What’s the impact of a decade of herbicide resistant crops?
By Bruce Barker
Make more profit, reduce environmental impact.
Growers have voted with their feet, converting many acres over to herbicide
resistant (HR) canola, corn, wheat and soybean crops, so there must be an economic
benefit. But what about the agronomic and environmental impact? Based on published
research conducted by various scientists, Hugh Beckie, a research scientist
with Agriculture and Agri-Food Canada at Saskatoon, Saskatchewan, summarized
the impacts at the University of Saskatchewan's Soils and Crops Workshop in
"Globally, the movement to herbicide resistant crops has been large. In
2005, the US accounted for 55 percent of transgenic crops, followed by Argentina
at 19 percent, Brazil at 10 percent and Canada at six percent," says Beckie.
Herbicide resistant soybeans covered 60 percent of the global soybean acres,
while corn had 14 percent as HR crops. Globally, HR canola covered 18 percent
of canola acres, but in Canada, that jumps to about 95 percent of canola acreage
with HR as part of the Roundup Ready, Clearfield or Liberty systems. HR (Clearfield)
wheat and lentils are also registered in Canada, with Clearfield sunflowers
waiting in the wings.
How do the agronomics stack up?
Beckie says that back in 2000, a survey of HR and non-HR canola producers indicated
that yields of HR canola varieties averaged 10 percent more than non-HR canola.
The greater yields were attributed to higher yield potential and reduced weed
competition. On-going breeding efforts are also likely to continue to widen
the gap, as breeders focus on HR canola almost exclusively. In a survey of seedlot
samples, HR canola had improved seed quality with slightly greater oil content
and significantly less glucosinolates and chlorophyll content than non-HR canola.
|Net returns are 13 to 30 percent greater for HR than non-HR canola.
Photos By Bruce Barker.
On the other hand, HR soybeans suffered a yield drag of approximately four
percent, on average, in Ontario as shown in public variety trials from 2002
to 2004. The researchers there suggest the lower yield is likely due to differences
in genetics used to breed HR soybeans. However, in commercial fields, HR soybean
yields are often similar if not higher yielding because of improved weed control.
The latest varieties, however, have overcome this shortfall.
In corn, yields are similar between HR and non-HR crops. And in wheat, the
Clearfield CDC Imagine HR variety appears to have similar yield to the standard
non-HR check, AC Barrie.
What about the economics?
Several surveys and studies support the improved returns that HR crops deliver
to canola farmers. Beckie says that producer surveys conducted in 2000 found
net returns were 13 to 30 percent greater for HR than non-HR canola. Improved
yields, less dockage, improved seed quality, reduced herbicide costs and reduced
tillage costs contributed to the improved net returns. Another more recent study
by John O'Donovan with AAFC published in 2006 reported higher net returns for
Roundup Ready canola than herbicide regimes traditionally used in non-HR canola.
In Canada, less information is available on the economic benefits of HR soybeans,
corn or wheat. In surveys of soybean producers in Ontario and Quebec in 2002,
the main reason for growing glyphosate resistant cultivars was the reduced cost
of herbicide, labour and fuel. The national farm income benefit of transgenic
HR soybean and corn relative to non-HR cultivars from 1996 to 2004 has been
estimated at US$55 million and US$16 million, respectively by researchers Brookes
"In soybeans, HR varieties are well suited to no-till situations because
of the post-emergence weed control," says Beckie. "Those who don't
use HR soybeans seek identity preserved contracts for non-GMO varieties."
One of the largest criticisms of transgenic crops, levelled mostly by interest
groups outside of agriculture, is that HR crops only benefit developers and
farmers, but not society as a whole. Beckie says a study by Serecon Management
Consulting and Koch Paul Associates conducted in 2000 found that HR canola had
reduced herbicide use by 6000 tonnes in 2000, for about a 40 percent reduction
in total herbicide costs, and fuel consumption was reduced by 31 million litres
that year (12.6L/ha) because of less tillage, and so on.
Reduced fuel usage in transgenic HR vs. non-HR canola resulted in a reduction
in carbon dioxide emissions of 94 million kilograms from 1996 to 2004, according
to British researchers, Brookes and Barfoot. In addition, a reduction in carbon
dioxide emissions of 906 million kilograms during this period was attributed
to soil carbon sequestration as a result of less tillage in transgenic HR than
From 1995 to 2005, according to two independent studies, the environmental
impact (EI) per hectare, calculated using the environmental impact quotient
for individual herbicides and the amounts of active ingredients applied, declined
by 20 percent in HR vs. non-HR canola. This decline in herbicide use and EI
since introduction of HR cultivars was due to the use of herbicides at lower
application rates, a reduced number of applications and a decreased need for
Agronomic impacts on weeds
Beckie points to studies that show a general trend towards a shift in weed spectrum
for cropping systems utilizing HR canola. Generally, annual broadleaf weeds
like stinkweed have declined, along with fewer winter annual and perennial weed
problems. On the other hand, there has been a shift towards more wild oats,
green foxtail and volunteer cereals in HR canola.
HR crops are also an important tool in herbicide resistance weed management.
The inclusion of Roundup Ready and Liberty crops has meant that two more groups
are available for herbicide rotations. Group 9 (glyphosate) and Group 10 (Liberty)
herbicides have helped to better manage herbicide resistance to Groups 1, 2,
3 and 8, which all have cases of herbicide resistant grassy weeds documented
in western Canada.
"There is no resistance to Group 10 worldwide, so it has become a valuable
herbicide resistance management tool," says Beckie. "Glyphosate in
HR crops has also added another weed resistance management option." On
the other hand, Beckie cautions that growers need to follow good herbicide rotations,
even with HR crops. He says that frequent use of HR crops can select for new
HR weed biotypes, or aid the selection that has already occurred.
Has there been gene flow?
Gene flow, or the movement of the HR trait into other crops or weedy relatives,
has been speculated upon and sensationally reported as the escape of transgenics
into the natural environment. But does it really happen?
Beckie says gene flow can hypothetically occur if the crop species out-crosses.
In this case, if HR cultivars are grown in close proximity to non-HR cultivars,
HR genes may be transferred to non-HR plants and hybrid seed formed. HR crops
with out-crossing potential include canola, corn and, to a lesser extent, wheat.
The other way for gene flow to occur is through the physical transportation
of the seed, which can occur over long distances. "Gene flow via seed has
the potential to influence agriculture on a much larger scale than gene flow
via pollen," explains Beckie.
In canola, where out-crossing averages 30 percent and where more than one HR
trait has been developed, pollen gene flow can result in multiple HR volunteers.
Linda Hall of the University of Alberta first documented multiple HR canola
volunteers. In 1997 in northern Alberta, a field of Roundup Ready canola was
grown adjacent to a field of Liberty Link and Clearfield canola. Volunteers
with glyphosate resistance were found in 1998. These volunteers flowered and
produced seeds that contained individuals resistant with several two and three
way HR resistant traits. One three way herbicide resistant plant was found 550
metres from the pollen source.
Other canola studies, including one by Beckie in Saskatchewan in 1999, found
that gene flow ranged from 1.4 percent out-crossing at the field border to 0.04
percent at 400 metres away.
In corn, which is a highly out-crossing plant, maximum out-crossing of 82 percent
occurred in plants immediately adjacent to Bt transgenic corn, but declined
exponentially to less than one percent at 28 metres in research conducted at
Ottawa (by researcher Ma et al.) in 2004.
|HR crops have reduced the environmental impact of growing crops.|
In wheat, gene flow varies by cultivar, and research by Pierre Hucl at Saskatoon
found that gene flow remained below 0.5 percent and decreased over distance.
However, pollen-gene flow was still measured at 300 metres from the pollen source,
although at a low 0.005 percent.
Managing these HR crop volunteers has not proven to be difficult for most farmers.
Volunteer HR canola in cereals, for example, can be controlled with up to 30
different broadleaf herbicides that have an alternative mode of action. "Volunteer
canola is actually going down according to the last prairie weed survey,"
Another concern that is often raised is whether the HR traits can transfer
to weedy relatives in cropland. Beckie says numerous studies have investigated
this concern and essentially, the probability of gene flow from canola into
wild radish, wild mustard, or dog mustard is very low. In eastern Canada, though,
genes may disperse in bird's rape, but the increase in HR bird's rape would
likely only occur if herbicide use selected for them in cropland.
For corn, soybeans and wheat, no wild relatives are known to occur in Canada
and therefore, the hybridization between the crops and wild relatives is not
generally viewed as a bio-safety issue.
Scientists also looked at the potential for gene transfer into weeds in disturbed
or natural areas. Little difference was found between the ability of HR and
non-HR volunteers to compete in the absence of herbicide selection. As a result,
researchers have concluded that there is little likelihood of HR crops invading
natural areas, anymore than non-HR crops.
"Essentially, the invasion of HR crops into natural areas hasn't happened,"
says Beckie. There is no doubt that HR crops have become a mainstay in many
western Canadian farmers' crop rotations. With the economic and agronomic benefits
of varying degrees offered by HR crops, Beckie says farmers should follow good
agronomic stewardship to help ensure they are able to continue to reap the benefits
of the technology. And that scientists should continue to monitor the agronomic
and environmental impacts of the technology.
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