Herbicide Application in Dry Weather – Rules of Thumb

See Dry Weather Weed Control on Manitoba Agriculture website for more details and complete recommendations and cautions.

Dry weather means both weeds and crops shift gears. Weed spectrums can be different,  post-emergent herbicides can  be less effective because weeds may have smaller leaves and/or thicker cuticles (waxy layer) that slows the penetration of herbicides.

Some herbicides withstand dry weather better than others so choose your product carefully. Here are some general guidelines on weed control during a dry period.

1. Remove weeds early.

2. Know your crop stage.

3.  Review the “Effects of Growing Conditions” section of each product in the Manitoba Agriculture Guide to Field Crop Protection to determine likely outcomes.

4. High Daytime temperatures can trigger crop injury in some herbicides.

5. Use full rates of herbicide.

6. Use higher water volumes.

7. Use split applications of broadleaf and grassy herbicides rather than tank mixing if the Guide to Field Crop Protection warns that antagonism can occur.

8. Check the forecast for rain – shallow, stressed crops roots may be impacted by herbicides moving into the root zone.

9. Compare the risk of crop injury to the risk of yield loss due to weed pressure.

 

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Can Sidebanded Nitrogen Cause Injury in a Dry Year?

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist

With a lack of seedbed moisture, there are justified concerns about seedplaced fertilizer injury to canola and other crops.  How safe is sidebanded nitrogen? Research studies by  Dr. Cindy Grant documented considerable canola stand thinning when high rates of sidebanded urea or UAN solution were applied.  Agrotain (AT) served to reduce stand injury, but is no longer supported for this use by the manufacturer. 

Points:
  • Stands were thinned at even modest N rates, on a clay loam soil.  At high rates stands were reduced to 50%
  • Crop growth compensated for reduced stands and generally produced as good a yield as the Agrotain protected stands, except at the highest rate.
For more detailed analysis and discussion on the issue see the full .pdf
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
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