Pulse School: Herbicide Layering — The Tag Team Approach to Fighting Weeds and Resistance

“Herbicide layering” looks to be an effective approach to managing hard-to-control cleavers in pulses.

As Eric Johnson, weed scientist at the University of Saskatchewan, explains in this Pulse School episode, herbicide layering is the application of different modes of action sequentially. It usually involves a pre-seed soil-applied herbicide, such as sulfentrazone, ethalflurolin or pyroxasulfone, , followed by a post-emergence herbicide with a different chemistry.

“We’re trying to use multiple modes of action in the same year, because we know (it’s) one of the best ways to delay the onset of herbicide resistance,” he notes.

Much of the early work Johnson is involved in has focused on controlling group 2 resistant cleavers in peas on soils with high organic matter. As he explains, they’ve found the two applications complement each other in instances where a pre- or post- application by itself is inadequate.

Johnson says they found pre-seed herbicides controlled 40-60 percent of targeted weeds. Control from the in-crop application was in the 50 to a 80 percent range.

“When we combined the two together, we were usually over the 80 percent of control. It improved consistency of control and the overall efficacy,” he explains.

One area he says that requires further study is whether the pre-seed herbicide could predispose a marginally-tolerant crop to herbicide injury from the post-emergence application.

Related: Pulse School: A Long-Term Plan for the Control of Cleavers

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