Most farmers’ ears perk up when Canada thistle is mentioned.
Even those who have had a lot of success at thistle control find it harder to keep the weed down when they reduce tillage or face a wet year.
Organic farmers learned about managing Canada thistle last month during a conference hosted by the Organic Crop Improvement Association Research and Education. Nearly every producer who attended the session had a Canada thistle story to tell.
The traditional recommendation has been to till the plants when they first start to flower. The plants are at their most vulnerable, with most of their reserves going into flowers and seeds.
The plants regrow after tillage, using up reserves stored in the roots. They are then tilled each time new sprouts come up, usually every two to four weeks.
They drain down their reserves each time they regrow, hopefully until they are depleted.
Several farmers have had success with this method of carbohydrate starvation.
The most common method is to cultivate to loosen the soil, followed by rod weeding. The rod can pull long sections of root out of loosened soil.
James Schiller of Regina said he could get up to nine inches of thistle root with his rod weeder.
Harvey Buhr of Raymore, Sask., said that thistle control took two tillage treatments and five passes with the rod weeder in a fallow year.
“You need a good average year” to allow that much tillage, he said.
Al Boyko of Canora, Sask., found that tillage from late August until frost was most effective. He lets the plants get no more than three inches tall between tillage treatments.
Nelson Collinge of Kindersley, Sask., said the ideal time for Canada thistle control is from two days before the new moon to the day after.
Brother Basil of St. Peter’s Abbey near Muenster, Sask., said cultivation was most effective under the new moon in September.
Buhr said tillage was especially effective in November, while others suggested it is most effective just before the ground freezes, before the snow comes.
However, using tillage to starve thistles concerns many organic farmers. The amount of tillage needed for thistle control can make the soil vulnerable to erosion. Many organic farmers are reducing tillage and modifying their thistle control strategies.
Paul Gaucher of Coderre, Sask., found that “when we started continuous cropping, the thistles really took off, especially in a wet year.”
Martin Meinert of Swift Current, Sask., said Canada thistles increased when he reduced tillage.
“I tried to do minimum tillage, and I can do it and be organic, but I came to the conclusion that I have to till more.”
He plans to use a Noble blade to undercut the thistles while still leaving trash on the surface to reduce erosion. Brother Basil said the abbey has tried mowing and baling, with some success.
Brent Hume of Carlyle, Sask., said he hopes that seeding early will allow him to swath the crop when the thistles are coming into flower.
Swathing thistles over a lentil crop has been successful at St Peter’s Abbey.
Meinert said he was able to successfully mow thistles in the first year of a biennial caraway crop.
Ken Stuhl of Hudson Bay, Sask., said Canada thistle can be killed if water gets down its hollow stem. He suggested swathing the plants in or before a rainfall.
Some producers find that strong crop competition sets back the thistles. Hume said sweet clover is a good competitor against thistle.
Collinge, Stuhl and Boyko had excellent results with three to five years of alfalfa cropping.
Del Affleck of Beechy, Sask., seeded fall rye on land that had a thistle patch starting.
“We’ve never seen Canada thistle since.”
Some farmers are looking at biological control.
“We tried digging and vinegar and tillage and mowing. They didn’t work,” said Tim Randles of Grenfell, Sask. “But our Dexter cows will eat the thistle heads.”
Brother Basil said painted lady butterflies provided the most effective control. Butterfly kits are available online and many producers were interested.
There was less interest in Collinge’s observation that three years of grasshoppers also controlled thistles.
Hume pointed out that controlling Canada thistle is an ongoing struggle. A variety of techniques are available and it is up to producers to determine what suits the land, the management and the weather.
Brenda Frick, Ph. D., P. Ag. is an extension agrologist and researcher in organic agriculture. She welcomes your comments at 306-260-0663 or e-mail email@example.com.