Controlling those dastardly dandelions

It is the year of the dandelion. The hardy perennial pests are bigger and more plentiful in fields across Ontario than farmers can ever remember.

University of Guelph weed scientist Peter Sikkema has been fielding many questions about why the weed is so abundant this spring and how best to control it. When it comes to the bountiful crop of dandelion, however, he admits he doesn’t have a good scientific explanation.

Many agronomists point to the 2022 crop year when a combination of dry conditions and expensive glyphosate led many growers to shy away from using high rates of the herbicide. With those reduced rates, and tap roots driving deeper in the dry soil profile, many plants avoided attempts at fall control and slipped through the cracks.

When it comes to control, Sikkema says dandelion management strategy doesn’t really change. Based on his research, “as dandelion get bigger you have to increase the rate of glyphosate to get commercially-acceptable control.”

When it comes to rates, Sikkema says a dandelion four inches in diameter can be controlled with .67 litres of glyphosate per acre; a six-inch plant requires 1 litre per acre; and plants that measure eight-inches will need 1.33 litres per acre.

For better control in reduced or n0-till, the best way to tackle dandelion is to increase the rate of glyphosate in the burndown, says Sikkema. The story is a little different in soybeans where Classic herbicide makes a “pretty nice tank mix partner with glyphosate for the control of dandelion,” he adds.

Of course, the best control happens in the fall, so keep that in mind for later this year.

One advantage that growers have this spring, notes Sikkema, is the relatively warm temperatures. “Glyphosate is a slow-acting herbicide at the best of times and it’s an even slower-acting herbicide when you have cool temperatures. It’s a far faster-acting herbicide as temperatures increase.”

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