Soybean weed scouting: Control of volunteer corn

Soybean weed scouting: Control of volunteer corn


Hello, I’m Vince Davis. I’m the cropping system’s Extension weed
science specialist at the University of Wisconsin–Madison. Today, it’s late August and I’m standing
in a field of soybeans with severe infestations of volunteer corn. Glyphosate resistant volunteer corn in soybeans
is a problem for several different reasons. It’s not a weed problem that has evolved
into high density or problematic situations that’s difficult to control in the long
term, but in the short term, one–it reduces our yield in that current year, two–if these
plants get large enough to actually produce kernels, it can reduce the quality of our
soybean grain at harvest time, three–it can be a little bit more problematic at harvest
time, unless you’re harvesting after a frost, and four–probably the biggest thing is that
it’s completely unsightly to be looking at as you drive down the road. And I would say it’s one of our most prevalent
weeds, I don’t know if it’s the most problematic, but it’s one of our most prevalent weeds
in Wisconsin right now. The fifth issue with volunteer, Roundup ready
corn and our soybean is an issue that the impacts are a little less known, but it is
somewhat scary, and that is many of these volunteer corn plants also express low levels
of the BT toxin because so many of our corn hybrids are stacked with both glyphosate resistant
and BT resistant technologies. And so, it’s questionable as to what those
low levels of BT toxins in these plants do from a western corn rootworm management strategy,
and there’s been some research work recently published over the last couple of years, primarily
coming out of Purdue that faces that issue that you can read up on. So, some reasons we are concerned and that
we should be looking to control this particular weed. Now the good news with volunteer corn is this
is not a difficult weed to control, when we go out with our postemergence glyphosate,
there’s two strategies you can use, really the one and only strategy I guess is to use
a postemergence grass herbicide, or what we call an ACC, ace, inhibitor herbicide that
attacks primarily grasses. There’s two families of those herbicides
that we call the fops and the dims, some popular ones are quizalofop, and on the dims side,
one of our most popular ones are clethodim products and a number of generic clethodim
products. Sethoxydim is another product, of all the
herbicides sethoxydim is probably one of the more weaker volunteer corn herbicides, but
it can get the job done if it’s priced right. But most notably is clethodim products to
use in these situations. The two strategies when you add those products
in is when you go out early in your first postemergence application timing with that
grass herbicide, or wait til later because emergence can be a little bit later in some
of the clumps of kernels, the ears that get left behind. I’m not sure of those two strategies which
is better. I tend to think probably going out earlier,
the most important thing is that you’re just scouting ahead of those postemergence
application and determining what your volunteer corn density is. It seems to be real easy at that postemergence
timing to go out and scout and not think you have very many volunteer corn plants out there
because they just don’t seem all that numerous until the soybeans get large and you’re
standing at this time of the year when it’s really easy to see these weed escapes. As we’re standing in this density right
here, we could be looking at 25-30 percent yield loss from this density of volunteer
corn right here. As we move over into this area over here,
here’s an area across this strip here, here’s an area where we did spray clethodim or a
grass herbicide at that postemergence glyphosate timing. It was kind of early, the volunteer corn was
all in the 6-12 inch range. It was a fairly low rate for control, and
you can see we didn’t get perfect control out here, but probably enough control that
we salvaged our yield to acceptable levels. So again, it’s not a difficult weed to control,
but it is a weed that is much more unsightly late in the year than early in the year. So keep that in mind when you’re out there
scouting and trying to determine whether you want to spend those additional few bucks to
pick up this volunteer corn for a variety of the reasons I just discussed.