Welcome back to the war against weeds Podcast. I'm Joe Ikley, extension weed specialist at North Dakota State University. My co host today is Dr Sarah Lancaster, down at K State Sarah, how are you today?
Doing great. mourning the Chiefs lost. We're recording this the day after the Super Bowl, so the entire state is in morning till you get to the Denver Broncos fans,
I'm an eight hour drive from any any playoff team, so found better things to do, but we're not talking football, although we'll see if any references weave their way in throughout the course of this. But our guest today is Dr Bill Johnson at Purdue University, repeat guest. So Bill, welcome back.
Thank you for having me. Glad to be back. Good to see you guys again.
And in case people haven't listened or don't know who you are, we should go ahead and have you reintroduce yourself and all the great things you do at Purdue.
Oh yeah, yeah. Well, yeah, thanks for having me again. So again, my name is Bill Johnson. I'm an Extension weed scientist. I've been at Purdue for about 23 years, and prior to that, I was at the University of Missouri. So I've always had an extension appointment during my faculty career. So I've been able to see a lot of trends change over the course of time. And one of the interests I've always had in my research program are interactions between weeds and other plant pests.
Those are the things I enjoy talking about as well.
Well, that's a good segue into why we had you on. And so I figured I would start with a question I know you get about at least March, if not this time of year every year. So in eastern the eastern Corn Belt Bill, what are all those purple flowers in the field?
Yeah, well, good question. So one of the things that makes many of our no till fields so colorful in the spring of the year are weeds that have different colored flowers. So the purple flowered weeds are actually from the mint family, and henbit and purple deadnettle are the two most common ones that we see that that have these purple flowers in our no till fields.
And so what makes those two mint species common?
Well, they're winter annual weeds. They survive in a system where they can emerge before the crop is harvested in the fall. So as these fields retain a little bit of moisture in the fall from the leaves falling off the crop plants, these weeds will germinate very shallow in the soil. They're able to survive the harvesting operation because they're low growing weeds. They grow below the cutter height, or the or the head height for a corn machine. And then they have
the ability to establish on many different soil types. They tend to like wet soil types in particular. And then they will survive the the winter months, and then they resume their life cycle in the spring, where the purple flowers typically come out when, when wheat starts to green up. And then they'll, they'll go on and produce seed shortly after that. And then once the weather temperatures are typically in the 80s for on a regular basis, and they, they can, they senesce and die and
drop their seeds. And the process starts all over in the fall.
I know you mentioned no till, but have a conventional tillage. Are they? Are they often found in those I mean, I know there's an easy way to terminate them in that system, but are you seeing a lot of the henbit and deadnettle in these conventional tilled fields as well.
Well? Good question. So, yes, we can see them in conventional till fields as well. I think particularly if you have a situation where we've harvested the crop early and we have an extended fall, and we have good moisture in the fall, these weeds can, can come up in a situation like that. And you know, I think if you think about our the changes that we have going on in our climate, regardless of what the causes are, the Falls tend to be longer than they were many years ago.
So I think, you know, as we get that early, early harvest taken off the field, these weeds have a chance to germinate and establish in the fall. And I will also note that many winter annual weeds also have the ability to germinate and grow in the spring as well. So I think particularly as we get to the center and southern part of the corn and soybean growing areas, spring starts really early. And so when we start having these 50 and 60 degree days in February, we can get some spring emergence
of these, these weeds as well. And that can happen, whether it's in no till or in conventional till.
Sarah, the focus so far has been the eastern Corn Belt. But do you deal with the mint families there in Kansas?
Not in the western part of the state, sort of as you drive west along Interstate 70 in Kansas, you trade fields of purple for kochia in the fence lines. That's sort of how you know when you're in western Kansas. I wondered, though, Bill, do you think it would be maybe interesting for some of the listeners to just talk about some of the differences between henbit and purple deadnettle.
Yeah, yeah. I think the there, it's very easy to to confuse them from a distance, they have kind of a rough leaf texture. When viewed from the top, they also have the purple flowers as well. But if you, if you pull the plants up and hold them side by side, and there's a lot of good images you can Google them, and there's a lot of good images you can pull up on the web. Purple deadnettle will have more of a triangular shaped leaf, and the leaf will actually have a short petiole
between the leaflet and the stem. And henbit tends to produce these sort of half moon shaped leaves that tend to stick almost directly onto the stem. Now both plants will have a square stem, and that's how we differentiate plants that are in the mint family, but again, very easy to confuse them. And if you pull them up and look at them closely, then it's pretty easy to tell them apart. One thing that we see a lot of as well as it's rare. It seems like it's it's somewhat rare to have hand
bit and purple deadnettle in the same field. We tend to have one or the other, and it's kind of rare to have both of them. And I don't know the biological reasoning for that. That's just been an observation through some of our survey work.
So besides nerds like us, who like to identify stuff and get asked these questions, does it matter for management, which one of the two you have
no in the in the work that we've done on no till weeds, that it doesn't matter the herbicide program for controlling both is going to be the same.
And so I'm also partly asking so, I mean, I spent time in these areas of the country, but I've seen henbit, not deadnettle here and only in garden beds around campus, typically not a weed that we find in fields here. Our our winter annual choice that, well, we've got several, but field pennycress is one that kind of dominates our landscape a lot of the time.
Yeah, and if I remember back from my days in Missouri, it seems like we had more henbit in Missouri than we did deadnettle. And then when I got east of the Wabash River, seems like we have a little bit more purple deadnettle than than henbit.
So circling back to control conventional tillage, hopefully your spring tillage operation will take these things out. But what about different herbicide programs, herbicide timings? Any commonalities or differences between corn and soybean?
Well, I think the common ingredients would be roundup in two, 4d obviously, they're going to be low cost and very efficacious on a number of different weeds. I think you know, we started to use a lot more Dicamba recently, as well as the prices have come down, and we've had the availability to to use the trait in soybeans, so we haven't needed a long pre
plant interval. So I think if you start off with those basics, if you're looking for residual control in soybeans, a lot of the classic, the herbicides that contain classic or metribuzin in them give you good residual activity. Other herbicides that contain pursuit, scepter, firstrate and things like that
seem to work fairly well on on these as well. When you're in a soybean system in corn, again, it's it's roundup, 2,4-D, sometimes there's some simazine that's used in the fall that does a good job of suppressing it and kind of persisting until the spring to get some of the spring germinating cohorts as well. And then many of the Atrazine pre mixes that you'll use in the spring will have some some decent activity on on a lot of winter annual broadleaf weeds.
So plenty of options and those two staple crops, what about do you have any questions about them in winter wheat, so controlling it actively within that crop?
Yeah, yes, we do. Typically, where the wheat stands are thin and Sarah is going to be our wheat or actually both you guys are going to be our wheat herbicide experts. You guys have more wheat in your two states, and I've probably seen in my entire life. But you know, in the eastern Corn Belt, typically, the harmony type products work fairly well on a broad spectrum of winter annual weeds, and they work on hebit and deadnettle as well.
I'm spring wheat, whole different portfolio. So Sarah has fill in the gaps here for this particular situation.
Yeah, harmony. And one of the things that I see going out a lot, just, you know, talking with farmers here is like a top dress with MCPA, right? So you put your nitrogen fertilizer and going with some MCPA, you try. To avoid 2,4-D and wheat for crop crop safety concerns, but that'd be another one that's pretty cost effective and pretty easy for folks to do.
So begs the question, I guess for both of you, maybe then pretty popular herbicide choice within the system. There ever get phone calls of it just not quite working. I don't think we've documented any resistance in these weeds. But
I think with the Spring application, sometimes Yeah I was just thinking within wheat, I don't think I've even the speed of activity isn't what people would like to see. And I think that's that's really related to the cold weather conditions. You know, sometimes in the fall, if we do these fall applications, really late in the fall, like second half of November. It seems like the the weeds would just kind of sit there forever and not do anything. And then when you come
back in the spring, they're gone. They they've died over the winter time. So I do think, you know, you think about roundup and 2,4-D as your base herbicides, or systemic herbicides. They just don't work fast when it when the weather conditions are cool. heard of group two resistance, and those two mint plants versus, I know a common chickweed can be more common, and that does have some group two resistance within our our wheat crop
well. And I was thinking, Dallas had I was thinking they had a population of hidden bit. I was trying to look it up.
Are you sure he wasn't just growing it because it's the same color, purple as your, uh, your logo down there.
Theyre not royal purple, more lavender, right?
I think that means stay off my land if you're a hunter. I see all the fence posts painted that color.
Well, it's about this time every spring we get the Facebook posts and Twitter posts about henbit should be a cover crop, and so we can talk a little bit more about why that's not the case later. The other the most interesting thing I've seen in a field of henbit, though, is somebody taking, like, formal pictures. It was a teenage girl in a formal dress in this field of hin bit, oh, sister. Okay, so yes, 2014 henbit, group two from Kansas.
Okay, which? Which group two was it?
They tested it for Glean.
Okay. which, That was probably western Kansas, right? That's where a lot of glean would have been used?
wheat on wheat acres there.
Central Kansas, yeah, okay, I had to guess I would say kind of that I 135 US, 81 corridor.
You know Sarah you're not helping the case at all. Resistance starts with you and Dallas,
Blame Dallas, not me. This is Dallas. This is not me. Passenger here.
All right. So, yes, there is some group two resistance, but not very widespread. So kind of transitioning then. So plenty of you know, plenty of control programs within the major crops where these, these two weeds, tend to thrive and relatively easy and cheap to clean up. So what's the negative impact of these weeds? Are they just out there being purple flowers and making it look pretty? Or why should we really care about them?
There's really sort of two things that these things will do in terms of impacting crop production. So the first is that in these no till fields, I think, particularly where they have a lot of clay content, they will keep the the soils wet in the spring. They they slow the wetting and drying, because they don't transpire. They're not big, aggressive, high biomass plants, like a cereal rye or something like that is so they don't transpire a lot of water.
So I think that's that's one negative to them. The other thing is that they can serve as an alternative host for soybean cyst nematode. So I'll give some props to my my former colleague at Ohio State, Kent Harrison, started playing around a little bit with this in the late 90s, early 2000s and then when I came over to Purdue, Kent and I were talking and and we decided to put together some collaborative research projects when when he was over there. So we had a we were able to fund a couple of
graduate students to work on that topic. And basically what we learned through those projects is that hand bit and purple deadnettle can support as much reproduction of SCN as a susceptible soybean variety. So they're considered a strong host for for SCN number one and then number two. We also showed that, you know, particularly if you think about the geography from Indianapolis and on south so that that kind of geography, we can get another round of reproductive. Production on
hand, bit or purple deadnettle in the fall. So if you think about you know, soil temps have to be 50 degrees or higher, and typically it takes around 30 days or so to get a generation of reproduction. And we can have the weather conditions in that area that allows another round of reproduction in the fall, so the populations can increase on those weeds, even when you don't have a susceptible crop in the field.
Just trying to think we're not, we're not 50 degrees in the fall, but I've seen our winter annuals hang on into July around here. So that's not something we want, because I don't listen too closely to our pathologists, but they talk about nematodes an awful lot.
Yeah, it is re emerged as one of the scourges of the Midwest with, you know, due to some of the resistance that's happening on the genetic material to the genetic material.
Well, look, and it seems to me like as our soybean acres move west, there's a whole nother kind of group of farmers that kind of need this information because they're not as familiar with soybeans as, say, Missouri bill. So we talked a little bit about herbicides, but I wondered, should we kind of hone in on that timing of application, kind of all versus spring? I don't think we really touched on that for like, a head of corn or so? Yeah,
I think it's worth going into that. And I know Bill would set up that there is some spring emergence. But you know, the time you've been in Missouri and Indiana, what's, what's been the best timing for these bill, well,
in terms of just, just killing the weeds, obviously, when you have, well, they're easier to kill in the fall because they're they're actively growing for a long period of time. They're not in that, you know that winter slumber or hibernation, and so they're just easier to kill in
the fall. I think, when you think about timing, though, you know when I when I recommend systemic herbicides like Roundup 2,4-D, whatever it happens to be, what I like to see is daytime air temps in the 50s and nighttime air temps that haven't got down into the 30s. So if we're kind of 40 and above nighttime, 50 and above daytime, and we have a couple of days in a row of that, that seems to be a pretty good situation from a
herbicide activity standpoint. But I think if we think about timing the herbicide application to minimize SCN reproduction, we literally need to follow the combines with the sprayer.
Because, you know, we if we think about in October harvest timing, if we have kind of a wet September, we can get these weeds emerging underneath the crop canopy in September, and it could be by the time we harvest in October, you've had enough time pass and enough heat units accumulated that you can get another round of reproduction of SCN by the time the combines rolled through the field and you're able to spray in October.
So I think the fall applications, from the standpoint of SCN management, need to go out as early as possible, and it does benefit to have some residual activity with that for these early October applications, to try to keep additional ones from coming up later in the fall.
It sounds like based on just moisture management, you want to target the fall for that purpose of the spring as well. Yes, yep. So I was, I was trying to think back, remember, and you know, you'll be a lot more familiar with the exact work. But you know, what are some of the other just things you found along the way with some this alternative host of soybean cyst nematode, there's a bunch of greenhouse work involved as well as the field work,
yeah. And I was just reviewing that publication prior to to this meeting. So essentially, we we identified six hosts that were fairly common in the eastern Corn Belt. So henbit and purple deadnettle were what were fairly common, but common chick weed is considered a weak host, small flower, bitter crest shepherds, purse and field Penny crests are
also considered to be weak hosts as well. Common chick weed is is typically found in the highest percentage of the of the no till fields in the eastern Corn Belt. But it's not quite as strong of a host as henbit and purple deadnettle are. So those are the six winter annual weed hosts that we have found. We've done some work too with, you know, with some of the cover crops that can be suppressive on on SCN, and haven't had a lot of great luck with that. There's, there's some varieties of annual
rye that are supposed to be suppressive to SCN. So we've done some field and some greenhouse work, and it hasn't really shown much of an impact on SCN population densities. So I think that's there's still more work to be done with that as a management tactic. So right now, what I would say, if you're if you're managing. Um weeds to manage SCN herbicide applications as early in the fall as you can possibly apply them, is is going to be the preferred strategy.
So what I'm hearing we have these weeds and a lot of acres, causes a lot of questions in the spring, still some good control programs and some good reasons to control them.
Yeah, I think that kind of that kind of sums it up.
Never would have thought that in just about 20 minutes could answer all these questions and stave off hundreds of phone calls each spring. Did you bill?
I hope that's the case.
Sarah, do you have any other lingering questions? We kind of got through the list I said, I don't think I said this at the odd set won't so I hit record, but figured we might be pretty efficient with this one.
Yeah, there was something that had. Oh, did you look at any weeds that were not hosts? You rattled off the six that were.
yeah so Valerie did that work. Valerie and Earl did that work in my lab, and Kent had a student. I don't remember that student's name. Kent actually screened. So Kent actually has a paper and weed technology. Kent screened a bunch of weeds, winter annuals and summer annuals. And I don't remember exactly what that showed. So we never did that work. Since Kent did that work, Joe, there might be somebody at South Dakota State that's doing some work on this.
I think Sharon Clay had done some, some of that work. So I'd have to, she would have published in Weed Science, but I have to go back and look what she did. But I seem to remember her identifying field Penny crests. So maybe, I don't know there's a, I can't remember she classified as weak host or strong host. Or maybe there's some bio type differences between the SCN and the Dakotas, or the field Penny crestes of the east versus East, Corn Belt versus northern plains. But I
seem to remember that one rising to the top of her list. Or maybe it's just because field pennycress is everywhere up here.
Yeah. Well, yeah. And I was, I was going to say, from what I remember, there weren't any summer annual weeds that were nearly as strong of a host as these winter annuals are. You can get some reproduction on some of the summer annuals, but it's not nearly the amount that you can get on some of these winter annuals. For some reason,
does make me wonder. There's one summer annual we have, and it's it's kind of fun when it shows up in a plot, because we, we tend to kill it with a lot of our corn soybean herbicides. But Lance leaf sage is another mint that we deal with and Sarah, you probably see it on occasion further south, but we can get the occasional field where it's just thick Lance leaf sage. And if you're in a any sort of Roundup Ready
soybean, we've got plenty of options. Are in corn, but a lot of our specialty crops, we don't always have the best control of Lance leaf sage. Of I'd be curious about that one where we get patches it's thick and it's a mint, but it's not the widespread just endless fields of purple flowers, like some of these winter annuals can be, yeah?
I think the thing to do is just, you know, pull up some plants and knock the soil off and see if you see any cysts on the roots. That's they're pretty easy to diagnose that way,
yeah, because all of those winter annuals you listed, you know, a lot of them are mustards. And so I'm thinking about our mustard populations that we sometimes get in our wheat fields and then and areas, particularly in the southern part of the state, will go ahead and double crop soybeans into that so I'm just wondering what kind of extra problems our guys are setting up for themselves in that scenario.
Yeah, well, and then pennycress and pennycress would fall into that mustard family.
Wondering if I've seen anything, they've tested canola. I'm sure they would have had to have but that's the interesting one I hear most about from our pathologist. Besides soybean is some dry bean varieties tend to be very susceptible to SCN too but I haven't heard them mention any of the other crops that we're typically dealing with well. So we should probably go ahead and wrap this one up then. So Bill any, any parting thoughts of on henbit or purple deadnettle?
Well, I think again, if these weeds are, you know, causing problems in your field, and you also have some kind of unexplained yield loss, I would have your field tested for or sampled for SCN as well. And always keep in mind that in terms of SCN management, planting genetic material that has resistance to SCN is always a great strategy, and herbicide applications can kind of help nibble at the edges, but it really shouldn't. Be the big hammer that you use for SCN management.
All right, now we're getting dangerously close to a pathology podcast. We really need to wrap this up now. So, but before we go, Bill, do you want to the folks know where they can find you if you're still active on any social media, or
if I could remember those uh, Twitter sites, I probably would.
We'll find you, see if you're active, and tag you in the show notes. But with that, we'd like to thank you, Bill for coming back on and then talking about these couple of weeds with us. Thanks, as always, to the listeners, and we'll catch you next time on the war against weeds. As always, we thank you for listening to the war against weeds podcast. Just another reminder, you can find our podcast hosted on the Crop Protection Network, or CPN, for
short. So this is another great resource that's driven, by extension, scientists at different universities for pest management. And with that, we will see you next week on the war against weeds podcast. You.