Burn, bale or smash to fight resistance

57 percent weed reduction | With herbicide resistant weeds on the rise, interest in mechanical weed seed removal grows

EDMONTON, Alta. — Herbicide resistant weeds were an issue for Australian farmers long before they became a serious problem for Canadian growers.

Michael Walsh, a professor and researcher with the University of Western Australia, has just completed more than 10 years of research into the value of mechanical weed seed removal in combination with herbicide control.

Resistant weeds such as rye grass and wild oats are significant problems for the Australian industry. Chemicals such as glyphosate are not as effective as they once were.

“Growers created this issue. The economics of farming in the 1990s and early 2000s meant that they were inclined to cut rates on their herbicides and overuse the least expensive (ones). The products did a pretty good job of managing the (weeds) at lower rates, but they also created ideal (natural) selection of the weeds,” he said.

“Combines got larger and more efficient and chaff and straw spreading got better. For weeds, that is compounding the problem of the farmers’ weed selection. Now they are seeding those weeds back into their fields, making spot control impossible.”

Ninety-eight percent of weeds in Western Australia are now herbicide resistant, often to multiple active ingredients.

The problem caused producers to turn away from vulnerable crops such as pulses and grow hardier canola, wheat and barley.

“That resulted in fewer rotational choices and more dependence on the herbicides that we are already having resistance issues with,” Walsh told a Farmtech session in Edmonton last week.

Farmers began removing weed seeds from the back ends of their combines about 30 years ago, when the first Redekop chaff wagons were exported to the country. They were reducing or eliminating tillage in favour of continuous cropping and water conservation.

“Chaff wagons worked for smaller farms and where they had livestock to use the chaff in a ration,” he said.

“The chaff piles could be grazed by stock or gathered up and fed in a feeder yard.”

The system uses a cross auger to collect chaff off the combine’s top sieve, and a blower puts 85 percent of the weed seeds into a cart.

However, the practice has declined as broad acre producers shed their livestock herds in favour of specialization and increasing farm sizes made hauling the feather-light chaff inefficient.

“Farmers saw the benefits of weed seed removal, but they had to adapt after the carts,” Walsh said.

Instead, they either collected the weed seeds with the chaff and burned the piles or used concentrators on their straw and chaff output to create tight windrows that were then burned.

Seventy percent of Western Australia’s 25 million farmed acres now use fire to deal with weed seeds.

A farmer in Western Australia im-proved on the blower design in the 1990s by adding a conveyor to carry the material back to the wagon, along with 25 percent of the straw.

Walsh said this results in a denser pack of chaff and more complete and rapid burning of the piles.

About 200 farms in the region still use some form of wagon system.

“The Shields family farms about (30,000 acres) at Wongon Hills, Western Australia, and they went one better with a large square baler design behind the combine,” he said.

The system draws about 80 horsepower in hydraulic flow back to run the baler, which bales the straw and chaff from the back of the combine. The machine’s $190,000 price tag makes it an expensive option.

The Shields sell their bales to a feed company that turns the crop byproduct into pellets, which are fed to sheep as they move by ship to the Middle East. The system captures 95 percent of the weed seeds that come through the combine.

“You need a market for the (straw) to make that alternative work,” said Walsh.

Most producers choose to condense the straw and chaff in a windrow and burn the result, despite the fire risks and the labour intensive process.

“The Messina family pioneered that process and these days it takes them about a month to burn their (30,000 acres) of windrows,” he said.

Ray Harrington, who sold his livestock in the mid-1990s and moved into grain production, wanted to avoid the already serious issue of herbicide resistance that other grain producers in his region were experiencing.

Harrington drove a cage mill with a set of belts from a 200 horsepower motor. The unit trailed behind his combine, smashing weed seeds in the chaff and then passing the material through a straw chopper and spreader.

He handed the project over to the University of Western Australia to further develop and commercialize. Further improvements were made using farmer grain check-off money matched by government research funding.

The machine is now available for sale, but the $260,000 price tag is probably why only four units have been sold. One of the machines went to Agriculture Canada for testing on the Prairies. It will be delivered in April.

The current incarnation of the cage mill is hydraulically driven and features a paired set of counter rotating pins in two cages, each with three rows of interlocking bars countering one another.

“It is very effective, over 90 percent,” Walsh said.

“Ninety-nine percent on wild oats.”

Whether farmers use the Harrington system or capture and burn their chaff and straw, Walsh said the results are the same: a 57 percent reduction in weed seeds.

“Might not seem like enough, but it works out,” he said.

Mechanical removal reduced weed populations to less than one per sq. metre over 10 years of trials when combined with herbicide strategies. It was significantly better than results from herbicides alone , which allows five to 10 weeds to survive, he said.

“Together, it deals with the problem of resistance selection pretty well.”

About the author



Stories from our other publications