Weed of the Week: wild buckwheat

Wild buckwheat has long wound its way through producers’ crops and onto the list of the most obnoxious weeds in prairie fields.

Its long, ropey stems wrap around a combine’s reel or carry more crop than the machine can handle up the feeder. As a result, Agriculture Canada has classified wild buckwheat as producers’ third most common weed. In Alberta, it is the number one weed.

Canaryseed growers find that the distinctive, triangular seeds will cause grain to be rejected.

It can reduce cereal yields by up to 12 percent at a population of five plants per sq. metre, while flax yields can be reduced by 10 to 20 percent at five to 15 plants per sq. metre. The large seeds typically are higher in moisture than the crop and can compromise stored grain if in sufficient numbers.

The pest can evade a spring herbicide burnoff by germinating after the crop is up.

Later burnoffs should include additional active ingredients when this weed is present.

Significant reliance on Group 2 chemistries has allowed the pest to select for resistance to that herbicide family.

Seeds germinate all season, depending on moisture conditions.

Most begin life in the top five centimetres of soil, but they have been known to successfully germinate as deep as 20 centimetres in deep tillage.

A typical buckwheat plant will produce about 1,000 seeds, but 10,000 are possible if allowed to reach full maturity.

Research at the University of Saskatchewan showed that wild buckwheat seeds planted between April 15 and July 15 took an average of 17 days to emerge, 28 days to reach the first and second true leaf, 31 days to get to third true leaf, 50 days to make its first vine and 61 days to flower.

Most of the plant’s seeds will germinate the year after they are produced, but research has showed they can persist for several years. As a result, a single year of effective control might not be enough to manage an infestation.

The seeds persist in farm-saved seed and require thorough grain cleaning to remove. They can be particularly difficult in flax seed.

Buckwheat has a fibrous root system that can chase water and nutrients 80 centimetres into the soil, which makes it crop competitive and drought tolerant.

The plants will coil and creep along the soil until they find a suitable host to climb up out of the shade.

Most crops have an in-crop registered herbicide that will kill wild buckwheat early in the season or when it is small, but the weed is tolerant to MCPA and moderately tolerant to 2,4-D.

Group 2 resistance in wild buckwheat means that multiple modes of action through tank mixes or combination products can be critical.

Controlling buckwheat in non-herbicide tolerant broadleaf crops can be challenging. Clearfield options imazamox with imazapyr are a Group 2 choice with those genetics but would face challenges if resistance were present in the weed.

Chickpea, flax and sunflower growers can use a burn-off mix of glyphosate, carfentrazone and sulfentrazone to provide lasting control in those crops.

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