Giant Ragweed: Another Battle in the Field

In the last Agronomy Update, this series on herbicide-resistant weeds looked at waterhemp; now the conversation moves to giant ragweed.

"This herbicide-resistant weed is showing up in [our] area," according to Bob Marquette, Federated agronomist at the Albertville location, and "without proper management [giant ragweed] will find its way to other parts of Federated's trade area, if it already hasn't."

Giant ragweed resistance was first found with Group 2 herbicides (ALS-inhibitors) in the late 1990s in the "I" states (IL, IN, IA) and Ohio. "You probably know [Group 2] herbicides as Pursuit and Raptor," said Marquette.

"Resistance with giant ragweed is not new," he said, but "what is new is its resistance to Group 9 (glyphosate/Roundup®)." Resistance to what has become the go-to herbicide started showing up in the last few years, and is now confirmed in 11 states across the Midwest and southern U.S.

Resistance was built through repeated use of glyphosate year after year, first in soybeans and then in corn. "We found problem fields in both crops in Albertville this past growing season," said Marquette.

Giant ragweed is a "huge problem because of its competitiveness" and the fact that it produces a "massive number of seeds," Marquette noted. The battle with these weeds will intensify if growers don't take action. And the answer lies in modes of action.

As discussed in previous articles in this series, multiple, layered modes of action are being touted as the best option for achieving the desired level of weed control. And multiple, layered modes of action translates as "pre-emerge treatments followed by a solid early post-emerge program, and possibly a second post application," said Marquette.

"The new Roundup-Ready 2 Xtend® (dicamba) weed control system looks like it could be one piece of the puzzle" to get or keep control of giant ragweed, "but it needs to be used in conjunction with a good pre-emerge program to get the results we're after," he said, emphasizing that RR 2 Xtend is not a stand-alone product.

The battle rages with herbicide-resistant weeds. Talk to your Federated Agronomist to determine what products and programs should be in your weed-control arsenal.