Organic producers eager for Canada thistle control

Canada thistle has long been a thorn in the side of organic growers, and the problem is getting pricklier.

“It’s a growing problem on my farm,” Jim Robbins, a producer from Delisle, Sask., said during a research session at the 2010 Organic Connections conference.

In an interview after the session, Robbins said he summerfallowed an 80 acre field infested with thistle two years ago and seeded the field to barley the following year.

The barley outcompeted the thistle, and he ended up with a “beautiful crop” that yielded 60 bushels per acre and went malt.

In 2010, he seeded the same field to peas and the thistle came back with a vengeance, spurred on by the excessively wet conditions.

“It was pretty close to a disaster,” he said.

“The Canada thistle came on strong. There are big chunks of (the field) that I didn’t put through the combine because I wasn’t going to put that fluff all over the countryside, so I baled it.”

Robbins knows of two ways to control the weed:

• planting an infected field to alfalfa

for at least four years;

• putting the land into summerfallow and tilling the soil at least every third week, which is something he is hesitant to do with his sandy clay loam soil.

“I can only push with tillage so far and then I’m going to be abusing the soil,” he said.

Robbins urged University of Saskatchewan organic weed researcher Steve Shirtliffe to do whatever he can to find a better way to manage thistles.

Shirtliffe said he wrestles with the weed every year in his research plots and asked farmers for their advice on how to deal with it.

Martin Meinert from southwestern Saskatchewan said he conducted on-farm research this year to test his hypothesis that the depth and method of tillage could make a difference in weed control.

He said his farm provided the perfect testing ground for the research.

“I’ve got a tremendous amount of Canada thistle.”

He showed a photograph during his presentation of a spot in one of his research plots where he failed to properly seed it to sweet clover.

The spot contained a patch of Canada thistle that was as tall and densely populated as the neighboring sweet clover crop.

Meinert’s one-year research project showed that cultivating at a nine-inch depth resulted in slower regrowth of Canada thistle than at a three-inch depth.

He also found that the cultivator provided better control than his Noble blade, although he said the wet weather probably had a lot to do with that finding.

A farmer from northeastern Saskatchewan agreed with Robbins that tilling summerfallow land more frequently is the key to thistle control, although he expressed similar reservations about overworking the soil.

Shirtliffe said tillage isn’t “the anti-Christ of agriculture” as long as green manure crops are plowed under, which incorporates a lot of biomass into the soil.

“You can go out there and do some tillage and it’s not like all your land is going to blow away at the first puff of wind that comes up,” he said.

“You can’t adopt a full no-till system. You have to have some tillage in there to get rid of your perennial weeds.”

However, he acknowledged it is a concern to many organic growers, which is why researchers are looking for ways to reduce the amount of tillage on organic farms.

They have experimented with a roller-crimper to terminate a green manure crop rather than plowing it under.

Shirtliffe said the implement killed the green manure crop, but preliminary results show crop yields the following year were reduced because the organic material lies on top of the field rather than being incorporated into the soil.

Ross Murray from Young, Sask., said he has tried mowing his sweet clover to eliminate one of the tillage passes, but he found weeds were far more abundant on the 10 acres he mowed compared to the land he cultivated.

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