Tight crop rotations in the hot seat

Rotations were a major point as discussions turned to blackleg during this year’s BASF Knowledge Harvest

Agronomist Peter Johnson doesn’t like Manitoba’s tight rotations.

It’s all but impossible to eliminate sclerotinia and blackleg from the field, but it’s also a mistake to assume crop genetics alone will manage the problem.

BASF technical service specialist Colleen Redlick said farmers need to broaden their approach during the BASF Knowledge Harvest in Brandon earlier this winter.

Resistance breakdown, something the industry has noted with alarm, was near the top of the agenda during the one-day event.

Mixing strategies

Redlick stressed crop scouting for disease management along with longer rotations, something echoed by RealAgriculture agronomist Peter Johnson, among other speakers of the day.

The message is nothing new to producers, with experts ranging from university researchers and government-hired specialists to commodity group staff giving similar advice.

Outside disease pressure, along with weed resistance and other pest management concerns, those same experts also point to yield. Planting a crop on top of itself will inevitably lead to a yield drag, they argue, while the right, diverse rotation can boost grain going into the bin.

MASC data has provided ammunition for those arguments.

Yield data from 2010-16 shows crops ranged from 79 to 93 per cent of expected yield if planted into the same crop’s stubble. Select crops can leapfrog expected yield if rotated in the right order, the same data showed. Wheat showed 107 per cent of expected yield if following soybeans and 102 per cent following field peas or sunflower; barley got a boost following canola, soybeans, peas, flax or sunflowers, and soybeans benefited from following a crop of spring wheat or grain corn.

The argument has not taken root with all farmers however, and the most common rotations remain tight as producers maximize acres of their most profitable crops.

“The challenge really is that everybody is driven by short-term economics,” Johnson said. “And they have to be, because if they don’t pay enough land rent, somebody will rent it away from them, so we get pushed into these short rotations because, if canola is the most profitable crop, then you grow too much canola. In Ontario, soybeans is the most profitable crop; you grow too many soybeans and it’s the age-old problem, or challenge, of short-term gain for long-term pain. I would argue that the disconnect here isn’t nearly as bad as it is in some other places because guys at least will recognize that they should rotate and will if they can economically afford to do it.”

Johnson set the minimum ideal rotation at three years, although organic crops may require more than double that time to help break disease cycles and lessen resistance pressure.

Rotating varieties may also lessen the strain with a single crop, Redlick added.

“A lot of growers get one that they really like on their farm and they want to continue to use that year after year. That’s just maybe not the best management strategy,” she said. “And then, of course, once you’ve identified that breakdown on your farm, that’s where that early fungicide application can help with your ROIs (returns on investment).”

New tools for blackleg

Blackleg has reclaimed its place as a top concern in recent years, with producers noting that the resistant varieties they’ve come to rely on are, in some cases, no longer making the grade.

According to data presented to the Western Committee for Plant Diseases (and repeated by Redlick), blackleg’s prevalence rates hit 63 per cent in Manitoba in 2017. At the same time, prevalence has generally risen since 2008 across the Prairies, notwithstanding a brief dip from 2012-13 and despite the use of resistant varieties.

BASF technical service specialist Colleen Redlick demonstrates varietal resistance. photo: Alexis Stockford

The problem has prompted an ongoing quest for solutions. AAFC Saskatoon, for example, has unveiled new genetic labelling tools, something it says will let them target the exact strain of blackleg present in canola fields and allow producers to better select their varieties. Head researchers promoted their project at industry events last summer.

Redlick said there’s potential in those emerging tests, but more hurdles to cross before farmers can fully take advantage.

“I think that’s great,” she said. “The more information, the better. I think we still have a few caution flags there. It’s great to know the strain in your field, but then you also have to match that with the matching genetics, so we’re not quite there from the seed side.”

About the author


Alexis Stockford

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.



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