Submitted by Jeanette Gaultier, MAFRI Pesticide Specialist

We cautioned last week about herbicide application in cool temperatures. Since the 2013 growing season has not been setting records for heat, you may be stuck trying to balance optimal temperatures with recommended herbicide application timings. 

Crop injury in some situations may be unavoidable since both temperature and incorrect crop staging affect crop tolerance to herbicides.  The good news is that you may not need to be concerned if you see symptoms in your crop post application since not all injury contributes to yield loss.  

  • Growth Setback – Stunting of cereal crops treated with certain group 2 herbicides (e.g. Everest, Simplicity) or with Avenge is possible but generally will not affect yield.  Improper timing or cool temperatures during group 1 herbicide application can also cause setback.  Do not worry about yield penalties though, unless stunting is severe or other growth setbacks, such as reduced tillering or stem/head kinking, are present.
  • Chlorosis –Pale plants and chlorosis are indicators of reduced photosynthesis, a process necessary for crop growth.  However, slight chlorosis of leaves and growing points will not lead to decreased yields if plants are able to ‘grow out’ of the stress early in the season.  For example, beans treated with Basagran + group 1 herbicide may have both green and yellow leaves on the same plant without affecting growth.  Cool temperature application of group 2 herbicides and/or glyphosate may also cause slight chlorosis, that crops can grow out, depending on the severity.  Do not worry unless symptoms are severe; plants are more chlorotic than not or deformed growth tips, necrosis are also present.

The above are generalizations and yield penalties from herbicide injury in specific crop situations can vary depending on the severity of injury symptoms, crop growth stage as well as other factors that may be contributing to crop stress.

If you are concerned about your crop or want a second opinion, crop samples can be submitted to your local GO office or the Crop Diagnostic Centre.  MAFRI staff are able to provide visual assessment of crop injury only; you may be referred to a private lab for herbicide residue or nutrient testing if assessment of the symptoms is inconclusive. 





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