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Mixing Pre-Emergent & Knockdown Herbicides

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 in the same way 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.
  • 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, a follow up application of Gramoxone may provide an effective “Double Knock”. This will be more effective if the Glyphosate was part of a tank mix with a phenoxy herbicide.

Pre-emergent herbicides should 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 ground. Any level of organic matter on the soil surface will reduce efficacy.

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