Zap troublesome weeds in the fall

Whether it works best pre- or post-harvest depends on several factors

To hit up problem weeds, such as herbicide-resistant kochia (far left photo), Alberta farmer Dallas Vert applies a post-harvest weed control treatment of Valtera. Last year, Saskatchewan farmer Dallas Leduc’s post-harvest application of Roundup ProActive 360 tank mixed with four ounces of 2,4-D worked well on Canada thistle (middle photo) and narrow-leaved hawk’s beard (right) on his farm.

A sampling of western Canadian producers, when asked about their fall weed control measures, have most generally agreed that either a pre- or post-harvest herbicide application is a valuable management tool. Most of the farmers contacted leaned toward a post-harvest treatment with a glyphosate product, although there are a number of caveats that come into play.

Weather conditions that can drastically affect the timing of harvest and, to some extent, concern about marketing crops treated with glyphosate just before harvest are two of the leading factors that have farmers favouring post-harvest treatment.

But all farmers say nothing is written in stone. A lot of times, how they handle weeds in the fall, if there are any, depends on the crop, the weeds, the fall workload and certainly the weather.

Varied approaches

Josh Fankhauser. photo: Supplied

Josh Fankhauser
Southwest Alberta

In southwestern Alberta, Josh Fankhauser, who is part of a family-run mixed farming operation near Claresholm, northwest of Lethbridge, expressed a strong commitment to tackling weeds in the fall.

As he looks at the overall weed control program for his family’s grain and oilseed farm, he considers the most important treatment of the year is the fall-applied glyphosate that goes on post-harvest. “If someone said I could only do one herbicide treatment in a year, it would be the fall-applied glyphosate,” says Fankhauser. “It is the best time to control some of your most troublesome weeds.”

Craig Lehr. photo: Supplied

Craig Lehr
Southeast Alberta

By contrast, in southeastern Alberta, Craig Lehr, who is also part of a family-run mixed farming operation near Medicine Hat, says he seldom has to worry about either a pre-harvest or post-harvest herbicide application.

“We have been direct seeding this farm for about 35 years and we have weeds, but I wouldn’t say they are a particular problem,” says Lehr of Short Grass Ranches. It is a third-generation operation that includes an 1,100-head cow-calf operation, a 7,000-head backgrounding feedlot, dryland farming and about 1,000 acres of irrigated crop production.

He says farming in a drier part of Alberta means there usually is little weed regrowth after the dryland acres have been combined. And on the irrigated land they have developed a double cropping system.

Lehr produces several forages for silage under irrigation, including barley silage, a combination wheat and pea silage, corn silage and some triticale silage.

“As soon as those silage crops are harvested, then we spread manure on those acres before seeding a cover crop,” says Lehr. The cover crop is a forage mixture of winter wheat or triticale and forage radishes along with some brassicas.

When cows come home in the fall, they are turned out on the cover crop mixture to graze. Lehr doesn’t use any cross fencing and allows the cattle to graze the entire area.

“And we don’t seed the winter cereals and cover crop for survivability,” he says. “We want the cattle to make use of it. If the crop does survive over the winter that’s really a bonus. In the spring, if it looks like the winter wheat has survived, we will fertilize and then harvest it as a silage later in the summer.”

Lehr says with little regrowth on dryland acres and the cover crop program on irrigated cropland, weeds just aren’t an issue.

Dallas Vert. photo: Supplied

Dallas Vert
East-Central Alberta

In east-central Alberta, Dallas Vert says while a lot depends on fall growing and harvest conditions, he usually applies a post-harvest weed control treatment to grain and oilseed acres. Vert, along with his wife, Natasha, crop about 11,000 acres of grain, oilseed and pulse crops near Kirriemuir, Alta., just west of Altario, which is on the Alberta-Saskatchewan border.

“We usually try to cover most of the wheat and canola acres with a glyphosate product to control problem weeds such as dandelion and narrow-leaved hawk’s beard,” says Vert. “And we have also been using more Valtera (from Nufarm), which is quite effective on herbicide-resistant kochia.”

Vert does apply a pre-harvest desiccant on pea acres to help that crop dry down and ripen more evenly.

Due to dry conditions in eastern Alberta, Vert was done seeding by May 4 this year, about 10 days earlier than usual. That could mean an early harvest in 2021, and if it does rain, there is potential for uneven germination, and uneven crop maturity could “make for a creative harvest,” he says.

Vert has applied pre-harvest desiccant to all acres in past years if crops are particularly uneven, but for a weed control program he prefers the post-harvest period.

“It can vary, but usually we are done combining by mid-September, then we wait a couple of weeks for weeds to get growing and then apply the herbicide,” says Vert.

Terry James. photo: Supplied

Terry James
North-Central Alberta

A bit farther north, near Vegreville in north-central Alberta, Terry James says a fall herbicide treatment can be beneficial but a regular pre- or post-harvest treatment just hasn’t worked out on his grain and oilseed farm.

James says he believes a pre-harvest herbicide application is most effective to control problem weeds such as Canada thistle and quackgrass. By applying a pre-seed burndown, followed by in-crop applications of glyphosate on crops such as Roundup Ready canola, “really, quackgrass is no longer the problem it used to be,” says James.

Canada thistle can still be a concern, he says, but it hasn’t worked out to apply a pre-harvest herbicide application. And in recent years, the weather hasn’t co-operated to allow for a post-harvest treatment. “With wet and snowy conditions during harvest in recent years, there just wasn’t time for a post-harvest herbicide,” he says.

Pay attention to herbicide limits

Kris Mayerle. photo: Supplied

Kris Mayerle
Northeast Saskatchewan

In northeast Saskatchewan, Kris Mayerle at KRM Farms says depending on the circumstances, he will go with either a pre-harvest or post-harvest herbicide treatment on different crops.

“I will use a pre-harvest glyphosate treatment on any crops that I can,” says Mayerle, who crops about 21,000 acres near Tisdale. Because the farm also includes a pedigreed seed business, Greenleaf Seeds Ltd., he won’t apply a pre-harvest glyphosate to any of the seed crops, as the herbicide can negatively affect seed germination. “But if we have commercial wheat, oats or canola that I’m planning to straight cut, I will use a pre-harvest on those crops,” he says.

While a pre-harvest glyphosate treatment provides effective weed control against Canada thistle and other weeds, under certain environmental conditions it can help crops to dry down for more even maturity when combining. However, because glyphosate is not a desiccant, when used at pre-harvest timing weed control should still be its main objective. Mayerle says he uses a desiccant such as Reglone on pea and fababean pulse crops.

If a pre-harvest treatment isn’t possible, Mayerle will apply a post-harvest treatment that usually includes glyphosate tank mixed with 2,4-D “or some other product just to bump it up,” he says.

Mayerle says he doesn’t necessarily target treating all or even 50 per cent of his acres with a pre- or post-harvest application. “A lot of it just depends on the year, what crop it is, how much rain we got, how much regrowth we get after harvest and other factors,” he says. “Most years we always get part of the farm done.”

Dallas Leduc. photo: Supplied

Dallas Leduc
Southern Saskatchewan

In southern Saskatchewan, Dallas Leduc, who crops about 9,400 acres of grains, oilseeds and pulse crops near Glentworth, about 170 kilometres south of Swift Current, says he aims to apply a post-harvest herbicide application to most of the farm each year.

“We try to cover almost everything as long as conditions are favourable,” says Leduc. “I’ll use different products, but last year I applied one litre of Roundup ProActive 360 tank mixed with four ounces of 2,4-D per acre.”

The post-harvest treatment is quite effective in controlling problematic weeds such as Canada thistle and narrow-leaved hawk’s beard. “There were actually a couple of fields I didn’t get sprayed in the fall,” Leduc says. “Those fields didn’t have any particular weed problems, but when we came along in the spring I could see those fields certainly weren’t as clean as fields we had treated, so I could definitely see a difference.”

As Leduc produces durum, yellow peas, large green lentils, yellow mustard and canola, he is reluctant to apply a pre-harvest herbicide as it could affect crop marketing.

“More customers now really aren’t interested in buying crops that have been treated with glyphosate,” he says. “I grow peas that I sell into a glyphosate-free market, and I’m afraid if I used it as a pre-harvest on durum, I could get hit with a discount or the crop could be rejected. I have a fear that could happen some day, so I just don’t do it.

“And I like the post-harvest treatment because it gives me a bit more leeway to hit those weeds a bit harder than I would if it was pre-harvest,” says Leduc.

“I don’t think anyone would be interested in a large green lentil crop that had been sprayed with 2,4-D, for example,” he says with a laugh. “It wouldn’t be a good thing. But with a post-harvest treatment, I can use different tank mixes.”

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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