COLUMBUS, Ohio -- Ohio crop growers are likely to find glyphosate-resistant marestail to be more abundant and harder to control this year thanks to the very wet fall and unseasonably warm weather we’ve had this winter, an Ohio State University Extension expert predicts.
But Ohio crop growers will find that a systems approach to marestail management using a combination of herbicide applications may just provide the most consistently effective control of and reduction in marestail population over time, said Mark Loux, an OSU Extension weed specialist.
Marestail is the most abundant herbicide-resistant weed growers have to grapple with in Ohio, he said. While traditionally found in the southwestern portions of Ohio, Loux said resistant populations of marestail are now found throughout the state.
And considering that essentially all of the marestail populations statewide are glyphosate-resistant, with 25 percent of the marestail population also resistant to ALS inhibitors, postemergence applications are often the least important in effective control, he said.
“The situation takes on even more significance this spring as crop growers were hampered from fall applications due to the lack of time and good weather last fall to get herbicide applied,” Loux said.
To deal with increasingly difficult weed control scenarios, he offers several approaches growers can take:
- Application of burndown plus residual herbicides in late March or early April, which allows applying early enough to ensure that burndown of emerged plants is not an issue.
- Application of burndown plus residual herbicides in late April or close to planting, which allows applying the residual later in the season and increases the potential for adequate control of late-emerging marestail plants. The disadvantage of waiting this late, especially as applications are delayed into May, is increased variability in the burndown of existing plants.
- Split the preplant application of herbicides with a late March or early April application of glyphosate plus 2,4-D plus a low rate of residual herbicide, followed by a second application at the time of soybean planting consisting of the majority of the residual herbicide plus whatever additional burndown is needed.
While there is no single perfect time for growers to apply herbicide in the spring, what is important is that they get rid of what marestail is present before soybeans emerge, and to also include herbicides that provide residual control because marestail will typically continue to emerge into June, Loux said.
“The bottom line here is that there is no one easy approach to marestail management that consistently optimizes both burndown and residual control of marestail,” he said. “Several possible approaches are offered for your consideration here, with the caveat that any of them may work in a field with a low infestation level and the growing season progresses normally.
“But the more complex approach will help ensure control when populations are higher and the growing season less favorable.”
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Photo credit: Kansas State University.