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Cool growing conditions have limited the amount of weed growth in fields this spring. These cool conditions can also affect herbicide performance. Formulation and target weeds must be considered when deciding on the time required between application and disturbance from tillage or seeding. Remember that glyphosate is a systemic herbicide that needs time to work for maximum control. Additionally, with temperatures getting close to or dipping slightly below zero at night in many areas, it is recommended to only spray glyphosate after temperatures have warmed the following day. A hard frost will require a longer recovery time as plants must be assessed for new growth before applying the herbicide. Weeds must be actively growing to ensure herbicide uptake and maximum kill.
Cleanstart contains a contact herbicide in addition to glyphosate to provide control of glyphosate-tolerant volunteers. Contact herbicides work best under warm growing conditions and when weeds are small (1-to 3- leaf stage). So when conditions are cool, should you wait and spray larger weeds? Timing is more critical than temperature. Weed burnoff should continue even though growth is slow. Coverage is very important with contact herbicides. Research at AAFC suggests that efficacy of Cleanstart drops dramatically as spray quality (droplet size) increases and carrier volume decreases so consider a combination of at least a medium spray quality with a minimum water volume of 7 gpa when using Cleanstart as a burnoff.
Remember that no other tank mixes are registered for volunteer canola control ahead of canola. Phenoxy herbicides (2,4-D and MCPA) can leave a residue for as long as three weeks in the soil and must not be used prior to seeding canola. Don’t jeopardize your seed investment by sabotaging emergence with herbicide residues. Always read and follow product labels before application.