Weed Management
Control of Difficult to Manage Weeds in Ontario Corn
By Peter Sikkema, University of Guelph, Ridgetown College
Ken Hough, OCPA Director of Research and Market Development
Over the past three years,
OCPA has provided funding ($15,000 per year) to Peter Sikkema, Ridgetown Campus of the University of Guelph, to
evaluate various herbicides for control of ‘difficult-to-manage’ weeds. Generally, the species studied are perennial
weeds, and are most prevalent in reduced-till cropping systems, although they may occur in conventional tillage
programs as well. Although many of the species studied are relatively isolated in their occurrence (i.e., they
do not affect a large proportion of Ontario’s corn acreage), nevertheless, where they do occur they often cause
serious yield loss and make crop management much more difficult. The development of effective weed management strategies
in a corn/soybean/wheat rotation may mean the difference between profit and loss for growers who have these weeds
on their farms.
A
summary of the results follows. Where a particular weed species was tested in
both corn and soybeans in 2000, information on control in soybeans has been included
as well. (Some weeds, such as three-seeded mercury, biennial wormwood and dandelion,
were tested in soybeans but not in corn, so results are not presented here).
Spreading Atriplex
Glyphosate applied alone preplant in no-till corn provided poor full season control of spreading atriplex, while
all the glyphosate tankmixes evaluated provided good to excellent full season control (glyphosate + Converge, glyphosate
+ Fieldstar, glyphosate + Banvel II and glyphosate + Marksman).
Glyphosate applied alone preplant in no-till soybeans provided poor full season control of spreading atriplex,
while excellent control of spreading atriplex was obtained with preplant tankmixes of glyphosate + Broadstrike
Dual or glyphosate + Sencor/Lexone. Postemergence, glyphosate in Roundup Ready soybeans provided excellent control
of spreading atriplex while in conventional soybeans, none of the herbicides available provided consistent control,
although Pinnacle has shown more activity than the other herbicides evaluated.
Swamp Smartweed
In trials conducted over the past 10 years at Ridgetown College, none of the postemergence herbicides available
have provided consistent control of swamp smartweed. Herbicide programs including dicamba (Banvel II, Distinct
and Marksman) have provided the best control.
Hemp
Excellent full season control of volunteer hemp in corn was obtained with atrazine, Distinct, Marksman, Pardner
+ atrazine and PeakPlus. Glyphosate and Liberty provided excellent control of volunteer hemp in Roundup Ready and
Liberty Link corn respectively.
Bentazon provided excellent control in conventional soybeans, while good control was obtained with Blazer and Pinnacle.
Canada Fleabane
Glyphosate applied alone preplant, plus all the glyphosate tankmixes evaluated (Converge, Fieldstar, Banvel II
and Marksman), provided excellent control of Canada fleabane in corn. The best postemergence control of Canada
fleabane in corn was provided by the dicamba-based herbicides (Banvel II, Distinct and Marksman). Glyphosate provided
excellent control in Roundup Ready corn, and Liberty provided excellent control in Liberty Link corn.
FirstRate and Classic provided the best postemergence control of Canada fleabane in conventional soybeans while
glyphosate provided excellent control in Roundup Ready soybeans.
Crab Grass
All the preemergence (Dual II Magnum, Primextra II Magnum, Frontier, Prowl and Converge) and post-emergence (Elim,
Accent and Ultim) treatments that were tested provided good to excellent control of crab grass in corn.
All of the postemergence treatments (Venture II, Assure II, Excel Super, Select, Poast Ultra and Roundup Transorb)
evaluated for crab grass control in soybeans provided good to excellent control with the exception of the late
application of Poast Ultra.
Sandbur
The preemergence application of either Primextra II Magnum or Converge provided good control of sandbur in corn
at only one of two locations. Other preemergence treatments (Axiom, Dual II Magnum, Frontier and Prowl) provided
poor control. The postemergence applications of Elim, Ultim and Accent provided good control at both locations.
Bur Cucumber
Management of bur cucumber in corn should begin with a soil-applied application of atrazine, but this will not
provide full season control. This can be followed with a postemergence application of Pardner + atrazine, which
will provide almost full season control of this weed. Data from Pennsylvania State University indicates that PeakPlus
and Summit also have activity on this weed.
Bur cucumber can be controlled in Roundup Ready soybeans with glyphosate. The best control in conventional soybeans
has been with Classic, Pinnacle and Reliance.
Field Horsetail
The tankmix of Ultim + Striker (Ultimax) has provided fairly consistent control of field horsetail in corn. There
has been some variability in the results which is thought to be due to different biotypes across Eastern Canada.
All of the preplant herbicide treatments evaluated (glyphosate or Amitrol 240 tankmixed with Broadstrike Dual)
provided good to excellent full season control of field horsetail in no-till soybeans.
Horsenettle
All of the herbicide treatments evaluated (Ultim + Banvel II, Ultim + Distinct, Ultim + Marksman, Ultim + PeakPlus,
Ultim + Striker and Accent + Summit) provided good to excellent full season control of horsenettle across 3 sites
in corn in 2000.
A single application of glyphosate provided good control of horsenettle in Roundup Ready soybeans. In conventional
soybeans, FirstRate was the product of choice.
Perennial Sowthistle
Summit provided excellent full season control of perennial sowthistle in corn. Atrazine + COC and Marksman provided
very good control, while the Banvel II and Distinct treatments provided good control of perennial sowthistle.
A sequential application of glyphosate provided excellent control of perennial sowthistle in Roundup Ready soybeans.
Annual Sowthistle
All the postemergence treatments tested (atrazine + COC, Banvel II, Distinct, Marksman, Shotgun, Pardner + atrazine,
PeakPlus and Summit) provided excellent control of annual sowthistle in corn.
Classic, Reliance STS, Viper, Meridian Plus and glyphosate all provided excellent control of annual sowthistle
in soybeans.
Proso Millet
A preemergence application of Converge provided good to excellent full season control of proso millet in corn.
A postemergence application of Ultim provided excellent control, while Elim or Accent provided good to excellent
proso millet control.
A single application of glyphosate, Venture II, Assure II, Excel Super, Select or Poast Ultra provided excellent
control of proso millet in Roundup Ready soybeans.
Note that information on herbicide rates used in these tests, and/or use of adjuvants, etc. are not included above.
Also, most of these herbicides have not been registered for use on these species in corn. Growers interested in
further information should visit Mr. Sikkema’s website: www.ridgetownc.on.ca/weeds
or you can connect from gocorn.net.
Sufficient data has been compiled to date to proceed with applications for a User Requested Minor Use Label Expansion
(URMULE) for each of the following weed species/control options:
• Ultim for control of sandbur in corn
• Distinct for control of perennial sowthistle in corn
• Distinct for control of prickly lettuce in corn
• Distinct for control of Canada thistle in corn
• Banvel II for control of Canada fleabane in corn.
OCPA will be assisting in these label expansion requests.
Control of horsetail now appears on the Ultimax and Striker product labels as the result of a previous request
based on Mr. Sikkema’s research.
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