Most of us have marestail across Ohio. And pretty much all of us have resistant marestail, likely resistant to glyphosate and also likely resistant to the ALS herbicides. And if we all switch to Xtend beans then it will likely also soon be resistant to dicamba. Uh-oh, this is starting to sound bad for the future of soybean weed control.
Table 1. The table below shows the number of fields observed in the Ohio Fall Soybean Weed Survey by region, the percent of fields without weeds and weeds observed ranked by appearance.
|Region of Ohio|
Number of fields observed
% of fields without weeds
Appearance by weed; ranked in order
Marestail; grasses; Common lambsquarters; Volunteer corn; and pigweeds
Marestail; Giant ragweed; Common ragweed; and Redroot pigweed
Giant ragweed; Marestail
Marestail; Giant ragweed; Common ragweed; grasses; pigweeds
Giant ragweed; Marestail; Tall waterhemp; Volunteer corn; grasses
Marestail; Giant ragweed; Volunteer corn; common ragweed; pigweeds
I take this information below from an article by Mark Loux, from October 2011 regarding Fall Herbicide Treatments. Guess what, it’s the same situation we are in today. Remember fall 2011 — wet with delayed harvest.
We have published this same type of information fairly frequently in C.O.R.N. (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 or marestail, 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 our 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.