Hi, my name's Mark Renz, an Extension weed specialist with the University of
Wisconsin-Madison and Cooperative Extension. And I'm here today to talk to
you about pigweed identification. Pigweeds have long been common to the
Midwest and Wisconsin. What we have that's new is we have a couple species
that are rapidly spreading and becoming more established. In particular we have
tall, or common waterhemp, which I'm going to refer to as waterhemp in the future,
and Palmer Amaranth. Why should we be concerned about identifying these
species over other pigweeds? Well, their biology is a little bit
different. First off they're much more competitive than other pigweeds. They
produce more seeds and can germinate and emerge much later into the growing
season. And secondarily, their ability to evolve resistance to many of our
herbicides is much more common than these others. Therefore we're really
interested in identifying these populations and trying to manage them
early and prevent them from spreading. So how do we identify them? We're going to
focus on vegetative characteristics because that's really the time when we
need to identify them so we can invoke management before seed production.
There's really a two-step process; it's pretty easy to help identify them. The
first step that we want to look at is looking at the stems. So if we want to
look at a pigweed here, we want to look right around in the middle of the plant
and focus in and look really closely at that stem. What you'll see what that stem
is it's got a lot of very fine small hairs, it almost look like a slight fuzz.
That's a really good indicator of red root pigweed. Now
Smooth pigweed is another common species we have, that also will have
hairs. But it's not nearly as fuzzy as we see with the redroot pigweed. Those
are two of our more common species. If that stem is not hairy and is absent of
hairs, it's either Palmer Amaranth Waterhemp. Or it could be
spiny amaranth. This plant is also present in Wisconsin,
but this one is easily distinguished because if you look where the leaf
attaches to the stem, you'll see a distinct spine there. All you got to do
is pull this plant and you'll know that it's there and probably never touch it
again because the sharpness. Okay so step one is to
look at that stem. Now if we know that it's smooth and we know it doesn't have
or lacks hairs and we know that doesn't have a spine it's either waterhemp or
Palmar. What's the next step is we want to compare the petiole length. What's a
petiole? It's where the leaf blade attaches to the stem with that stuff,
that's what we call a petiole. We want to compare the length of that petiole to the
length of the leaf blade. If it's longer than the leaf blade, that's Palmer
Amaranth, whereas if that petiole that we see here is shorter than the leaf blade,
that's waterhemp that you're dealing with, the really nice characteristic that
we can use to identify it. There's a range of other characteristics such as
leaf shape that are different. There's lots of other resources available that
can talk about this, but this two-step process of first looking for the stems,
seeing if those stems have hairs or not. If they don't have hairs it's one of
three species Palmer Amaranth, waterhemp, or spiny amaranth, and then looking for
those spines present. If it lacks spines then it's then it's either waterhemp or
Palmer then looking at the length of that petiole. Those are two really good
characteristics to differentiate these species. So now that you know how to
differentiate between these pigweed species, we're asking for some help. We'd
like to have you report present locations of either Palmer Amaranth or
waterhemp because these aren't widespread
in Wisconsin. How can we do this? Well we have several different options.
The first option would be to contact someone in extension like a County agent.
The second option would be to use a free app called the Great Lakes Early
Detection Network. Please look at the URL in this video for information on how to
download and use that app for free, or the third option is to simply email us
at reportapigweed@gmail.com. Now in any of these instances we're going to
ask for some key information. The first piece of information we're going to ask
for is the location, either an address or GPS coordinates. Second piece of
information we're going to ask for is what type of habitat this plant was
found in like a cornfield or soybean field, and then the third piece of
information we're going to ask for some close-up pictures that allow us to
confirm the identification of these species using the traits that we've just
discussed. If you're concerned about herbicide resistance, you can feel free
to add that into your report as well. This will really help us in
understanding where these populations are in Wisconsin and to help with some
coordinated efforts to limit the spread of these and potentially eradicate some
of these species in local situations where possible. Thanks for your help, and
have a great day.