LETHBRIDGE – The spread of direct seeding and the corresponding reduction in tillage has resulted in near epidemic outbreaks of foxtail barley in parts of Western Canada.
Bob Blackshaw, a weed researcher at Agriculture Canada’s Lethbridge Research Centre, told farmers at the recent Agronomy Update conference in Lethbridge that tillage controls foxtail under conventional cropping systems. One of the few prairie weeds native to the region, it grows well on all soil types, including saline soil.
“It’s a perennial bunch grass, with a reasonably shallow, fibrous root system, but has no rhizome system like quackgrass. Because of that, it’s well controlled with tillage, but as we’ve moved to zero till, we’ve had more of a problem with it,” Blackshaw said.
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“Foxtail barley is a big seed producer: thousands of seeds per plant. They’re small seeds with big awns, they don’t weigh a lot and are easily moved in the wind.”
The seeds primarily germinate in cool moist soil in September, October, April and May. Because light enhances seed germination, seed sitting on the soil surface in a zero till system finds ideal conditions.
“It’s a small seed, so if you bury it, it doesn’t have enough seed reserves to make it to the soil surface. It likes to germinate on the soil surface but down to two or three centimetres is also OK,” he said. “It’s not a hard seed coat, so it doesn’t persist in the soil like wild buckwheat or round-leaf mallow seed might. This one will only persist in the soil for two to four years, so if you can deplete the soil seed bank, you can get on top of this.”
Blackshaw said plants can resume growing in the spring, at 3 to 5 C.
“In southern Alberta, that may be March, so they can get a head start on a lot of species.”
Glyphosate is the key herbicide to control foxtail barley.
“I would recommend you go with a half to three-quarter litre per acre rate in spring as your pre-seed burndown. I’d go with a higher rate in the fall.
“The lower rate will control the small seedlings that germinated in the fall or early spring, then give some suppression of the larger plants and protect your yield. But you’re not going to kill the big foxtail barley plants when you spray glyphosate in the spring. You’re not getting translocation down into the root system.
“In the fall, go with a higher rate to target those big plants. Our best scenario is when we have a half litre rate in the spring, combined with a one litre rate (in the fall).”
Blackshaw said in the fall producers have pre-harvest and post-harvest opportunities to control the weed.
“That pre-harvest treatment will not be as consistent as you might expect with quackgrass or Canada thistle. Foxtail barley matures pretty early in the season, like the first weeks of August. If you have senescing plants with brown leaves, they’re not going to take up the herbicide very well or translocate it to the root system,” he said.
“If the plants are green and actively growing, that’s good timing. If that’s not the case, a post-harvest treatment in the first week of October, following some rains, might allow the plants to regrow and allow better weed control.”
Effective in-crop herbicides are limited in wheat. Sundance provided excellent control, but its availability is disappearing. In canola, options include herbicide resistant varieties, while graminicides work in pulse crops and oilseeds.
“Foxtail barley is a relative of barley, so if there’s any herbicide that injures barley, it has a chance to injure foxtail barley. You might not get control, but you may get some kind of suppression. Achieve, safe on barley, so zippo control. Horizon, you can’t use on barley but we got a little bit happening. Puma, nothing,” he said.
“Sencor gave pretty good control on small seedlings, but it dropped off on larger seedling plants. On plants one or two years old, it would be almost zero. With the graminicides used on pulse crops and oilseeds, Assure, Poast and Select are all pretty good on small plants, but Assure shone on larger plants. Assure is the absolute best choice for downy brome and it’s exactly the same story for foxtail barley.”
Blackshaw said other options include higher seed rates, fertilizer placement and tillage.
“Many have switched to direct seeding and zero till, but I don’t think it’s heresy to talk tillage. We shouldn’t forget about the options out there and how we might use them,” he said.
“This is one weed species that’s exceptionally well controlled with tillage because it has that shallow, fibrous root system. You don’t have to turn the soil over or double disk it. You can go in, undercut it and be very effective.”
Tillage is better in fall than spring.
“If you have a situation that’s got out of control on you, I’ve had some producers go in, till, reset the clock and get the population under control. Then they could get into a better herbicide program or crop rotation to manage it,” he said.
“Maybe just around sloughs, on field margins or the worst spots in your field. It can be quite effective. Everybody worries about the advantages of zero till. You’re not going to lose them all with one shallow tillage operation like a Noble blade.”
Blackshaw stressed that foxtail barley control is a multi-year strategy.
“Even that glyphosate treatment, with one or 1.5 litres, we probably never got more than 75 or 80 percent control of those large clumps of foxtail barley. At the end of two years, you’d probably be up around that 95 percent control.”
