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Destroying weeds – at harvest

The Harrington Seed Destructor is showing some potential as a way to manage weeds without chemicals – but will it work on Ontario weeds?

Combines and harvest practices in general are great weed seed distribution systems.

Think of all those weeds going in the front of the combine and then blowing out the back, all over the field. But what if you could destroy most of those weed seeds before they hit the ground?

Canadian research on an Australian innovation makes it look possible — at least with some weeds.

Breanne Tidemann, Agriculture and Agri-Food Canada research scientist based in Lacombe, Alta, has been studying how effectively the Harrington Seed Destructor chews up weed seeds. Tidemann and her colleagues collected chaff from a bag attached to the back of a combine. Then they ran the chaff and weed seeds through the seed destructor.

Researchers tested kochia, green foxtail, cleavers, volunteer canola, and wild oats in barley chaff. They also tested different volumes of chaff and seed, and seed sizes, in the Seed Destructor. Each treatment was repeated four times.

Statistically speaking, there were differences between how the Harrington Seed Destructor performed in each treatment. But those differences will make little difference to farmers in the field. The Harrington Seed Destructor destroyed 95 to 98 per cent of the seeds, no matter the seed type, size, number, or amount of chaff, Tidemann said.

“It just seemed to work.”

Tidemann and her colleagues are working in peas, canola, and wheat both swathed and straight cut.

Not every Canadian weed will be a perfect fit for the Harrington Seed Destructor. In fact, research to date suggests it will work best with the shorter season crops.

Tidemann outlined three conditions for harvest weed seed control to work:

  • Weed seeds must be on the plant at harvest time.
  • Weed seeds need to be at the right height so they can be collected by the combine.
  • The weed must be harvestable, and must go through the combine.

For example, kochia tends to tumble right over the header, meaning it might not be a good candidate for the seed destructor. And previous research by Tidemann and her colleagues found that wild oats often shatter before harvest, so harvest weed seed control alone won’t control all wild oats.

Researchers haven’t tested the Seed Destructor on weeds commonly found in eastern Canadian crops, such as Canada fleabane, red root pigweed and ragweed.

“The success of the seed destructor in the east would depend on seed retention of the weeds,” Tidemann told Farmtario.

Research into the seed-setting and shattering behaviour of fleabane, pigweed and common ragweed isn’t encouraging.

Research posters published by a team of AAFC researchers led by Marie Josée Simard in Saint-Jean-sur-Richelieu, QC, suggest it might have limited use in late season crops such as corn and soybeans because more than 70 per cent of weed seeds are shattered before harvest.

For fleabane, “control operations to limit dispersal at harvest would not be recommended as seed production peaks before harvest and the seeds are prone to shatter as soon as they are mature,” the researchers said.

The best time to control redroot pigweed in corn and soybeans is in late July before weed seed production and possibly early August for common ragweed.

“Destroying weed seeds harvested with the crop would not have been very useful in spring wheat as few weed seeds were mature,” the researchers said. “In corn and soybean, the percentage of seeds dispersed at harvest was lower than expected but an evaluation of the cost-benefits would be required as the weeds had dispersed hundreds of seeds.”

Both papers noted adding spring wheat into a corn and soybean rotation would be helpful in controlling the spread of weeds that have developed multiple herbicide resistance.

Practical lessons

Tidemann has learned a few practical lessons from her first harvest with the tow-behind Harrington Seed Destructor:

Air velocity is important. If there’s not enough air velocity, the equipment will plug.

Don’t harvest green or wet material. It doesn’t grind as well, and it tends to plug.

The tow-behind unit doesn’t handle hills well. The tubes attaching the combine to the Harrington Seed Destructor tend to accordion.

But farmers interested in harvest weed seed destruction can skip the tow-behind units entirely. Integrated versions of the Harrington Seed Destructor and a rival brand, the Seed Terminator, are now available. Both products were developed in Australia, and both attach to the combine. The Harrington Seed Destructor is powered hydraulically and uses a cage mill. The Seed Terminator is mechanically driven and uses a hammer mill.

Australian research has shown that the tow-behind and integrated Harrington Seed Destructors are equally effective at destroying weeds. That means Tidemann’s research on the tow-behind unit will apply to the integrated model as well.

About the author

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Editorial Director

Laura Rance is editorial director at Glacier FarmMedia. She can be reached at [email protected].

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