John Swanson, Federated agronomist at the Ogilvie location, recently attended a presentation by Kevin Bradley of the University of Missouri. Discussing modes (and/or sites) of action, Bradley tried "to help those of us in Minnesota and Wisconsin to avoid the situation . . . in Missouri," said Swanson. Herbicide resistant waterhemp and Palmer Amaranth are taking root in an extremely high percentage of their acres.

Bradly reported that Missouri growers are seeing resistance to two modes of action, and they have as high as five modes of resistance in one weed species. What can Minnesota growers learn from them? Swanson outlined several facts, based on Bradley's presentation.

• Continue -- or increase -- use of pre-emerge programs.
  • There is currently no resistance to Group 15 herbicides. Weeds that don't germinate and emerge are significantly less likely to become resistant to herbicides.
• Rotate modes of action, but more importantly, mix modes of action.
  • According to Bradley, using multiple modes of action in tank mixes during a single crop year has been more effective than merely rotating modes of action.
  • The more modes being applied, the better the chance of killing weeds and not allowing a resistant population to survive and/or explode.
• Layer residual products.
  • Missouri growers have found major success with residual products because hard-to-control weeds can germinate for long periods of time (the trait that makes them hard to control).
  • It is important to lay down a pre-emerge herbicide as part of a base program, but then add a residual product with a post application "to continue to help prevent these weeds from germinating later in the season, when we can't go back and spray," said Swanson (Dual® is a good example).

"We have some very hard-to-control and resistant weeds coming our way," said Swanson, "and we need to learn from others and not make the same mistakes they did." Following these basic guidelines will set Minnesota and Wisconsin growers on the right path.

Contact your Federated Agronomist to further discuss modes of action and application programs for 2017.

*See this link for a more complete discussion of the terms, as defined by Dr. Joe Armstrong of the University of Oklahoma Cooperative Extension Service.