Herbicide resistance

As of December 2021, there are 162 confirmed cases of resistance across all pigweed species, herbicides, and states in the US. Forty of these reports detail resistances to multiple herbicide groups within a single plant population.

What is Herbicide Resistance?

Herbicide resistance is the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal. Think of it this way: 

We used to be able to kill this plant with this herbicide... Now we can't!

Herbicide resistance develops when the same herbicide or herbicide groups are used, repeatedly, over space and time. The genes that confer herbicide resistance are already present in a field when herbicides are applied. Susceptible plants are killed while resistant plants continue to grow and set seed. Over time, seed produced by resistant plants dominate the seedbank.

How to recognize herbicide resistance on your farm

Ask yourself if you have done everything right (i.e. right herbicide at the right rate against the right species, sprayer calibrated properly, appropriate adjuvants used, etc.) Then look to see if you have dead plants intermixed with live plants of the same species (that were treated at the same time) and a problem with an uncontrolled species that is growing with time. If you can’t rule out human error, adverse weather events that reduced herbicide performance, and equipment malfunction, there's a good chance you have herbicide-resistant weeds.

Get in touch with your cooperative extension personnel about next steps/best management practices.