Mixing Pre-Emergent & Knockdown Herbicides

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When applying pre-emergent herbicides, it is important to consider the incorporation restrictions of each and how they impact on mixtures with knockdown herbicides.

  • Trifluralin products must be incorporated within 4 hours. Glyphosate mixtures with Trifluralin should be avoided, as the short incorporation time does not allow sufficient Glyphosate uptake. Due to their speed of action, Gramoxone and Spray.Seed are more suited to mixtures with Trifluralin

  • Sakura and Boxer Gold need to be incorporated within 3 and 7 days respectively. Glyphosate mixtures with these products have a longer time in which to work, therefore will not be compromised to the same extent as Trifluralin tank mixes

  • Gramoxone and Spray.Seed are also compatible with Boxer Gold and Sakura, which provides an option to rotate herbicide groups for resistance management

  • Mixtures of either Gramoxone or Spray.Seed are not recommended with Rustler

  • Gramoxone and Spray.Seed will not control large tillered grass weeds. Both products should be used on small (1-3 leaf) weeds

  • Where Glyphosate has been applied recently to harder to control weeds such as Fleabane and Sow Thistle, a follow-up application of Gramoxone may provide an effective “Double Knock”.

Pre-emergent herbicides should ideally be applied to a moist seed bed prior to sowing. Although some products are more soluble than others and are claimed to wash off stubble, best results will be achieved when applied to bare soil. Any level of organic matter on the soil surface will reduce efficacy, however large spray droplets and higher water volumes can assist in getting the chemical onto the soil surface.

To avoid crop damage, physical separation of the seed from the applied chemical is required. The risk of crop damage is increased with:

  • Shallow sowing

  • Heavy rainfall after sowing

  • Varieties with a short coleoptile

  • Water logged soils

CroppingLiz KelleherRural Management Strategies