Common waterhemp, although relatively new to Ontario, has quickly shown itself to be a major concern for farmers. The weed was first confirmed in Ontario in a few small areas in 2002 and it has been spreading ever since. As waterhemp populations have grown across Ontario and Quebec, so has their resistance to certain herbicides. In fact, many waterhemp populations in Ontario have shown resistance to Groups 2-, 5- and 9- with some additionally resistant to post applied Group 14- herbicides.

Managing Waterhemp

Luckily, waterhemp is controllable in most crops with some planning and preparation. Generally, herbicides should provide 90% + control of weeds to help ensure reduced yield impact and seedbank return. 

James Ferrier, Technical Services Manager at Nufarm for Eastern Canada stresses the importance of planning when trying to reduce waterhemp seed return in Ontario and Quebec fields. “I know it’s cliché but one of the best ways to manage waterhemp is to try and get ahead of it, especially given the weeds’ high seed production and demonstrated ability to adapt quickly.”

Ferrier continues by adding that farmers should look at all aspects of their operation for controlling waterhemp. Rotate crops, look at herbicide application timing, and use a herbicide program that includes multiple effective modes of action. Fierce® EZ (Group 14-, Group 15-) is the best ranked product for controlling waterhemp. It can also be tank-mixed with BlackHawk® (Group 4-, Group 14-) and glyphosate for a pre-emergent herbicide application that delivers exceptional ease of use, enhanced burndown, and up to eight weeks of control of the toughest weeds.

Take a two-minute plot tour to watch Fierce EZ control glyphosate-resistant waterhemp in Southwestern Ontario.


  1. According to an article in Field Crop News citing University of Guelph research trials –