As you are well aware, most marestail is now resistant to glyphosate! So don’t spray glyphosate alone and expect good control. Also, don’t allow marestail to get too large and expect good control! It was close to 80 degrees this weekend, there’s ample soil moisture and marestail is starting to grow!
That is a 3.5″ knife and the marestail pictured above is just as big as the knife! And that picture was taken this weekend, not more than 50′ from my office! It won’t be long at all before that plant starts to come up off the ground and it will be 4-6″ tall before you know it. Marestail becomes much harder to control when it gets about 6″ tall.
So what will kill that thing today? 2,4-D, Sharpen, or Elevore added to glyphosate or paraquat will do a pretty good job if burndown alone is your goal. Paraquat or Liberty alone will do the job. If you are also looking for a residual herbicide to help prevent a spring flush, you can add saflufenacil or atrazine or labeled atrazine or saflufenacil containing materials for corn acres. For soybean acres, glyphosate plus 2,4-D with the addition of metribuzin, saflufenacil, or cloransulam, chlorimuron, or soybean products containing any of these materials should give good control.
Wet weather could make timely planting difficult, dousing fields now allows you to get into the field sooner when planting windows are short.
If you are utilizing a cover crop and you have good cover, you might find that marestail is quite a bit smaller due to the competition from the cover crop – another good reason to consider a cover crop!
Good luck in 2020! Remember, weeds are highly competitive with corn! Some believe that weeds germinating next to germinating corn can cause yield loss even before the corn emerges. Mind your weed sizes carefully to get all the yield possible!