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Wild buckwheat: A weed to watch

Glyphosate alone is just not enough. Why is buckwheat so hard to control?

Wild buckwheat consistently ranks among the top five problematic weeds in Saskatchewan weed surveys. Clark Brenzil, provincial weed control specialist at Saskatchewan’s Ministry of Agriculture, explains what makes this weed so tricky.

Wild buckwheat is an annual weed found in cropland in the southern Prairies. Despite farmers’ best efforts, the weed is hardy and persistent to the point of infuriation. Each plant can produce up to 12,000 seeds in a single growing season. While they won’t all germinate, most of them will remain dormant in the soil, sometimes for years.

What makes wild buckwheat so hard to control? Part of the problem is that the weed blooms indeterminately throughout the growing season. It’s a vine-like plant that creeps along the ground before becoming entangled with the crop. Brenzil says that, ideally, wild buckwheat should be controlled at the four-leaf stage or smaller. Weeds that come later in the life cycle of the crop are less competitive, so producers will want to deal with the weeds that are there as the crop is coming up out of the ground.

“Once it starts putting on any amount of stem, then it has more lateral buds that can survive and re-boot the plant allowing the weed to continue growing,” said Brenzil.

Herbicides

Research shows that bromoxynil, clopyralid, dicamba, glufosinate and sulfonylurea products are the most effective wild buckwheat control. Bromoxynil has been one of the stalwarts for managing wild buckwheat in cereals, said Brenzil.

“It’s a contact, so its job is to burn the early leaves off, starving the plant,” he said. “But what that means is that you have to get wild buckwheat relatively early in its life cycle to get successful control.”

Systemic herbicides such as glyphosate and Group 2 herbicides have some challenges controlling wild buckwheat on their own.
photo: Supplied

Systemic herbicides such as glyphosate and Group 2 herbicides have some challenges controlling wild buckwheat on their own. If conditions are perfect they do a reasonable job, but if things are a bit cool or light is low, they will hold the wild buckwheat down for a while, but it ends up recovering and growing back later on.

Relative to other weed species, wild buckwheat has a low predisposition for developing herbicide resistance. In fact, there are only four reports worldwide. Group 2 herbicide-resistant wild buckwheat was confirmed in Alberta in 2007, but no cases of resistance have been reported in Saskatchewan or Manitoba. The Alberta sample was tested and found to be resistant to florasulam (a component of Frontline and PrePass), thifensulfuron (a component of Refine) and tribenuron (a component of Express and Refine). According to the International Survey of Herbicide-Resistant Weeds, one other case of Group 2 resistance was found in Australia in 1993, and two cases of resistance to atrazine (Group 5) were found in corn in Austria and Germany in the 1980s.

Another factor that makes wild buckwheat a challenge is the way its seed is designed. It has a relatively impermeable seed coat, which means the seed coat needs to be damaged from weathering to allow the seed to germinate. “And that never happens at exactly the same time in every seed,” Brenzil said. “So that means that you could have an extended germination of that weed out over a long period of time, especially if it got worked into the soil where it’s protected from those breakdown processes. This makes it hard to time herbicide applications just right.”

When wild buckwheat escapes

Because it’s a twining weed that climbs up the standing crop to reach sunlight, wild buckwheat creates mechanical entanglement problems during harvest. “It causes an increase in blood pressure, is what it does,” said Brenzil. “Because it slows down harvest. If you don’t stop to unwrap it from the header reel, it can cause damage to the bearings in the machinery.”

Wild buckwheat’s seeds can also act as dockage. For the most part, it’s relatively easy to clean out using screens, but if it’s not cleaned out well at the combine level it may have to be cleaned out at the seed cleaning plant level. It does count as dockage against crops with similar seed sizes, like canola, cereal and flax.

About the author

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Melanie Epp is a freelance farm writer.

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