Wet fall and late spring a recipe for increased weed risk

Pre-seed burn-off will depend on what’s popping up in your fields, so scout early, says weed scientist

You won’t hear weeds complaining about the weather — which adds up to another headache for producers.

“Because we were so dry last spring, there were quite a few fields that didn’t get a pre-seed burn-off because there was nothing growing yet. I don’t think that’s going to be the same circumstance this year,” federal research scientist Breanne Tidemann said April 23.

“We’ve got a fair bit of moisture, and it’s been a fairly late spring. We’ve switched from cold and snowy to warm and sunny with a fair bit of moisture, and weeds will jump at that.”

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Soil background

It’s not just that there will be more weeds, but also that they will have more of a head start on crops.

“Because those weed seeds are already in the soil seed bank, if they’ve got a lot of moisture from the snowmelt, they’ll take advantage of the heat and start growing, which gives them an advantage over your crop because your crop’s not seeded yet,” said Tidemann.

“If you don’t control those weeds, they’re going to have a big competitive advantage.”

The risk is higher in fields with late or unharvested crops.

“There’s some pretty good potential for heavier pressure from volunteers than we might normally see, and because we had a fairly wet and unpleasant fall for harvest, weeds that can emerge in the fall and overwinter might have increased pressure as well.”

But producers should treat every field as a separate case, scouting for both the dominant weed species that are present and how much they have advanced.

“It’s not necessarily going to be a huge issue as long as you do your scout and a good, effective pre-seed burn-off,” she said.

The best time to scout is once the fields are dry and weeds are starting to emerge.

“If you’re thinking about spraying in the next couple of weeks, it would be a good time to get out there and look at what’s coming up.”

Once you know what type of weeds are coming up, you can target your pre-seed burn-off more effectively. If the weeds aren’t killed before the crop begins to emerge, controlling them with an in-crop spray can be very challenging, she said.

“The more days ahead of your crop that the weed comes up, the much bigger competitive advantage it has,” said Tidemann. “A wild oat that comes up three days before your crop compared to one that emerges at the same time is way more competitive. It’s got a jump on the crop in terms of light, nutrients, and moisture.

“By the time you get to your in-crop spray, the plant is too big to really get an effective kill on.”

It will also be important to use multiple modes of action during the burn-off — especially in fields that already have herbicide-resistant weeds.

“Glyphosate is great, but we all know the pressures around it — the more you use it, the more the risk of resistance goes up,” said Tidemann. “So put something else in there with it. It’s really important to have those multiple effective modes of action.”

About the author

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Jennifer Blair

Jennifer Blair is a Red Deer-based reporter with a post-secondary education in professional writing and nearly 10 years of experience in corporate communications, policy development, and journalism. She's spent half of her career telling stories about an industry she loves for an audience she admires--the farmers who work every day to build a better agriculture industry in Alberta.

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