Pulse School: Knowing herbicide history and tackling weeds early on

(Kara Oosterhuis/RealAgriculture)

Depending on where you farm across the Prairies, you might have some concerns about herbicide carryover from the previous year, especially after a dry fall.

“If you’re in some of the drier areas of the prairies, especially southern Alberta or across Saskatchewan, you might want to take a look at some of the herbicides you used last year and not necessarily assume they’re gone,” says Robyne Bowness Davidson, pulse research scientist at Lakeland College.

There are a number of factors that play into herbicide carryover — moisture being one of the most important, as water can break down chemical molecules into less active pieces.

Which leads to the next factor, which is soil texture. Soils with high organic matter or higher clay content have a better chance at binding chemical molecules to their clay particles. Because of that organic matter content, they’ll also have more soil microbes, which are also responsible for breaking down herbicides.

It’s important to note that herbicide carryover can build up from more than one year, so having that herbicide history recorded is really important.

“The ones that come to mind the most would be group 2s — your group 4s and maybe some of your group 27s seem to be the ones that affect the pulses repeatedly every year,” says Bowness Davidson.

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If you’ve determined that there isn’t a chance of herbicide carryover in your target fields, the next concern is keeping your pulse crop free of weeds — especially during the critical weed-free period.

Bowness Davidson says that it doesn’t matter which pulse crop you’re talking about, none of them are good competitors with weeds and right now is the time to be thinking about weed issues in the field from last year, or when a pulse was grown in that field.

In a minimum till or zero-till operation there are pre-seed burn-down products that can be safely used. But, Bowness Davidson cautions that using a pre-seed burn-down product needs to be pre-seed, not pre-emergence.

The critical weed-free period to protect the crop against competition, and yield loss, is the window from when a pulse crop emerges up to the faster vegetative growing stage — the first four to six weeks, says Bowness Davidson.

Keeping those fields clean, and being mindful of herbicide history will set your pulse crop up for success.

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