Herbicides

Page last updated: Wednesday, 11 November 2020 - 9:16am

Knockdown herbicides for fallow and pre-sowing control

Knockdown herbicides (or non-selective) kill all plants when used in sufficient quantities, under suitable environmental conditions.

Benefits

  • Knockdown herbicides effectively kill weeds and are cost-effective.
  • Use of knockdown herbicides can improve the timeliness of sowing.
  • Use of knockdown herbicides rather than cultivation will reduce the risk of erosion, improve soil structure and improve plant available soil water content.

Issues

  • Consider the suitability of herbicide use for fallow or pre-sowing weed control by assessing environmental conditions.
  • Stressed weeds will not be adequately controlled by knockdown herbicides.
  • Overuse of knockdown herbicides will select for resistance.
  • Suitable meteorlogical conditions for spraying can be limited, especially for weed control over the summer fallow.

Double knockdown

'Double knock' refers to the sequential application of two weed control tactics applied in such a way that the second tactic controls any survivors of the first tactic. A common combination is glyphosate followed by paraquat or paraquat/diquat.

Benefits

  • Double knockdown delays or prevents the development of glyphosate resistance.
  • Using a double knockdown strategy reduces the number of (potentially resistant) weeds to be controlled in crop.
  • Excellent weed seedling control is achieved.

Issues

  • Glyphosate should be applied first, followed by paraquat or paraquat/diquat.
  • The timing between applications will vary depending on the main target weed species.
  • Consider the main target weed species when choosing what herbicides to use in the double knockdown.
  • Double knockdown is more expensive than a single herbicide application.
  • Seasonal conditions will influence the scale of on-farm implementation (as a double knockdown takes more time than a single application).

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