LETHBRIDGE – Research at the University of Saskatchewan suggests farmers should spray their fields for dandelions in the fall rather than the spring.
And they shouldn’t wait until October. September is best.
Ken Sapsford, a research assistant in the university’s plant sciences department, said Express, Express Pack, PrePass and Spectrum, which are all applied in September, provided the longest and most consistent control over a variety of dandelion control trials.
“If dandelions were not treated in the fall, then a spring application should be made as early as possible for maximum yield benefit,” Sapsford said.
Read Also
VIDEO: Green Lightning and Nytro Ag win sustainability innovation award
Nytro Ag Corp and Green Lightning recieved an innovation award at Ag in Motion 2025 for the Green Lightning Nitrogen Machine, which converts atmospheric nitrogen into a plant-usable form.
“It might not give the highest control of the dandelions, but do it for the yield benefit.”
When applied in spring, research results showed PrePass at its recommended rate worked better than glyphosate at a one litre rate. Glyphosate at one litre was similar to half a litre of glyphosate plus Express.
“When you’re dealing with perennial weeds you’re looking at different strategies than with annual weeds. If you can understand the biology of that weed, even if you don’t know what’s going to work on it for controlling it, you can say those are the points that we need to hit,” Sapsford said.
“With a dandelion, we’ve got a tap-rooted, long-lived perennial plant. It flowers in April and May, then again from August to October. That tells you that’s the time that plant is most actively growing. If we’re going to control this thing, those are the two times of the year we need to look at hitting it.”
Trying to control dandelions once the crop is up is not nearly as effective because the weed is more or less dormant through the summer.
Sapsford said dandelions are becoming a serious weed problem in direct seeding systems because dandelion seed germinates best in full light, on the soil surface.
“If you bury the seeds, they’re not going to germinate. Our direct seeding systems have created an environment for dandelions.”
Glyphosate will control dandelion plants up to six inches across at the one litre rate. With mature plants, the recommended rate goes up to two litres.
“I don’t know many people who put on two litres in the spring and I wouldn’t recommend that. There’s better options,” Sapsford said.
Herbicides such as Amitrol 240, PrePass and an Express plus glyphosate combination are registered, but Sapsford said many registrations are for seedlings and not for the larger dandelions.
“There are products registered for in-crop control, primarily in cereals, but none of those are full control. They’re either top growth, seedlings, spring rosettes – none control the large dandelions,” he said.
“With pre-harvest, glyphosate is registered at one litre per acre. But the best time is to go in with a post-harvest application. At pre-harvest, the dandelion is below the crop canopy. It’s tough to hit. And it’s not exposed to a lot of light at that time, so it’s not actively growing.
“Wait until you take that crop canopy off the top, get some fall rains, it actively starts growing and you’re much better off at that time.”
Dandelion seedlings are another problem with a pre-harvest application. Sapsford said they can germinate after the crop canopy disappears in the fall, so farmers can effectively control the weed pre-harvest, only to get a rain a month after harvest and have a blanket of dandelion seedlings crop up.
Sapsford said dandelions reproduce through wind-borne seeds as well as by root cuttings. If a root is cut off halfway up the crown, with good moisture conditions there could eventually be two plants where there used to be one.
“The crown will send down new roots and the root left stuck in the ground will send out a new shoot. If you’re going to control dandelion with tillage, you’re going to have to go in deep. You have to get below that crown, rip the crown right out of the ground,” he said.
“You’ll have to get in below four inches in order to rip those crowns, with a heavy duty cultivator or plowing. When you go in with a discer or shallow tillage, it’s not effective. You’ll end up cutting the crown off and end up with at least one, if not two plants where every one of them was before.”
