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A bad year for crops has been a good one for weeds

Dry conditions have allowed weeds — including 
herbicide-resistant ones — to thrive in many fields

Reading Time: 3 minutes

Although dry conditions made weed control a challenge during the 2015 growing season, late-summer moisture and an early harvest may give farmers a decent chance to control perennial weeds.

“I’ve heard it said that 80 to 90 per cent of successful weed elimination comes from a competitive crop,” said Matt Gosling, an agronomist in the Strathmore area. “This year we didn’t have a lot of competitive crops and I saw a lot of dirtier-than-normal fields.”

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Canada thistle thrived in the dry weeks of May and June and winter annuals were also prevalent in fields across the province.

Pre-harvest glyphosate applications are favoured by many farmers for its two-for-one desiccation and weed control benefits, but it may not be the best way to control stubborn weeds this year.

“In most circumstances, we have good staging for spraying weeds now, but it makes me nervous that we have so many days before weeds go into dormancy,” said Gosling.

This year, applying herbicide after harvest may be the better option as it gives perennial and winter annual weeds less time to grow through the chemical application and survive the winter. A post-harvest application also offers more flexibility for tank mixing various herbicides with the glyphosate — an industry-recommended strategy for reducing herbicide-resistant weeds.

His customers have plenty of time to control weeds after harvest, said Gosling.

“We’re already into harvest a month earlier than normal so we’ve got maybe 50 days before long-term frost patterns set in. The most successful perennial weed control I’ve seen is in early October.”

An early harvest also gives farmers another weed control option that does not increase selection pressure for herbicide-resistant weeds such as wild oats. Winter cereals — while a “logistically challenging crop to get in” — provides the early-spring competition necessary to keep many weeds in check.

“Every time I’ve ever grown winter wheat, I can’t remember spraying for wild oats,” said Gosling. “Every time we don’t spray we buy ourselves one more year of resistance.”

Gosling actually recommended not spraying for wild oats in some of his clients’ spring-seeded crops this year. Where dry spring conditions made for tight budgets and very low wild oat presence, Gosling thought it was worth cutting out a year of herbicide tolerance selection pressure, even if it meant a few wild oats went to seed.

Wheatland County farmer Jay Schultz feels he isn’t sure whether skipping a spray is the right choice. He understands the principle behind decreasing selection pressure, but his goal is to “overall decrease (the) number of weeds for the long term.”

Schultz faces a challenge in a field of peas where lab tests confirmed Group 1- and Group 2-resistant wild oats this year. He sprayed the crop with glyphosate before harvest and since the wild oats were still green, he hopes the chemical they take up will reduce the vigour of the seed. After harvest he plans to pull out a heavy harrow with Valmar to spread granular wild oat herbicides like Treflan and Avadex which are from herbicide Groups 3 and 8.

Unlike the clichéd advice, “If it’s not broke don’t fix it,” Schultz’s mantra on herbicides is, “If something works, change it.”

He has read about farmers in Australia and the United Kingdom who are spending more than $100 per acre to control various herbicide-resistant weeds.

Along with diverse herbicides, Schultz hopes to mix up his crop rotation. He’s considering planting winter wheat in a couple of years and after that may look at various forage crops that local livestock owners could cut for feed or graze cattle on.

It takes extra planning and logistics to make this multi-pronged weed control strategy work, but for Schultz it’s worth it.

“We don’t want to abuse what we have.”

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