Study examines harvested weed seed control

Volunteer canola was the best candidate because it retains its seeds high in the canopy, unlike wild oats which constantly shed

Harvested weed seed control is a strategy to prevent viable weed seeds from returning to the field at harvest.

It has proven useful in Australia in the fight against herbicide resistant weeds such as rigid ryegrass.

Breanne Tidemann, a Ph.D. student at the University of Alberta, is studying which prairie weeds are vulnerable to the strategy by examining if they meet two requirements: seed height and seed retention at harvest.

“If they are producing them any lower than 15 centimetres, then we risk damaging our equipment too much to actually target them that low,” Tidemann said during the recent Herbicide Resistant Summit in Saskatoon.

“The second thing is seed retention. If weeds have already dropped their seeds to ground when we go to harvest, we cannot control those weeds with post-harvest weed seed control.”

Tidemann has focused on wild oats, volunteer canola and cleavers to determine how they fit in terms of those two requirements.

Wheat and fababean trials, at regular and double seeding rates, cross-seeded weed seeds and then placed shatter trays under the weeds before seed loss to monitor when they seeded out.

“We harvest plants at three different timings — wheat swath timing, wheat harvest timing (straight combine) and fababean harvest timing (straight combine) — to see what is still on the plant at those times to get a percentage of the seed retained over time,” Tidemann said.

Volunteer canola was the best candidate for harvested weed seed control because it produces its seed high in the canopy and also retains its seed well.

Cleavers were more variable between test sites and years, possibly because of variations in heat, precipitation and competition from volunteer weed populations.

However, cleavers retained seed well until the time of wheat swathing, and then seed retention declined rapidly.

“In order to actually target them, we may have to include swathing into our harvest routine,” she said.

The study found that wild oats is not a good candidate for harvested weed seed control, even though it produces seed high in the canopy.

“The bad thing about wild oats is that they are consistently losing a large number of their seed very early on, to the point that the number of seeds we could collect is not really going to impact the population,” Tidemann said.

The harvested weed seed control strategy includes windrow burning and rotting, baling, chaff carts and the Harrington seed destructor, which processes weed seeds through an opposing cage mill.

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