Tips for Cool Weather Spraying

In a long spring with periods of prolonged cool then flashes of hot weather, you could be combating advanced stage cool season weeds with outbursts of warm season weeds emerged as well. As seeding and spraying are colliding, here are a few tips to get the best performance out of your herbicides:

  • Spray when weeds are actively growing
  • Spray when the temperature is around maximum (15-25 0C) for the day
  • Apply herbicides when target weeds are most susceptible, timing is more important than application method
  • Use the water volume stated on the label
  • Use the surfactant or adjuvant included or recommended
  • Check the label and abide by rain free period
  • To improve control add at least one other tank mix partner for better results
  • Spray when wind is steady about 3–15 km/hr
  • Do not spray when temperature inversion conditions exist

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

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

Some of the herbicides that work well under relatively warmer conditions are:

  • Group 9 herbicide (e.g. Glyphosate)
  • Group 10 herbicides (e.g. Liberty (works better when it’s bright and sunny))
  • “Dim” group 1 herbicides (e.g. Select, Centurion)
  • Non-residual group 2 herbicides
  • Contact herbicides (e.g. Bromoxynil, Sencor, Basagran, Flexstar, Reflex, etc.)

What about morning dew? Dew may increase absorption and weed control by hydrating leaf cuticle, but may reduce weed control if there is too much and spray run-off occurs. If dewpoint is reached, it may be better to spray later in the morning and during day when the dew drying and leaf surface not so wet.

Frost? Do not spray if a frost is expected in the next 48-72 hours, also after frost has occurred, wait for 48-72 hours before resuming spraying.

Submitted by Nasir Shaikh, MAFRD Weeds Specialist

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