
5 things to know to keep this herbicide-resistant weed out of your fields
Because it has adapted to repeated applications of various herbicides, giant ragweed’s effect on soybean crops cannot be understated.
“Managing for herbicide-resistant giant ragweed is truly a matter of planning and preparation,” says Bill Johnson, Ph.D., professor of weed science at Purdue University. “Failure to do so can lead to crop yield losses up to 90 percent.”
In a recent Focus on Soybean webcast on the Plant Management Network, Johnson recommended strategies for combating giant ragweed.
“Putting the post-emergence treatments on in a timely manner is really important. We cannot let these plants get big or we increase the risk of failure to control them,” he says. “We want to scout our fields late in the year to see how well our control tactics are working. This is going to be the best way for us to determine whether or not we have a resistance problem that is developing and if our current strategies are effective.”
Johnson says farmers should remember these five key takeaways to manage giant ragweed:
1. Giant ragweed germinates early.
It can outgrow and outcompete your soybeans for sunlight, moisture and nutrients. Crop yield losses of 30-90 percent have been documented.
2. Giant ragweed is becoming resistant to more herbicides over time.
It is important to determine if the ragweed you are treating is resistant to Group 2 (ALS inhibitors like FirstRate, Classic®, or Scepter), Group 9 (glyphosate) or both types of herbicides. When using the appropriate herbicide, make sure to apply the product as labeled to reduce the chance of creating more herbicide-resistant plants.