Ohio grain farmers are likely to find more glyphosate-resistant marestail in their fields this year because of the wet fall and warm winter, says an Ohio State University Extension weed specialist.
Marestail is the most abundant, herbicide-resistant weed Ohio growers deal with, and according to Mark Loux, a combination of herbicide applications can provide the most consistent, effective control.
Resistant populations were traditionally found in southwestern Ohio, but now essentially all of the marestail statewide is glyphosate-resistant. Twenty-five percent of marestail also is resistant to ALS inhibitors, meaning postemergence herbicide applications are often the least effective, Loux 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,” he said.
Loux offers several approaches growers can take to deal with increasingly difficult weed control scenarios:
- Apply burndown plus residual herbicides in late March or early April, which is applying early enough that burndown of emerged crops is not an issue.
- Apply burndown plus residual herbicides in late April or close to planting, which 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 crops.
- Split the pre-plant application of herbicides with a late March or early April application of glyphosate plus 2,4-D plus a low rate of residual herbicide. Follow that with a second application. at the time of planting. that consists of the majority of the residual herbicide plus whatever additional burndown is needed.
While there is no perfect time for growers to apply herbicide in the spring, what is important is that they get rid of what marestail is present before crops emerge. It’s also important to include herbicides that provide residual control because marestail will typically continue to emerge into June.
“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.”