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Weeds and tillage systems – trends in western Canada

Overall, weed densities across the prairies are reduced and winter annual weed pressure declines, according to a recent AAFC weed survey.

November 27, 2007
By Donna Fleury

Wild oats: still the most troublesome weed.

Provincial weed specialists, in conjunction with researchers at Agriculture
and Agri-Food Canada (AAFC) have conducted surveys of crop production practices
across the prairies; in 2001 in Alberta, 2002 in Manitoba and 2003 in Saskatchewan.
These surveys of producers growing the major types of cereal, oilseed and pulse
crops addressed a broad range of questions surrounding weeds, weed management
and other agronomic practices used on farms.

"Approximately 2200 questionnaires were completed by producers across
western Canada," explains Gordon Thomas, research scientist with AAFC in
Saskatoon, Saskatchewan. "We've summarized much of the data we received
from producers and are now moving into the analysis stage." Thomas will
be integrating all of the information into a database and will try to use the
information to help explain current and future weed management questions. "This
database will form a basis for future research and extension activities across
western Canada."

Generally, Thomas found that weed densities are down and weeds are shifting
in terms of relative abundance. While some classes of weeds are increasing,
others are declining. For many farmers, wild oats and wild buckwheat are at
the top of the list of troublesome weeds, along with Canada thistle, kochia
and others. Tillage practices, in particular the move to more reduced tillage,
has brought about some of the shift in weed populations.

Table 1. Percent of
producers using conventional tillage and direct seeding in Alberta, Saskatchewan
and Manitoba AAFC Weed Survey. Sample size = 1849.
Area Conventional Direct seeding
Grasslands (a) 42 58
Aspen Parkland and Lake Manitoba Plain (b) 71 29
Boreal Plains (c) 53 47
All 59 41
(a) Grassland eco-regions: includes mixed grassland,
moist mixed grassland, fescue grassland (Brown and Dark Brown soils).
(b) Aspen Parkland and Lake Manitoba Plain
eco-regions (Black soils).
(c) Boreal Plains eco-regions: Boreal Transition
and Interlake Plain (Dark Grey and Black soils).
Note: Peace lowland eco-region was excluded
from the summaries because of the small number of direct seeding respondents.
The 2001 Statistics Canada Census breakdown
of seeding practices across the prairies differs from the AAFC data, but
the trends are similar.
2001 Census breakdown of seeding practices
(percent farmers).
Tillage incorporating most of the
crop residue into the soil
Tillage retaining most of the crop
residue on the surface
No-till seeding
Manitoba 54.5 32.6 12.9
Saskatchewan 32.5 28.8 38.7
Alberta 37.1 35.5 27.5
Prairies 37 31.5 31.5
Source: Statistics Canada.

Thomas went through the database and produced this selected overview of the
most troublesome weeds according to tillage system across the prairies. For
the survey, direct seeding is defined as a system with no fall or spring tillage
prior to seeding, and includes both low disturbance and high disturbance seeding
equipment. The remaining data were placed in the conventional tillage category,
which includes fall and/or spring tillage.

In Tables 2, 3 and 4, developed specifically for
Top Crop Manager magazine,
Thomas presents the 10 most troublesome weeds in each system. The weeds are
not presented in ranked order of importance.

Three weed species that seem to be responding more strongly than other species
to the type of tillage system are kochia, chickweed and stinkweed. Kochia was
ranked the number one weed by 11.7 percent of respondents using direct seeding
as compared to 4.3 percent of those using conventional tillage. Kochia was ranked
in the top five troublesome weeds by 31.2 percent of direct seeders, and 14.8
percent of those using conventional tillage. Chickweed was more troublesome
for conventional tillage systems, with 9.9 percent of respondents ranking it
as one of their top five, compared to only 1.9 percent of direct seeders. Stinkweed
was ranked as one of the top five by 21.5 percent of those using conventional
tillage, as compared to 31.5 percent of direct seeders.

Table 2. Percent of
producers listing specific weeds as troublesome by tillage system in the
Grasslands eco-regions of Alberta and Saskatchewan.
Troublesome weed Conventional Direct seeding
Wild oats 68 70
Wild buckwheat 47 50
Kochia 44 62
Stinkweed 34 37
Green foxtail 23 30
Russian thistle 21 21
Canada thistle 19 15
Cow cockle 16 10
Flixweed 14 18
Wild mustard 12 11
Source: Thomas, AAFC.

Thomas will continue with the analysis of the information and producing summary
reports for each province. "We will be working with researchers and extension
staff to answer specific questions on current and future weed issues,"
says Thomas. "With this information, we can help the industry find commonalities
between weed populations and management practices, and provide answers to producers."


"In Manitoba, we're seeing the emergence of two main groups and cropping
management," explains Dr. Rene Van Acker, associate professor of weed science
with the University of Manitoba. "We're seeing one group that is very intent
on increasing the size of their farming operations and are pushing hard for
simple, effective weed management systems." Many of these farmers are concerned
about resistance and one of the key tools for management is herbicide tolerant
canola in rotation.

"The other emerging group, which may include big or small farms ranging
from certified organic to more traditional operations, are much more interested
in a holistic weed management approach," says Van Acker. They are learning
more about the effect of rotation on weed management, and finding ways to make
their systems more biologically functional by integrating diversity into the

Table 3. Percent of
producers listing specific weeds as troublesome by tillage system in the
Aspen Parkland and Lake Manitoba Plain eco-regions of Alberta, Saskatchewan
and Manitoba.
Troublesome weed Conventional Direct seeding
Wild oats 71 70
Wild buckwheat 45 48
Canada thistle 39 47
Green foxtail 30 26
Wild mustard 18 12
Stinkweed 18 25
Cleavers 13 11
Redroot pigweed 11 5
Hempnettle 11 5
Quackgrass 11 13
Kochia 5 13
Volunteer canola 9 11
Source: Thomas, AAFC.

"The first group is trying to survive by sheer volume, while this second
group is trying to survive by a more knowledge based approach and a biologically
functional system that is inherently less dependent on the two key external
inputs: nitrogen fertilizer and herbicides. These two groups are not mutually
exclusive and we hope the trend will be for one group to emerge with everyone
interested in having systems that deliver what is needed in terms of pest management."

Another emerging category is 'service crops', which are not harvested for yield
but rather for benefits such as weed control and disease management, nitrogen
fixation and other benefits to the soil. "Farmers are looking to move away
from a simple mono-culture, to building a system that is a bit more biologically
diverse, but doing so in an economic fashion," says Van Acker.

Overall, some of the key weed trends in Manitoba include an increase in Canada
thistle, dandelion and kochia. Group 2 resistance is one of the key concerns
for farmers, with Group 2 resistant kochia an increasing problem. Group 1 resistance
continues to be a concern. "Farmers are very aware of herbicide resistance
and rotation of herbicide groups as part of their weed management."

Table 4. Percent of
producers listing specific weeds as troublesome by tillage system in the
Boreal Plains eco-regions of Alberta, Saskatchewan and Manitoba.
Troublesome weed Conventional Direct seeding
Wild oats 70 62
Wild buckwheat 47 44
Canada thistle 42 33
Green foxtail 25 23
Stinkweed 23 33
Kochia 19 28
Cleavers 12 7
Chickweed 12 1
Dandelion 11 11
Hempnettle 11 3
Wild mustard 10 14
Flixweed 5 11
Quackgrass 10 11
Source: Thomas, AAFC.


In Saskatchewan, there is a higher overall trend towards annual grasses and
perennial weeds. "It shows that farmers are managing their broadleaf weeds
quite a bit better than in the last survey completed in 1995," says Clark
Brenzil, provincial weed control specialist with Saskatchewan Agriculture and
Food. "We've also had a lot of new herbicide products in general, particularly
for crops like pulses and canola."

Brenzil adds, those looking at this survey have to understand that the weed
count data is taken after all management activities have been conducted. As
a result, the weed numbers and trends can represent the state of weed management
technology more than the presence or absence of specific weeds.

The shift to more direct seeding has also changed the weed populations. "You
tend to get a more even emergence of weeds under direct seeding because they
aren't spread out at different depths," says Brenzil. There will be a more
consistent one-off flush of those weeds, rather than seeing emergence extended
over a couple of weeks. "That makes timing of herbicide applications much
easier and more effective."

Farmers are managing weeds as part of their overall management practices. "Although
weed management is important, it is only part of everything farmers do to maximize
their income," says Brenzil. "The bottom line is don't manage weeds
for your neighbours, you have to manage for your banker." Early weed control,
good crop and herbicide rotations are key to integrated management.


With the increase in reduced tillage, certain weeds are becoming more common
than they used to be. "We're definitely seeing an increase in perennials,
such as Canada thistle, quackgrass and dandelions," says Paul Laflamme,
regulatory and risk management specialist with Alberta Agriculture, Food and
Rural Development. "A few annuals, cleavers and annual sowthistle in particular,
are showing up with increasing frequency." At the fall 2005 Alberta Weed
Advisory Committee meeting, foxtail barley was discussed as another weed that
was becoming more problematic in cropping areas and requiring additional research.

The trend towards more reduced tillage continues, particularly with the rising
fuel prices. "I've talked to a lot of farmers this fall that are trying
to shift their management to a one pass seeding operation," says Laflamme.
"The price of fuel has had a big impact and farmers are looking for ways
to reduce passes and reduce fuel inputs."

Overall, the trends in Alberta are away from annual weeds towards more perennial
weed problems. This shift is to be expected when tillage practices change. "Farmers
are managing and controlling these weeds using good management options including
proper crop and herbicide rotations," says Laflamme. "They are very
aware of herbicide resistance issues and ensure those herbicide rotation strategies
are built into their integrated management plans."

The four tables provided by AAFC
were developed specifically for this article – they have never been
published anywhere else to-date.