Top Crop Manager

Features Agronomy Identity Preserved
Atrazine assessment yields interesting results

Value is set to dissuade North American ban.

November 12, 2007  By Top Crop Manager

42aDespite developments in new chemistries during the past decade, the use of
atrazine in corn has become a standard for growers in Ontario. At the same time,
the registration of atrazine is under an ongoing review in Canada, the US and
other parts of the world. In fact, atrazine has been de-registered in France
where higher rates than those used in Ontario were the norm, leading to environmental
concerns. It has been banned in seven European countries and is undergoing continued
environmental risk assessments in North America, with some favourable re-evaluations.

The reason for the ban in Europe is for its impacts on an environmental level.
However, it should be noted that rates have been considerably higher in Europe,
approaching twice the application rates approved for use in Canada. In the US,
those rates are also at nearly twice the Canadian rates.

In 2003, the Ontario Ministry of Agriculture and Food conducted a survey of
pesticide use and found that atrazine accounted for 32.7 percent of all herbicides
used in corn. That figure was estimated to represent 80 percent of its use in
1998. Furthermore, the introduction of new herbicides for corn has often required
tank-mixes using atrazine. "Clearly, atrazine continues to be a required
weed management tool in field corn," says Dr. Clarence Swanton, professor
and chair of the Plant Agriculture Department at the University of Guelph. "Of
course, the concern is that if it's been banned in Europe, that same ban could
come to North America and the question then becomes, 'is there a replacement
for atrazine?'"

To answer this, a study was conducted from 2002 to 2004 at Elora and Woodstock
research stations, and compared four pre-emergence and four post-emergence herbicides,
alone and with atrazine. According to Swanton, the goal was to determine the
agronomic and economic impacts of atrazine, and its specific importance to the
Ontario corn industry.

Findings fairly conclusive
Overall, the study's findings showed the addition of atrazine increased average
yields by eight percent with pre-emergence programs compared to five percent
with post-emergence treatments. The addition of atrazine improved yields an
average of 6.5 percent in all pre-emergence and post-emergence herbicide programs.
"In all, this represents an estimated net benefit in production of 357,000
tonnes of grain corn with a value of $45.7 million annually to Ontario corn
producers," says Swanton. These figures are based on 2002 corn production
statistics from OMAF and a cost of atrazine set at $12.80 per hectare ($5.12
per acre).

In the field studies, the most commonly used herbicide programs in Ontario
were used, including Fieldstar (flumetsulam/clopyralid), Banvel II (dicamba),
Callisto (mesotrione), Converge (isoxaflutole), Striker (flumetsulam/clopyralid/2,4-D)
and Peak Plus (prosulfuron + dicamba). In all herbicide treatments, Dual II
Magnum (s-metolachlor/benoxacor) was applied as a pre-emergence treatment for
control of annual weeds. In all trials, the species composition was typical
of that found in corn fields in southern Ontario. Common lamb's quarters and
wild buckwheat were present in all six trials, with redroot and green pigweed
in five, and wild mustard and common ragweed present in four trials.

Atrazine made the difference in most
its own, atrazine provided commercially acceptable (90 percent) control of wild
mustard, wild buckwheat and pigweed. It did not fare as well on its own against
lamb's quarters or common ragweed. All treatments without atrazine, save one,
failed to provide acceptable control of at least one weed species, yet all gave
acceptable control with the addition of atrazine. "All pre-emergence treatments
without atrazine failed to provide acceptable control of three or four of the
five weed species present," explains Swanton. "The addition of atrazine
improved overall weed control with pre-emergence treatments, particularly the
control of lamb's quarters, wild buckwheat and common ragweed."

The addition of atrazine also improved control of wild mustard with Banvel

In post-emergence treatments, those without atrazine were more effective. "Banvel
II gave 96 to 97 percent control of all weed species," says Swanton. All
other post-emergence treatments failed to control at least one species, and
the addition of atrazine improved wild buckwheat control with post-emergence
treatments of Striker and Peak Plus, and improved common ragweed control with

The bottom line on this study is that corn growers in Ontario are generally
better off with atrazine than without, a concern for Swanton, given the ban
in Europe. But he is hopeful the economic impact in the study is sufficient
to withstand a challenge, along with continued study by the US Environmental
Protection Agency and Canada's Pest Management Regulatory Agency.

The challenge in that scenario comes from two fronts: there are no new herbicides
to come in the near future and, as a result, it becomes a mystery as to where
growers will turn when Banvel II begins to show signs of resistance.

However, even with the Banvel II treatment, yields were improved with the addition
of atrazine.

The Bottom Line
We have all learned a thing or two about chemical synergy and
tank-mixes, and also about the different modes of action in today's chemical

Atrazine works as well, or better, with other chemicals as it does by
itself. Even Roundup, if tank-mixed with atrazine, is more a cost effective
single pass corn spray, than if Roundup is used just by itself.

I would think there would be many, many disappointed corn growers in
this country if atrazine were to be banned in North America. Andy
van Niekerk, Stayner, Ontario.

Atrazine can be a very valuable tool in the management of weed control,
is both agronomically and financially. We, as farmers need to be very
diligent with our herbicide programs to stop weed resistance and keep
the cost in line with the price of corn today. Grahame
Hardy, Inkerman, Ontario

This is one chemical we cannot do without. Everyone used to be a big
atrazine user: it was part of the corn revolution. We have wild mustard
which Banvel II will not touch, but the atrazine deals with it. There
is talk that it enhances the activity of the tank-mix partner.
Lennie Aarts, Wainfleet, Ontario

For 10 years I have tank-mixed it with Prowl. The results with this combination
is 90 to 95 percent effective for broad spectrum control.

Without atrazine, I would consider using Banvel II tank-mixed with Prowl
or Fieldstar. If atrazine was not available, my cost per acre would increase
$7 to $9 more per acre. Tony Pynenburg, Bright,

Atrazine is an invaluable herbicide for the Ontario corn crop. In today's
market, atrazine is mostly used as a tank-mix partner with another herbicide.
This management technique is an effective way to achieve excellent weed
control while keeping our environment's safety at the top of our priority
list. Leo Guilbeault, Belle River, Ontario.



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