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 Impact mills, which destroy weed seeds picked up by a combine,
have been shown to kill 70-99% of weed seeds in soybeans, wheat,
and other small-statured cropping systems. And a recent Weed
Science study from the University of Illinois shows even seeds
that appear unscathed after impact milling don’t germinate the
following spring.
“Harvest weed seed control is really becoming an accepted part
of integrated weed management,” says Adam Davis, study co-author
and head of the Department of Crop Sciences at U of I.
“Producers are excited about it.”
In the current study, Davis and his collaborators wanted to see
how the Harrington Seed Destructor (HSD), an impact mill
developed and widely used in Australia, handled common U.S.
agronomic weeds without the complications of real field
conditions.
The researchers collected seeds from 10 common weed species in
soybean fields in the U.S. Midwest and Mid-Atlantic regions.
They fed the seeds through a stationary HSD, and then tried
germinating them in a greenhouse and in the field following a
typical Illinois winter.
Davis says 0 to 15% of the seeds appeared to be undamaged
immediately after milling, regardless of species and seed size.
But when the undamaged seeds were buried in the field and left
through the winter, fewer than 10% survived. “Basically, almost
zero survived overall.”
Based on his previous research, Davis thinks microscopic
abrasions from the impact mill damage the seed coat enough for
microbes to enter and destroy the embryonic weed inside.
Can producers expect nearly zero weed seed survival when using
the HSD or other impact mills in the field? Probably not. Davis
and his collaborators have been conducting U.S. field trials
with the HSD for five years, and typically see a reduction in
weed seed rain by 70 to 80%.
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“The difference between its efficacy as a stationary
device and its efficacy in the field is largely due to shattering of
the weeds,” Davis explains. “As the combine is going through, it's
shaking everything and causing a lot of seed dispersal. By looking
at the HSD as a stationary device, we’re able to quantify the
theoretical max.”
Whether impact mills kill 70 or 99% of weed seeds, non-chemical
control strategies are important in slowing the evolution of
herbicide resistance. However, over-reliance on any one strategy
could select for additional problematic traits in weeds.
“If producers start using this device on a large scale, they will
ultimately select for earlier shattering. It’s already been shown in
Australia,” Davis says. “That's just the nature of weed and pest
management in general. Really what you're doing is managing
evolution. In order for any tactic to be successful, you’ve got to
change it up. You need to confuse them; add diversity in the time of
year and life stages you're targeting. We're just proposing this as
a new tactic that's effective – not the only tactic.”
The article, “Fate of weed seeds after impact mill processing in
Midwestern and mid-Atlantic United States,” is published in Weed
Science [DOI: 10.1017/wsc.2019.66]. Co-authors include Lovreet
Shergill, Kreshnik Bejleri, Adam Davis, and Steven Mirsky. The
research was supported by USDA-ARS.
The Department of Crop Sciences is in the College of Agricultural,
Consumer and Environmental Sciences at the University of Illinois.
[Source: Adam Davis,
News writer: Lauren Quinn]
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