Amaranthus tuberculatus , commonly known as waterhemp, is an aggressive weed known to have resistance to multiple herbicide groups and it is of growing concern in Manitoba.
In June of 2025, Manitoba Agriculture announced a regulatory change to The Noxious Weeds Act and they have now downgraded Waterhemp from a Tier 1 to a Tier 2 noxious weed in certain Rural Municipalities (RMs) across the province.
Based on the current distribution and establishment of waterhemp and by consulting with industry associations, it was determined this change would aid in limiting the negative financial impact on producers whom otherwise would have lost extensive agricultural productivity in requiring the destruction of waterhemp on areas larger than 20 acres.
According to subsection 3(1) of The Noxious Weeds Act, if a weed is classified as Tier 2:
- Destruction is required for a weed colonization of less than 20 acres.
- If the area is more than 20 acres, the weed may be controlled rather than destroyed.
The updated classification enables the following municipalities to focus on containment and control rather than eradication:
Emerson – Franklin, Norfolk – Treherne, North Norfolk, Rhineland and WestLake – Gladstone, Brokenhead, Dauphin, De Salaberry, Dufferin, Ellice – Archie, Grey, Hanover, Lac du Bonnet, Macdonald, Montcalm, Morris, Piney, Reynolds, Ritchot, Roland, St. Andrews, Ste. Anne, St. Clements, Springfield, Stanley, Stuartburn, Tache and Whitemouth
For RMs not included in the above list, waterhemp still remains a Tier 1 weed, and that requires immediate action for removal when detected. That means:
Do not cut or put waterhemp plants through combine.
Pull or dig up waterhemp plants with roots intact and remove from field.
(Hand pulling and place in garbage bags)
Manitoba Agriculture has been actively engaged in educating producers and industry about waterhemp and other emerging weeds in the province. To support the recent reclassification of waterhemp, they will be launching a targeted educational campaign aimed at increasing awareness of waterhemp identification, its impact on crop production, and effective control methods.
This campaign will include:
- Updated fact sheets and identification guides
- Targeted outreach through extension channels
- Webinars and field demonstrations
- Collaboration with municipalities, agronomists, and producer organizations
If you have any questions about the regulatory changes or wish to collaborate on outreach initiatives, please contact provincial weeds specialist Kim Brown – Kim.Brown@gov.mb.ca