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Controlling seeds post-harvest

Can pulverizing weed seeds after harvest control weeds in Western Canada?

As buzz builds about Australia’s Harrington Seed Destructor, researchers are looking at whether pulverizing seeds after harvest will work on the Prairies. But preliminary research shows post-harvest seed control is unlikely to work for all of Western Canada’s weeds.

Breanne Tidemann presented new research at the Herbicide Resistance Summit in Saskatoon this March. Tidemann, who is completing a Ph.D. at the University of Alberta, looked at whether cleavers, wild oats, and volunteer canola seeds could be managed post-harvest in wheat and faba bean crops. The trials ran in 2014 and 2015 at sites near Lacombe, St. Albert, and Scott.

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Tidemann said there are two requirements for controlling seeds post-harvest. The first is the height the weeds are producing the seeds.

“If they’re producing them any lower than about 15 cm, we risk damaging our equipment too much to actually target them that low in the canopy.”

All three weeds passed that test. But the weeds also needed to retain seeds long enough for farmers to collect them. Researchers placed shatter trays under the weeds. They then noted how many seeds the weeds had retained at wheat swathing, wheat harvest, and faba bean harvest.

Volunteer canola is the best candidate for harvest weed seed control, Tidemann said. “It retains its seeds really well and it produces them high in the canopy.”

In fact, canola retained its seeds at all three sites in both 2014 and 2015.

The good thing about wild oats was they were also very consistent, Tidemann said.

“The bad thing about wild oats is that they’re consistently losing a large number of seeds very early on, to the point that the number of seeds that we could collect is not really going to impact the population,” said Tidemann. “So they are not a good target for harvest weed seed control.”

Cleaver seed retention varied between sites and years. For example, cleavers retained 80 to 90 per cent of their seeds until wheat swathing at Scott both years. In Lacombe, cleavers retained most of their seeds until wheat swathing in 2014, but seed retention dropped the next year.

St. Albert saw huge variability in cleaver seed retention. The first year cleavers had retained 90 per cent of their seeds by wheat swathing and 40 per cent at wheat harvest. But in 2015, cleaver seed retention was down to 50 per cent at wheat swathing, and nil by wheat harvest.

“This is the only location and the only year that we saw this in. Again, whether that’s because of low moisture or something else playing a role, we’re not really sure. And we still have some work to do to figure that out,” said Tidemann.

Cleavers still seem like a good target for post-harvest weed seed control, Tidemann said. But farmers might have to swath to catch seeds before they’re dropped.

Future research

Tidemann and her colleagues aren’t surrendering to wild oats yet.

One new idea is to target wild oats during seed formation. Researchers are looking at cutting panicles when they pop above crop canopies. Tidemann said after cutting panicles every week, they keep seeds to see whether they’re viable. Researchers are also leaving wild oat seeds on the ground to see how that affects wild oat populations.

Tidemann noted that cutting panicles with garden shears isn’t a great option for farmers. But farmers could silage crops. In fact, work done by Dr. Neil Harker shows that cutting barley for silage reduces wild oat populations, she noted.

Another weed-control option might be a CombCut, which Tidemann described as a selective mower with stationary knives. The idea is to run it through cereal crops at an early stage. Cereal plants will bend, avoiding damage.

“The broadleaves, they’re not going to bend. They’re going to get cut off.” It could also cut seed heads emerging above the crop’s canopy, she added.

Agriculture and Agri-Food Canada has also purchased a Harrington Seed Destructor to see how it handles weeds in Western Canadian crops.

“We have kochia. We’ve got wild buckwheat. How does that change how well the Seed Destructor can work? What about the number of seeds? If you have 10 seeds going through compared to a million seeds going through, how does that change it?”

Tidemann also urged farmers and agronomists to remember the basics when it comes to weed control. Good agronomy, such as higher seeding rates and the 4Rs of fertilizer application, go a long way to establish a competitive plant stand.

In over 90 research studies looking at 29 different crops, only six studies failed to show lower weed counts with higher crop density, she said.

“It’s a hard statistic to argue with.”

For a video interview with Breanne Tidemann, click here.

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.

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