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86 DECEMBER 13, 2012 | WWW.PRODUCER.COM | THE WESTERN PRODUCER PRODUCTION
HERBICIDES | WEED RESISTANCE
Use herbicide tank mix against resistance: agrologist
Reducing risk | Glyphosate resistant kochia is spreading, but officials worry about resistant wild oats, green foxtail and cleavers
BY DAN YATES
SASKATOON NEWSROOM
Weed biologist Eric Johnson was
telling farmers as recently as a few
years ago to fight problematic weeds
with a higher rate of glyphosate.
The Agriculture Canada scientist
has since changed his message,
armed with a better understanding
of how weeds develop resistance to
commonly used herbicides and
knowledge of glyphosate-resistant
kochia on the Prairies.
At the Agri-Trend 2012 Farm
Forum Event in Saskatoon, Johnson
urged producers to guard against
herbicide resistance by tank mixing
herbicides with multiple modes of
action, especially in chem-fallowed
fields where resistant weeds are first
appearing.
“So even people that advise (farmers)
are a bit of the problem or contributed
to the problem,” he said in an
interview.
“And so there’s still a bit of that mentality
… but really, we should be tank
mixing.”
Officials announced earlier this
year that glyphosate-resistant kochia
had been discovered in three chemfallowed
fields in southern Alberta in
2011, the result of extensive use of the
Group 9 herbicide regularly applied
as Roundup.
Further survey work uncovered
more populations of resistant kochia
nearby and all signs point to the presence
of the weeds in 2012 at a location
further north in Alberta and a
few sites in southern Saskatchewan.
Johnson told the conference that
only 15 years ago scientists predicted
weeds wouldn’t develop resistance.
“I think we’ve learned as weed scientists
now to realize we’ll never say
that a plant won’t develop resistance
to herbicides because there’s so
many different ways they can adapt.”
Johnson said officials want to do
more extensive surveying for resistant
kochia in Saskatchewan. As a
tumbleweed, it produces large
amounts of seed and travels quickly.
“Kochia responds to the environment.
It likes dry, saline conditions,”
said Johnson.
“The last few years, it’s been wetter,
so it hasn’t been quite as predominant
and, I don’t think, quite as on
people’s minds. One dry year and it’ll
be back and they’ll remember how
serious it actually is.”
All kochia populations on the Prairies
are already assumed to be resistant
to Group 2 herbicides, which
spread quickly in a five-year period
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Tank mixing and multiple mode of action combination herbicides
are necessary to combat resistant weeds. | MICHAEL RAINE PHOTO
in the 2000s. Johnson said growers
must keep this in mind when tankmixing
herbicides to delay or manage
Group 9 resistant populations
because the Group 2 herbicide won’t
be an effective selection.
He said producers have several
options for tank mixes in wheat and
barley crops including dicamba,
Cleanstart and Blackhawk, although
he noted that 2,4-D alone won’t
effectively manage glyphosateresistant
kochia populations.
Growers have fewer options in
pulse and canola crops, but those
available include Cleanstart and
Amitrole 240.
Johnson is researching the use of
alternative Group 14 and 15 herbicides
on some crops.
“It does buy us time. We can’t lose
sight of those other things you have to
do that are important: good plant
density, competitive crops, crop
rotations,” he said.
“Those are very critical as well into
extending the life of our herbicides.”
Glyphosate-resistant kochia is
appearing in chem-fallow fields,
where Johnson recommended producers
tank mix with Cleanstart, a
Group 9 herbicide, or Distinct, a
dicamba product.
“I would like to talk to the growers
more in the infected area that are
chem-fallowing and discuss it with
them. I don’t want to come out and
say that you shouldn’t be doing this
because they are doing it for a reason
and it is a drier area and fallow has
been and probably will continue to
be a part of their system down there,”
said Johnson. “We might just have to
work on some options to reduce their
risk.”
Based on their abundance, officials
believe wild oats, green foxtail and
cleavers are the weed populations in
which glyphosate resistance may
appear in next.
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