Making the most of residuals

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Grassweed control in wheat can be markedly improved by better use of residual herbicides this autumn, according to the latest evidence from Agrii’s integrated crop management research programme. And not just by using extra flufenacet or more complicated herbicide stacks or sequences either.

Instead, application timing, spray settings and multi-functional adjuvants all have equally important roles to play in making the most of crucial residual chemistry, the research-led agronomy company insists.

“As residuals have become more and more vital in controlling black-grass and ryegrass so it has become more and more essential to use them in the most effective ways possible alongside all the cultural controls in our armoury,” pointed out Agrii regional technical adviser, Will Foss. “That way we maintain their activity, not to mention our freedom to use them.

“The key weather factors affecting residual activity are moisture which determines herbicide uptake, and temperature and sunlight which affect persistency. So, as well as giving time for the most effective pre-planting control of grassweeds, we find invariably later-autumn sowing also means better residual herbicide efficacy.

“Our work suggests October drilling just as soil temperatures begin to decline into ‘magic’ single figures results in the best persistency. Combine this with firm, fine seedbeds and pre and peri-em residuals with a range of solubilities and persistencies and you have the best recipe for dealing with problem weeds regardless of soil moisture levels.”

While Will Foss agrees that flufenacet needs to be at the heart of most black-grass and ryegrass control programmes, he is adamant that partnering it with complementary actives is essential both for the greatest efficacy and to guard against resistance development.

As well as a different mode of action, diflufenican is especially valuable here for its lower solubility and much greater persistence.

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