Control Tough Perennial & Annual Weeds With Pre Or Post Harvest

Every year brings its share of troublesome weeds, and the fall is the best time to control perennial and winter annual weeds.

There are 5 main benefits of a fall weed control program.

  1. Control of perennial weeds like Canada Thistle, quack grass and perennial sow thistle is best with a pre-harvest application when these weeds are actively growing and translocating nutrients to the roots. 
  2. As a pre-harvest aid to crop and weed dry down, improving harvest timing and grain sample quality. 
  3. Control of winter annuals including chickweed, stinkweed, narrow leaf hawk’s-beard with a later post-harvest application, as these weeds germinate long after harvest, and even after a frost. Fall is also the best time to control dandelions
  4. Reduce populations of troublesome weeds & crop volunteers. In the Prairies, over 60% of wild oats have group 1 resistance. Aid in controlling spread of weeds like water hemp, glyphosate resistant fleabane
  5. Control of winter annuals and perennials in the fall that can rob crops of valuable soil moisture in a dry spring

There are a number of great provincial resources for weed ID and control, including weedinfo.ca by the Ontario Weed Committee.

Before spraying, however, there are a couple of cautions that growers need to heed. Growers need to ensure that the pre-harvest product used is approved for their crop market. Pre-harvest crop timing is also important to avoid impacting yield and ensure there are no grain residues.  Growers also need to consider what crop will be planted next year, and if the herbicide they want to use could cause residue issue that could harm the crop. 

If you are unsure of the best course of action, contact your agronomist or provincial weed specialist.