Getting What You Expect Out of Your Herbicide – Part 1: Cold Spring Weather

Submitted by Anastasia Kubinec, MAFRD Oilseed Crop Specialist

As seeding and spraying collide, for pre-seed burn off and winter cereals in-crop applications, here are some tips for early applications to get the best performance out of your herbicides. Part 1 is only covering the pre-seed herbicide options and the types of products that would be used on winter cereals.

  • Spray when weeds are actively growing
  • Spray when the temperatures are at least 150C
  • Use the water volume stated on the label
  • Use the surfactant or adjuvant included or recommended
  • Watch and follow the rain free period

Some of the herbicides that work well under cool conditions are:

  • Most Group 4 herbicides
  • Most of the residual herbicides of any group
  • “Fop” group 1 herbicides (ex. Horizon)
  • Carfentrazone (ex. CleanStart, Aim)

Frost and Spraying

Actual temperature and duration of the frost will impact plant growth, how well the herbicide will work and crop safety. For most Group 1 and Group 2 herbicides, it is better to wait at least 48 hours before application to allow weeds and the crop to recoup and start actively growing.

For pre-seed glyphosate, after a light frost (0 to -2°C), spraying could resume 24 hours later, but temperatures need to go up. Avoid spraying until the temperature is above 8°C….the closer it is to 150C and above, the better the control. If a harder frost occurs, avoid spraying for 48 hours and assess the damage on the target weeds. You want to see that plants are still green and actively growing, and daytime temperatures are warming up.

Frost occurring within 24 hours after spraying can also impact control.

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