Wild buckwheat, or polygonum convolvulus, is an annual weed that reproduces by seed. The long, weak stems trail on the ground or twine around other plants. Heart-shaped, pointed leaves are a distinctive feature. Wild buckwheat is particularly troublesome because of its climbing nature. This weed entangles crop plants and can cause crop lodging. It makes swathing and combining difficult as it becomes entangled in machinery.
The Canola Council of Canada recommends a four-year rotation for cultural control of wild buckwheat. This puts wild buckwheat in same league as tough pest problems such as sclerotinia stem rot, blackleg, alternaria black spot, root rot complex, root maggot and green foxtail.
WHY WILD BUCKWHEAT HAS A PROBLEM IN GLYPHOSATE-TOLERANT CANOLA
 In field after field, growers are seeing that the 0.5 of a litre per acre rate of Roundup_ offers only marginal control of wild buckwheat. This is to be expected, since in other situations, such as chemfallow, you need to use a higher rate of glyphosate (0.51 to 0.77 L/ac) for wild buckwheat control. The recommendation goes further - to use the higher end of that rate range for wild buckwheat at the 3- to 4-leaf stage.
That's exactly the kind of staging problem that can arise when the canola is sprayed early to eliminate early weed competition, especially from wild oats. Later-emerging wild buckwheat can then get to the 3- to 4-leaf stage, or beyond, where an additional 0.5 of a litre per acre application provides little control.
ECLIPSE* GETS THE WEEDS GLYPHOSATE MISSES
As a company that now provides both glyphosate and selective herbicides, Dow AgroSciences has evaluated ways to improve weed control in glyphosate-tolerant canola.
Eclipse is a new weed control solution for use by glyphosate-tolerant canola growers who are not completely satisfied with the results of one or two half-liter applications of glyphosate.
Along with the broad-spectrum weed control you expect from a glyphosate-tolerant canola herbicide, Eclipse gives you the convenience of a one-pass solution for wild buckwheat, dandelion and other tough weed problems.
It not only brings wild buckwheat control up to your expectations, but also opens the staging window by allowing control up to the 6-leaf stage of wild buckwheat.
PRE-EMERGENTS REMAIN AN OPTION
However, the wild buckwheat control that pre-emergent Edge* and Treflan* used to provide has not always been matched in the new canola-growing systems. And the grassy weed herbicide rotation option they provided has come to be missed by many growers. Edge and Treflan are both Group 3 herbicides.
If wild buckwheat is a problem in your canola fields, Edge and Treflan are still available and can still be used as a base treatment in all varieties of canola, conventional, herbicide-tolerant canola and Nexera* varieties.
SURFACE APPLICATION OF PRE-EMERGENTS
There is considerable evidence that tillage incorporation of pre-emergents may not be required in reduced tillage situations. Numerous research trials and farm-scale tests have found that surface application can be a practical, cost-effective method of controlling weeds in direct seeded fields. While research and experience on surface application is advancing, this method of application is not registered at the time of writing. This is a basic introduction to the practice of surface application:
- Spread residue thoroughly with the combine when harvesting the previous year's crops. Clumps of chaff will reduce herbicide effectiveness by variable amounts.
- For best results, surface-apply only to fields which have been direct seeded (with 30% or less disturbance) for at least two years prior to using surface-applied pre-emergents.
- Spread the granules evenly using a properly calibrated applicator, and then harrow to trap the granules in the surface layer.
- Make a spring burnoff with Vantage* Plus or Vantage part of your application plan, because this combination provides better control than either product alone.
- Use the granular formulation, because it falls through residue, allowing the active ingredient to attach to soil particles. Liquid formulations can be tied up in crop residue.
- Keep soil disturbance to less than 30% during seeding operations.
- Use the existing label rates appropriate for fall or spring application.
Sources:
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