Three ways to manage tough weeds on organic farms

Producer Steve Snider manages weeds the mechanical way, using mow tilling (pictured), harrowing, and plowing to tackle tough weeds like Canada thistle. Photo: Supplied

Using green manure, increasing seeding rates, and incorporating mechanical weed control can help organic producers manage weeds on their operations

By Jennifer Blair
OrganicBiz staff

The biggest challenge on Steve Snider’s organic farm is weeds — and killing them properly isn’t a one-size-fits-all operation.

“The key to remember in organics is there’s no one answer,” said Snider, who has been growing organic grain on his farm near Edberg, Alta., for 30 years.

If you’re not going to use green manure, don’t even start organic farming. – Steve Snider

“It’s not like conventional agriculture. You can’t control weeds with a herbicide. It doesn’t work that way. It’s a whole strategy that has a lot of tiers that have to build together and intertwine to work properly.”

And the first step for weed management on any organic operation should be green manure, Snider said at the Organic Alberta conference last month.

“I believe in GM crops — green manure crops,” he joked. “It’s a cornerstone. If you’re not going to use green manure, don’t even start organic farming.”

Even though seeding a crop (usually a legume) and then plowing it under is all expense and no revenue, Snider said green manure crops are “the ones that make you money.” In addition to adding nitrogen, other nutrients, and organic matter to the soil, they also act as a ‘smother crop,’ outcompeting weeds for sunlight, nutrients, and water.

“It’s tough to quantify because you’re not making cash on the year you put it in, but it does make you money,” he said.

Steve Snider. Photo: Supplied

Snider incorporates green manure into his fields with a disc, and he has also started plowing his fields to manage tough weeds, particularly Canada thistle.

“I was ornery about plowing, but we had one field where we had such weed pressures that we couldn’t get a handle on it. We went in and deep plowed it, and it did an amazing job,” said Snider.

Mechanical weed control is “more an art than a science,” though.

“The problem with post-emergent mechanical tillage is that there’s so many variables at play,” said Snider, who does some pre-plant tillage with a spike-tooth cultivator in front of a rod weeder, which pulls weeds mechanically.

“You can go out and do a post-emergent harrowing operation and have tremendous results or horrible results. If you’re under moisture stress, you can actually do more damage than good.”

Combining different types of mechanical weed control at different times in the growing season may yield the best results, researcher Lena Syrovy told conference attendees. She recommended either using a rotary hoe or harrowing early in the season and then doing some inter-row cultivation later in the season.

“The advantage of looking at these three different types of implements is that we have different windows where we can inflict management depending on the weed situation and the environmental situation,” said Syrovy, a research assistant in the weed ecology program at the University of Saskatchewan.

“Combining an early tool like a rotary hoe or harrow with inter-row cultivation gives really quite good weed control.”

But two passes with a machine is best, she added.

“You’d think that going in with all three tools would be the best thing, but that’s not always the case. You begin to see crop damage the more passes you go over the field.”

Syrovy recommends bumping up the seeding rate when using any type of mechanical weed control.

“The first reason is that increasing seeding rates makes crops a bit more competitive, but the other reason is that rotary hoeing and harrowing can sometimes thin the crop, so it helps to buffer against any kind of injury from your passes with your implement,” she said.

She recommends seeding at one-and-a-half times the recommended rate.

“In general, we’ve seen that raising the seeding rate is one of the most effective ways that you can consistently suppress weeds,” she said.

“Usually, we see a modest yield increase of about 10 to 15 per cent, but you really see benefits in weed biomass suppression. You’ll see around a 30 per cent weed mass decrease up to 50 per cent weed suppression just by increasing the seeding rate.”

And when all else fails, Snider turns to hay on his farm.

“If everything goes haywire on you and you can’t get a handle on thistle, we default into hay,” he said. “You mow those thistles, and they’re gone. Two cuttings on hay typically takes your thistle populations down quite nicely.

“Hay can be a fickle market — it’s up and down — but we’ve had tremendous success with it.”