If your time it right, a post-harvest herbicide application can be an excellent way to set up your field for seeding next spring. The idea is to control emerging winter annuals, such as hawk’s beard and shepherd’s purse as well as perennial weeds such as dandelions and Canadian thistle in crops that you’ve swathed.
Going in with a post-harvest herbicide application also helps you control and clean up weeds that you may not have been able to hit pre-harvest due to the thick and tall crop canopy.
So, what’s the key to getting most out of your post-herbicide application? Pay attention to your temperature, timing and weed emergence. After you’ve swathed or harvested, look for new leaves to signal a good amount of weed regrowth, and give you a target to hit with your herbicide.
Keep an eye on the temperature, too. If you’ve had a frost, those emerging weeds can shut themselves down and not show any growth activity.
That’s why it’s best to wait a few hours for your field to warm up after a light frost — or two to three days when you’ve had a heavy frost — to ensure those weeds are growing again and that you’ll get the best possible herbicide coverage.
This agronomy tip is brought to you by David Forster, agronomic service representative, Saskatchewan North, with Syngenta Canada Inc.