Top Crop Manager

Features Agronomy Weeds
Saskatchewan weed survey indicates fewer weeds

Green foxtail, wild oats, wild buckwheat, Canada thistle and lamb's quarters in the top five.


November 19, 2007
By Bruce Barker

Topics

30aThe Saskatchewan weed survey conducted in 2003 brings encouraging news. While
the makeup of the weed community is relatively similar compared to the 1970s,
the overall densities have decreased – which is similar to observations
made in the recent Alberta and Manitoba weed surveys.

"That's the good news," says weed scientist Gordon Thomas with Agriculture
and Agri-Food Canada (AAFC) at Saskatoon. He says growers should not be discouraged
because weeds are not eradicated, but that should not be the goal anyway. Rather
the focus should be on economic control of weeds.

Thomas was the project leader for the 2003 survey, which was a collaborative
effort with Saskatchewan Agriculture, Food and Rural Revitalization (SAFRR).
Direct financial support was also received from the Matching Investment Initiative
of AAFC, and the pesticide and fertilizer industry. Alberta was surveyed in
2001 and Manitoba in 2002.

Advertisement

The survey was conducted on 2046 fields of spring wheat, barley, durum, oats,
canary seed, canola, flax, mustard, peas, lentil and chickpea. Conducted during
the summer, the survey reflects the weeds that were present in the field after
spraying, and the reason for their presence is varied. Although field personnel
were instructed to avoid newly germinated weeds, some of those counted may have
germinated after spraying in a second flush. Weeds may also have been present
because they escaped herbicide control or a herbicide that could have controlled
them was not used. A few organic producers were also involved in the survey.

A relative abundance value was calculated for each weed, using a combination
of frequency of fields, uniformity within the field, and density when they were
present as compared to the rest of the weeds. Relative abundance shows how a
specific weed ranked compared to all other weeds in the survey, rather than
what the impact of the weed was in the province. A weed with high densities
that occurs over entire fields and is found in most fields might be considered
a bigger problem than a weed that occurs at low densities, is patchy and is
only in the occasional field.

How the weeds compare
In terms of relative abundance and percent of fields in which they were present,
green foxtail, wild oats and wild buckwheat remained at the top of the weed
survey. Clark Brenzil, provincial weed specialist with SAFRR at Regina, says
that the survey was influenced by the abnormally hot and dry weather in 2002
and 2003 in many areas of Saskatchewan.

"The hot, dry weather favours C4 plants, such as green foxtail, that are
well adapted to these conditions," explains Brenzil. "If the survey
had been done in 2004, there could have been quite a difference in the relative
abundance rankings."

Brenzil says that in 2003, many crops struggled under drought conditions, resulting
in sparse crops with an open canopy. Under those conditions, C4 plants do well.
An example of how the weather influenced the survey was how very common C4 weeds
like lamb's quarters and redroot pigweed were found at more than twice the average
density in 2003 than those found in the 1995 survey when the environment was
cooler and wetter. Under cool conditions, C3 plants such as wheat, canola and
wild oats grow better.

Twelve weed species have been in the top 20 since the surveys began in the
1970s. Seven species have declined since the 1970s or 1986 survey including
wild rose, prostrate pigweed, night-flowering catchfly, cow cockle, bluebur,
pale smartweed and flixweed.

Pale smartweed, quackgrass and flixweed dropped just out of the top 20 from
1995 to 2003 and barnyard grass, volunteer flax and narrow-leaved hawk's beard
are new to the top 20.

In analyzing the survey, the devil is in all 342 pages of the report. For example,
while dandelion moved up two spots in the 2003 survey from the 1995 survey,
it is actually present in fewer fields; like getting a bigger portion of a smaller
Saskatoon pie. Such is the case with 13 of the top 20 ranking weeds including
the top seven ranking weeds. Only kochia and barnyard grass increased the proportion
of fields they occupied in the 2003 survey over 1995 numbers. Both are C4 plants.

Barnyard grass made the greatest territory gain, increasing the number of fields
it was found in from 3.3 to 8.7 percent of fields and moved from 28th place
up to 11th in relative abundance. It is now found throughout the south and has
spread into the central part of the province. Kochia continues to increase in
density in its historic range in the Palliser Triangle, and also appears to
be spreading north and east out from that range.

Other weeds that increased substantially were foxtail barley, annual sow-thistle
and prickly lettuce. "Prickly lettuce was a rare weed in the 1995 survey
and in 2003 it was present over much of the area south of Highway #1 and the
areas around Rosetown, Wynyard and Nipawin," says Brenzil.

Dandelion had a frequency (percentage of fields in which it was found) of 12.5
percent in 2004, compared to 18.3 percent in 1995. Field uniformity and average
density were similar between the years. That means dandelion management was
actually better in 2003 than 1995.

"When you look at the data, the highest value for dandelion density was
15 plants per square metre in 1995 and 27 plants in 2003. That could mean there
are a few more fields where dandelions are a big problem and the producer is
struggling to manage it. But most producers are using effective methods and
the overall trend in dandelions is toward fewer plants competing with the crop
when it really matters," says Brenzil.

On the other hand, canola slid in the rankings, but Brenzil sees some challenges
in the data. In 1995, the average density was about five plants per square metre
with the worst infestation at 66 plants. In 2003, the average density was similar,
but the worst density was 93 plants.

"That could be one of those situations were the odd producer is still
learning how to control Roundup Ready canola volunteers. They are easy to control
with 2,4-D but if you sit back and wait too long with post-emergence applications,
they can be difficult to control," explains Brenzil. "Another culprit
may be high harvest losses. Studies conducted by Dr. Steve Shirtliffe and former
graduate student Rob Gulden at the University of Saskatchewan indicate this
is often a problem."

The survey is summarized in a report that breaks down weed infestations by
crop, eco-region and crop, eco-district, extension region and crop, and extension
district. Brenzil says the data is valuable for local agronomists who would
like to see how weed communities are evolving in their area. By sifting through
the data in their area, they can keep track of emerging weed trends.

Greatest value will come in management survey
In addition to the weed survey, a farmer management survey was also conducted.
A 12 page questionnaire was sent to growers participating in the survey to collect
information on their farming practices. Those questionnaires are in the process
of being compiled. Thomas says that the Alberta survey is just being finalized
with around 700 tables in the report. Turning that data into information will
allow them to link the farming practices to the weed problems found in the fields.

While that information will be forthcoming over the next few years, Brenzil
says the take-away from the survey is that producers seem to be doing a good
job of managing their weed problems. The average density of annual grasses has
dropped from more than 30 plants per square metre in the 1970s to around 15
plants. Similarly, annual broadleaf weeds have dropped from around 18 plants
per square metre to around six plants. Winter annuals and perennial weeds have
declined as well, although not as dramatically.

"The weed pressure in fields is down substantially. We are seeing more
weeds in patches, in fewer fields, with a few exceptions. And in those patches,
the populations are down as well," says Brenzil. "That makes sense
when you look at some of the changes in farming practices. With direct seeding,
the weeds are spread around the field less and the weed population is depressed.
You won't eliminate weeds, but we are seeing a declining population and hopefully
this is resulting in a lower overall impact on crops and the returns that farmers
get from them."

Old technology fits new weed issues
Weed problems like kochia, wild oats and risk of resistance
to Group 1 and Group 2 herbicides still can be managed by some of the
older crop protection technology.

For pea, bean, lentil and sunflower crop protection, Edge, a Group 3
product containing ethalfluralin can hold the key for resistant weed management.
"It may be the best alternative for growers who need to rotate out
of the Group 1 or Group 2 products," says Brian Wintonyk, Dow AgroSciences
customer agronomist in Calgary.

"Group 2 herbicides initially had good activity on kochia,"
he points out. "However, due to the high selectivity of those herbicides,
kochia resistance has emerged as a significant problem in the past three
to five years."

Edge hit the market in 1987 and was very popular prior to the introduction
of herbicide tolerant canola. The alternate mode of action can greatly
reduce the risk of resistance development. "If fields already have
kochia or wild oats that's resistant to Group 1 and Group 2 products,
Edge can help manage the concern before it becomes worse," says Wintonyk.
"The best strategy, though, is to rotate herbicide groups and prevent
the development of weed resistance."

Works in no-till
Both no-till and conventional tillage growers can successfully use Edge.
The typical approach is to incorporate Edge three to four inches deep,
either in fall or spring, as a base treatment to control early emerging
weeds in peas, beans or sunflowers. It also is approved as a fall-applied
treatment prior to lentils.

"In some regions, where growers practice reduced tillage for at
least two years with less than 30 percent soil disturbance, they apply
Edge to the soil surface," Wintonyk says. "They blend it into
the soil surface with a very shallow harrow operation to ensure there's
good granule-to-soil contact and still get effective weed control."

When Edge is applied in this manner, he notes, a pre-seeding burndown
treatment is still needed. "Edge controls germinating weeds, not
emerged weeds." Once Edge has been activated with warmer temperatures,
it offers underground control of a wide variety of weeds over an extended
period of time.

For protection in wheat or barley, Group 4 products Attain and Prestige,
can address the challenge of weed resistance by offering a Group 4 mode
of action, Wintonyk says.

Attain and Prestige are fluroxypyr-based and with a combination of other
active ingredients. They are applied post-emergence and can be mixed with
most grass herbicides. Both have excellent control of kochia and a wide
array of broadleaf weeds.

Resistance prevention by rotating herbicides is a producer's best management
practice. Considering all the herbicide tools, both old and new increases
a producer's options.

 


Print this page

Related



Leave a Reply

Your email address will not be published. Required fields are marked *

*