t eliminated herbicide resistant weeds, but make the problem somewhat manageable.

“The problem developed because we had very effective and relatively low cost herbicides and farmers kept using them repeatedly,” says Walsh. As well, to reduce costs instead of spending $20 per hectare on herbicides, some producers cut the rate to $10 per hectare — a move that just hastened the selection of herbicide resistant plants. The herbicides were effective and made good economic sense for a while, but through years of regular use, herbicide resistant weeds began to appear and rapidly spread.

While they have multiple weeds resistant to herbicides, the main yield robbers are wild oats, wild radish and annual rye grass. “These weeds have adapted so well to growing conditions,” he says. “They are aggressive and often they stand above the crop canopy so there is no way to avoid them at harvest.” They found cutting a crop with a 15 inch stubble collected about 30 per cent of the weed seeds, while leaving a four inch stubble collected about 80 per cent of the weed seeds.

As farmers and weed specialists looked at the herbicide resistance issue, they realized in the absence of no or fewer in-crop weed control tools, they could perhaps tackle the problem by first reducing the amount of weed seed going back on the land to re-infect next year’s crop. “We found that 80 to 90 per cent of weed seeds could be collected in chaff by the combine, so we looked at ways to intercept weed seeds at harvest,” says Walsh.

This slideshow requires JavaScript.

Mechanical measures

Working with farmers, one of the earliest tools tried in the 1980s was a chaff-cart collector. They worked with all makes and models of carts, and one Australian producer, Lance Turner, built a system that included a chaff cart fed by a conveyor system from the back of the combine.

The chaff cart collected weed seeds, but the issue became what to do with the chaff piles. The chaff can be fed to livestock, but if farms had no cattle the chaff piles had to be moved. They are light, hard to pickup and trucking costs are high. Many are just burned.

In a similar vein, other producers designed a chute system for the back of the combine, which deposited chaff on the ground in a 20-inch windrow. Again, these windrows had to be burned.

“I understand that burning on this scale in Canada isn’t an option,” says Walsh. Although allowed in Australia, it is not a perfect solution. Burning conditions have to be right to avoid causing widespread stubble fires, the piles and chaff rows are slow to burn and smoulder for days, and manpower is an issue too. Under reasonable conditions, four men can set fire to chaff windrows on 1,000 acres per day.

Another option tried involved baling chaff and weed seeds directly as they came off the back of the combine. It can be done, but there is a limited market or use for baled chaff, so that option has limited appeal.

One of the better options, still with limited use, is a machine known as the Harrington Seed Destructor. It was adapted by a farmer familiar with crushing mills used to crush coal into powder. Chaff and weed seeds are fed by conveyor into the portable mill, pulled behind the combine. The mill is driven by a 200 horsepower gas engine.

While it took several modifications, Walsh says they now have a working model, worth about $240,000 per unit, which is effective in crushing and destroying 90 per cent of weed seeds collected by the combine. Straw is chopped and blown off to the side by the combine. The Harrington Seed Destructor will be demonstrated in Canada in 2014.

Making progress

Use of mechanical weed control tools isn’t perfect but it is helping, says Walsh. Studies show, on average emergence of rye grass weeds was reduced by about 57 per cent when mechanical tools are used. In extremely high weed populations it was only reduced by about 30 per cent.

In other trials they found just using herbicide alone, could leave as many as 25 herbicide resistant weeds per square metre. However with a combination of herbicides and mechanical weed seed control, resistant weed numbers could be reduced to about one plant per square metre.

Dealing with herbicide resistant weeds is an ongoing challenge, “but it is not the end of cropping, despite the widespread problem,” says Walsh.

Lee Hart is a field editor for Grainews in Calgary, Contact him at 403-592-1964 or by email at [email protected]

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.



Stories from our other publications