Herbicide resistance | With few alternatives, Australian farmers crush or burn weed seeds
Herbicide resistant weeds affect 40 percent of cropland on the Prairies, according to rough estimates.
However, Canadian farmers are still able to combat the problem before it gets as bad as conditions in Australia, where virtually every weed is assumed to be herbicide resistant.
Michael Walsh of the Australian Herbicide Resistance Initiative focuses all his time on the battle against herbicide resistant weeds. He and four Australian farmers explained their tactics to Alberta farmers in Lethbridge Aug. 12.
“The reasons why we have herbicide resistance is because we’re using herbicides alone to treat large populations of weeds, and the genetics within those populations for herbicide resistance are already there prior to the use of herbicides,” said Walsh.
“So now we’re just selecting for resistant individuals. The way to stop that or intercept that process is just to drive down the population density and you’ll reduce the chances of getting resistant populations occurring.”
One way to reduce density is to battle weeds at harvest by capturing seeds and crushing or burning them.
Prairie farmers typically manage weeds post-harvest and in spring, but pitching a battle during harvest is another tool in the arsenal, said Agriculture Canada weed specialist Bob Blackshaw.
“It’s sort of another window of opportunity that we don’t do much of at that time of year,” he said.
“We might be trying to control weeds in October after harvest. We have our weed control before we seed. We have our in-crop weed control, different things we’re doing. But this is technology done right at the harvest.”
The technology includes burning chaff piles and windrows and destroying seeds through crushing.
Lance Turner, who farms 150 kilometres southeast of Perth in East Pingelly, has been continuously cropping his land since 1990, when he sold his sheep. He soon ran into difficulty with herbicide resistant weeds.
He rejected the idea of capturing all straw and chaff in a cart off the combine because it slowed harvest and was prone to equipment breakdown. The resulting piles of pulverized, dry material were difficult to burn efficiently.
Instead, he installed a short chute on the combine and an elevator into a chaff cart, to catch only the chaff portion of combine discharge.
The cart is emptied along a designated line in the field during harvest. When conditions are right for burning, a shallow break is plowed around the row of chaff piles and they are burned.
“It’s not a silver bullet … but it’s a pretty big linchpin in a whole system,” said Turner.
“It’s about using all the tools that we’ve got in the toolbox. We’ve used fire, we’ve used chaff carts, we’ve used different chemicals in different rotations.”
Weeds in his region are resistant to several herbicide groups.
“Now we’ve got nothing left in our cereals to use.”
Turner said the chaff piles burn in eight to 12 hours and the job is usually done at night when there are fewer “willy willys” or dust devils.
He and Walsh acknowledged Canadians’ aversion to burning.
“It’s the same aversion in Australia,” said Walsh.
“There’s issues with smoke. Nobody likes to have smoke lingering in the atmosphere for days and days. There’s also the risk of fires getting away that can be devastating.
“Australian growers … are not cavalier about their use of fire for weed control. They are very careful about it because they recognize the dangers and the problems associated with it, but they also recognize that it’s a valuable tool.”
Australian farmer Rod Messina employs burning in a different way for weed control. The Mullewa-area grower has been burning windrows since 1996 to control weeds.
He and his brother and father crop 30,000 acres in a dry area at the northern end of the Western Australia wheat belt.
“Our whole system is focused on weeds. Everything we do, what crops we grow, rotation, we’re focused purely on longevity, being there tomorrow for our kids and controlling weeds as opposed to growing the most profitable crops year in and year out,” Messina said.
Wheat is the primary crop, at about 7,000 acres per year. Lesser amounts of lupins, canola and chem-fallow make up their rotation.
The Messinas attached a simple chute to their combine that places chaff into windrows as they straight cut in a controlled-traffic system.
The windrows are later burned, leaving long, blackened strips in the field. The technique has drastically reduced their weed problems.
“It’s amazing how quick you can drive numbers down,” he said.
“It’s about a numbers game. You can’t get 100 percent of everything,” but it does reduce the farm’s reliance on herbicides.
Messina estimates 99 percent weed control on material that comes through the combine.
Fires have gotten out of control only twice in the farm’s nine years of windrow burning.
Annual rye grass, once liberally planted for sheep fodder, has become Australia’s worst herbicide resistant weed. Brome and wild radish, a broadleaf, are also major problems.
“Herbicides have been indispensable in allowing us to conserve residues and reduce the amount of cultivation, but it has come at a cost,” said Walsh.
In Canada, wild oats is the most important weed economically, and it has developed resistance in 50 to 60 percent of fields, said Blackshaw.
Fifty-nine herbicide resistant weeds have been identified in Canada and 11 of them are found in Alberta.