By Harold Watters, CCA, Ohio State University Extension agronomist
We are just compiling the Extension fall soybean weed surveys; it is bad again with waterhemp, giant ragweed, and marestail leading — this is the first year that we have a pigweed species in the number one spot in several counties. The number of clean fields has gone down, likely due to late planting and then missing the timing on weed size.
I spoke with Mark Loux last week and shared preliminary results of the survey. His response was that we have good technology for dealing with all of these weeds —RRXtend, LibertyLink and now Enlist. But timing was critical this year and we just couldn’t hit it with the weather. So speak now with your seed supplier, and your herbicide supplier. Plan to use a different program than you used last year. Add pre-emergent herbicides at planting or with that burndown the week before planting. And in waterhemp areas (there are lots of them) add an additional pre-emergent herbicide at post application timing to extend your residual program. Good products are Zidua, Warrant, even Dual.
Lastly as I say above, fall herbicides do work. This can be an excellent start to your marestail management program. This year we let our marestail get too big and they were difficult to take down even with our best Extend, Liberty or Enlist program.
How late in the year can we spray? I have sprayed in December, just before a big freeze and still had success. One year — the winter with no winter — I sprayed in February.