The University of Saskatchewan has researched dandelion control for most of this decade.
Ken Sapsford, a research assistant with the plant sciences department, has been looking at the timing of spring applications: before flower; full flower or after seed set; fall versus spring applications and late September versus late October applications.
Research is also focused on a systems approach.
“We’re looking at all sorts of intensities, with all combinations, because a one shot control is not going to work on a perennial plant,” Sapsford said.
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In the warm spring that occurred in Saskatoon in 2003, Sapsford said a half litre glyphosate rate provided good control at pre-flowering and flowering but the effectiveness decreased when applications were made after seed set.
In 2004, with a cool spring, the pre-flowering application provided little control with the half litre glyphosate rate.
“With all the products we used, we saw a lot more consistency with the flowering stage than we did with the others,” he said.
“With one litre of glyphosate (in 2004), there was good control with the pre-flowering and flowering stage, while the post flowering drops off a bit, but not nearly as bad as a half litre.
“We see similar results with the PrePass. It looks a bit better than the glyphosate, but it took time to come through in 2004. It was a great treatment in 2003.”
Express, mixed with half a litre of glyphosate, had similar results as the other products.
“Because dandelion was the only weed we had, when we look at the yields, they reflect the kind of control we got on the dandelions,” said Sapsford.
“In 2003, where the pre-flowering gave us the best control, you can see that in the yields. There was a significant yield increase if we went in and controlled those dandelions early in the spring.
“In 2004, where the early application didn’t control well, we had better control on the dandelions at the flowering stage, but the yield was still better with the early control application. It was a dry year, the dandelions had sucked up a lot of moisture and they didn’t allow the crop to get control.”
He said early weed removal provides the best yields.
Sapsford said a fall herbicide application achieved 90 percent control of dandelions compared to untreated checks when rating control started May 11. The spring application would have gone on about that time but wouldn’t have controlled weeds yet.
Sapsford also compared a late September application to a late October application.
“A lot of farmers were saying, ‘If I’m going out in the fall, I want to wait until my winter annuals are up, so let’s go into a late October operation, where I can control my winter annuals and also take the dandelions.’ What we found is there’s a definite difference between a September and October application,” he said.
“We were looking at applications in the last week of September and the last week of October. With the one litre per acre rate of glyphosate, both were giving control of dandelions, but by June, the October treatment dropped off. There were new plants starting to come up.
“What I think is happening with the October treatment is we’re not getting the translocation far enough into the crown. We’re killing it off somewhat, but it’s able to put up leaves later on in the season.”
Sapsford looked at straight Express, which is an unregistered use because its label use is either mixed with glyphosate or Express Pack 2,4-D.
“In the research, we put straight Express on with a surfactant. With the September application, we had excellent control all through the season the next year. In October, we never did get up to the 80 percent control,” he said.
“We looked at Express Pack and the 2,4-D did not add anything to it compared to the straight Express. That’s one of the most economical treatments I’ve seen. You don’t need the glyphosate in there to add anything to it.”
When he started this trial, PrePass was not registered yet, so he used Spectrum as the florasulam product.
Sapsford said long-term control of dandelions will not be achieved with a one time treatment. Instead, he advised producers to take a systems approach.
