Hello folks. This is Rodrigo Werley; I'm the new extension cropping systems
weed scientist with UW Madison and UW Extension. Today I'm here to provide you
with some tips for waterhemp management in soybeans for the 2018 growing season.
Earlier this year in January, during the agronomy update meetings, I conducted a
survey and I asked farmers, agronomists, and industry reps,
"What were the most concerning weeds in the state of Wisconsin?" Waterhemp was
the number one concerning species. That was followed by giant ragweed. This is
why today I want to focus a little bit in waterhemp management. Before we
talk about waterhemp management I just want to share this with you
this map. In red here you have the counties where glyphosate resistant
waterhemp populations have been confirmed in the state of Wisconsin. As
you can see here we have 25 counties with glyphosate resistant waterhemp
populations. We also have four counties with confirmed PPO resistant populations.
Those counties are Iowa, Monroe, Pierce, and San Croix County. So, glyphosate
resistance and also some instances of PPO resistance confirmed in the state
and that difficult, that makes, you know, control of this species more challenging.
Before we start talking about management of water hemp here, I just want to
talk a little bit about the biology. If you're not familiar with the water hemp
plant, this is what a water hemp young plant looks like. You have this
long, narrow leaves in there. They tend to be waxy and this light green coloration.
In order to differentiate water hemp from some of the other pig weed species,
you want to look at that stem there. Water hemp stems won't have those white,
short hairs that you see in red root pigweed. And the petiole here, which is the
structure that connects the leaf blade to the stem, is short there. Okay, so no hair
and short petiole, you know, long and narrow leaves, those are key identifying
characteristics for waterhemp. In order to manage a weed species, it's
important to understand its biology and I classify waterhemp as this ideal weed
for cropping systems. The reason being is because the genetically diverse species
is how it has male and female plants. Okay,
the female plants are very prolific seed producers and the male plants are very
prolific pollen producers. Okay, and this species, you know, this male and female plants,
the out cross and there's a lot of opportunities there for genetic
diversity for this out crossing species, and when you have genetic diverse weed
population out there, you're more likely to select for resistant biotypes
if you're using the same management strategy over and over. Waterhemp is a
little different from some of the other weed species we deal with. The
reason being is that because it has a wide emergence window. So water hemp starts
emerging a little later in the season, so we'll start emerging in May and will
continue to emerge all the way through July or even August sometimes, and that's
why it's right you take an approach, a one-pass approach, for control of
waterhemp may not provide adequate level of weed control there. It has vigorous
growth, so once conditions are ideal, if you have warm water and enough soil
moisture, this plant can put more than an inch a day. And the reason why that becomes
important, is that if you have glyphosate resistant waterhemp and you're trying to
control this weed with a post emergence application of a compact product, such as
your PPOs or even glyphosate and Liberty link soybeans, you gotta be there
early because if you miss that ideal window, that weed is gonna get too
big and you're not likely to get good levels of weed control. This weed
species is very well adapted to minimum to no tillage. It produces very small
seeds and when you have you minimum or no-tillage out there, you
provide this weed the ideal condition or environment if you would to get
established. So all combined, how these factors
combine, you know, they make water hemp this what I call ideal weed for current
systems there. So what about management? First of all, I want to share some of
this data here from, you know, USDA national AG statistic service. This figure here on
the left is the herbicide use pattern in soybeans for the 2015 year
and as you can see here, the primary herbicides that we're using the
most are glyphosate and imazethapyte, okay, and on the right side of the
screen here, I have the results of my survey again where I asked the various
groups of AG professionals out there, "What is the standard herbicide program
for weed control in soybeans, whether it's a one pass program or whether is a
two pass program in season?" And as you can see here, roughly 45% of our farmers and
agronomists are, you know, adopting-still adopting-a one pass program in soybeans.
They're combining with this USDA data here. You can see that herbicide is
mainly going to be glyphosate with or without imazethpyre. Okay, so if you
have a weed that emerges year-round and has evolved resistance to glyphosate
using life as it alone or using the one pass with glyphosate + imazethapyre,
will probably not help you achieve the level of weed control you want to
achieve with it. The one thing I want to stress out, if you look at this figure
here, we're not taking advantage or we're not incorporating pre-emergent
herbicides, you know, herbicide programs and soybean as often as we could and
that's something we should be looking into as we go into the 2018 growing
season, particularly if you are struggling with some of this troublesome
weeds that I'm talking about. So those are some pictures that I obtained from
my colleague down in Nebraska Dr. Amit Jhala. It;s some studies that we ran a
couple of years ago. Look, you know, different herbicide programs and the
control of glyphosate resistant waterhemp in a Liberty link system. So
here I have an untreated control plot, just so you have a feeling on how bad
the pressure there was. Here is a treatment on the right top corner here
where we use the post program only. Okay, and as you can see here, we probably came
in a little late with that application, you know, so we miss that ideal window. So,
you see some of regrowth there of those plants, but the other point there is that a
lot of yield potential went away already just because of that early season
competition. Okay, these bottom two pictures here is where we have a solid
pre-emergent herbicide that was put down at planting and then you can see the
huge difference there in terms of weed control. Okay, a very good level of weed
control where a good pre-emergent herbicide was put at planting. Okay, the
other thing I want to comment here as farmers are selecting their pre-emergent
herbicides for the 2018 growing season,
research has shown that using a pre-emergent herbicide with two
effective sites of action tend to provide better level of weed control.
Okay, and in this figure, here, these treatments that I'm showing here contain
two effective modes of action. For instance, the picture in the left
here in the bottom has a group 15 plus a group 14 and then the picture on the
bottom right here has got a herbicide that contains actually three active
ingredients - 2 from group 2 are an ALS herbicides plus a group 14. So in terms
of recommendation, you know, as we go into the 2018 growing season, we gotta start
clean. If you are in a system where tillage is part of your operation, you
know, a pre-planned tillage will assist eliminating any established weeds. If
you're in a no-till system or if you're not going to be doing any pre-plant
tillage and you have established weeds, you want to make sure you use an effective
burn down and there are several effective burn downs out there that can
be used at that point. I also encourage, you know, at that planting time when you
go out with a burn down, put a good pre-emergence program and
again look for herbicides that contain multiple effective modes of action. You
can make your own premixes, for instance, you can buy a metribuzine product, you
can buy an acetochlor product, mix then spray it, or you can go out there
and buy the premixes. Okay, so that's the way you start it; that will
help you start clean. Three to four weeks into your growing season you know start
scouting your fields and as those weeds start breaking through the ground
there because the residual is fading away, that's the time you want to be out
there with the post emergence. You don't want to let those weeds grow too much. So,
when you're selecting your post emergence herbicide program, you gotta
understand what type of resistant weeds you are dealing with because if you have
glyphosate resistant weeds there, glyphosate won't be a good strategy. So
you got to be mixing the glyphosate with something else. Okay,
you can use your group 14 herbicides. If you're in a Liberty link system, you can
use glufosinate post emergence. However, I urge you if you're gonna use glofosinate,
you gotta spray the weeds when they are small. Glofsinate is a contact
product so you got to be there at the right time when you're 4 inches or
smaller. And if you're in the round up, ready to extend soybean system, dicamba
becomes an option. If you're gonna be using dicamba post emergence, I
recommend you to use it early in the season and be mindful with sensitive crops
around you when going that route. The other thing I want to talk
about, when you come with your post program, you have your post emergence
products, if your crop is still a long ways from closing the canopy, you may
want to consider including a group 15 herbicide if you would so your sudichlors,
metolachors and so on because what those you know adding those
at that time will provide an extended residual control until your crop will
close that canopy there. If you're not familiar with the modes of action that
are within the products you're going to be using, if you have some questions, you
can always go and check the NPM Wisconsin herbicide mode of action
chart. You can just go to the internet and download
the PDF that we have available. In this PDF there we provide information for all
the herbicides that are labeled in the state of Wisconsin. So you can check the
herbicide product and then you go to the side of action column there and you can
see how many effective sites of action are within each one of those products. So
it's a great resource to have as you are selecting your herbicides for 2018
growing season. So just to wrap things up here, if you're struggling with waterhemp
two-pass program, it's probably the way to go. You want to put a good
pre-emergent herbicide down there with two effective modes of action. You want
to continuously scout your field and when you start seeing the weeds, you want
to put your post program and depending how far you are for your crop to
close canopy, you may want to add a residual product or a group 15 herbicide
with your post program. You know, to obtain a better level of weed control.
You want to take advantage of known chemical strategies as often as possibl.,
Managing herbicide resistant weeds with herbicides alone will not be a
sustainable strategy, especially because the number of effective options and the
tool blocks are getting very limited. Okay, so take advantage of non-chemical
strategy tillage if that fits your operation into row cultivation you know.
Go narrow on your soybeans there because that's going to lead to early canopy
closure and better weed suppression. Cover crops might be a helpful tool
there as well. So you know think outside to jug a little bit as often as you can
and I actually would say: minimize seed dispersal so if you have a field that has
troublesome weeds, you know, make sure you harvest that field last and when
you're moving that equipment around, make sure that equipment gets clean so you
are not spreading the problem within your operation. And take advantage of
rotational years where more herbicide options are available, so if you have
water hemp and you're going into a corn year,
there are several herbicides that are very effective for waterhemp weed
control. And make sure that you do a good job controlling the late season escapes
there, you know, the escapes will not impact your corn yield however if those
key produce seeds and you're going to
soybeans next year you know those weeds will be there and it'll become more
difficult for you to control them in a soybean year. So you know this is what we
as a weed science community say to our farmers all the time, "If you have no
seeds, you're gonna have no weeds so do the best that you can to not let
those troublesome weeds produce seeds." So, with that, I just want to thank you for your
attention, if you have questions, I have my contact information here. In this light,
I'll be happy to discuss herbicide programs or if you have you know some
specific questions or some things you would like to discuss just feel free to
reach out to me. Thanks again.