By Harold Watters, Ohio State University Extension agronomist
Is it too late to make a fall application for marestail control? Probably not, but will the conditions allow? That is another story. I have seen a few folks squeeze in fall applications, and heard several who said they will still try. I made a couple of applications last fall in mid-December and surprisingly they worked. I used glyphosate and 2,4-D. It went under snow shortly after and then deep cold, so I wasn’t sure if I had wasted my time. But when we started to green up in the spring, it was mostly dead — not perfect but pretty good. This year we had a long fall, and plenty of moisture to get weeds started. It’s green out there under those corn stalks.
We have published this information fairly frequently in the C.O.R.N. newsletter (http://corn.osu.edu), and our suggestions for fall treatments have not really changed much. Herbicides are applied in the fall primarily for control of an existing infestation of winter annuals, volunteer wheat, biennials (wild carrot, poison hemlock), or cool-season perennials (dandelion, quackgrass, Canada thistle) that are most susceptible to herbicides in the fall. We have already been asked a number of times how late in the fall herbicides can be applied and still be effective. In Mark Loux’s research, herbicides seem to be effective for control of winter annuals and biennials well into December. The rate of plant death can slow considerably, but this is not a problem since weeds just have to die by early spring. Control of perennials typically declines in late November or early December though, depending upon weather.
We consider the fall herbicide application to be an essential component of an effective Marestail management program, although fall is not where the majority of the money should be spent on managing this weed. Even where the herbicides lack residual, the fall treatment seems to enable more effective control of Marestail the following season.
There is a core group of herbicide treatments that make sense to use in the fall based on their effectiveness and cost, as follows. On biology and control of marestail look over Mark’s website: https://u.osu.edu/osuweeds/, and see the control factsheet.
- Glyphosate + 2,4-D – can be used in the fall prior to any spring crop. It is the most effective of the treatments shown here on grasses, biennials, and perennials.
- 2,4-D + dicamba (premixes = Weedmaster, Brash, etc) — can be used prior to corn or soybeans. This combination controls most broadleaf weeds, but is not as effective as glyphosate-based treatments on dandelion or Canada thistle.
- Canopy EX or DF (or the generics) + 2,4-D — can be used prior to soybeans. The only one of the treatments listed here that provides residual control into the following spring/early summer.