Music.
Welcome back to the War Against Weeds podcast. This is Alyssa Essman, Weed Science extension specialist at Ohio State. And today I'm joined by my co host Joe Ikely, Weed Science extension specialist at North Dakota State. Joe, are you ready to get spooky today?
As long as someone sends rain, I'll do anything.
All right, so we've got two great guests with
Sure. I'm a professor in the Botany and us today to talk all about kind of an interesting species as we Plant Sciences Department at UC Riverside. I've been at this head into the Halloween season, and that is witchweed. So we have Dr David Nelson and we have Dr Bridget Lassiter. Dave, do you want to start out and tell us a little bit about what you particular position for about eight years now, and my lab is do at what you do at UC Riverside?
interested in how plants sense signals in their environment or internally, and then how they convert that into developmental or growth changes. So one of the signals that we study are class of compounds known as strigolactones, which are involved as plant hormones, and they're also going to be related
to witchweeds, as we'll talk about later. And we also study a class of chemicals that are found in smoke, known as karrikins, and they help plants grow after fire, but they also seem to be involved in a lot of other aspects of plant growth.
Interesting. Thank you for joining us today. Sure. Bridget Do you want to tell us a little bit about what you do?
Yeah, absolutely.So. I'm the superintendent at a research station in North Carolina. We're about five miles from main campus from at North Carolina State University. This is an 1800 acre research farm. We have about 30 different units out here, so we raise lots of different kinds of crops and lots of different kinds of animals, dairy cows. We have a creamery here, so we serve ice cream to the public. And so our mission here is to make sure that any students, any professors, can come here and
have a lab, because we are only five miles from campus. We also do a fair amount of research out here, and we have several big extension field days out here. But prior to this job, I've been here for about four and a half years. Prior to that, though, I worked for our State Department of Agriculture and worked in the witchweed eradication program, which is really the only invasive species, invasive weed eradication program that the
federal government has ever funded. And so while I was there working on that program, I learned a lot about the history of witchweed and it's a very unique species, you know, not native to North Carolina or or North America really, and, you know, learned about the people that did a lot of research on this species to try to figure out how to control it in the United States so that it would not affect the Midwestern Corn Belt.
Thank you both so much for joining us. It sounds like you guys have kind of a range of experiences working with this witchweed. So let's go ahead and dive in here. What are, you know, some of the characteristics that make witchweed unique,
you know, yeah, let me take the easy ones. Okay. So the thing that makes witchweed really interesting is that it's a parasitic plant. And, you know, Dr Nelson is gonna be able to talk about this a lot more in depth than I do, but you know, parasitic plants need a there's obligate hosts. They need a specific host plant in order to grow. And the other thing that is interesting about witchweed is the seeds are really, really small. They stay in the soil. Have been observed
to germinate up to 14 years after deposition. So when you're thinking about how to control a plant, you have to think about the host plant that it lives on. You have to think about moving soil around and making sure that you're not having it on your tires and your feet people that enter those fields. And then you're also thinking about, you know how small those seeds are?
Yeah we have to think about that. It sounds like over a fairly long period of time to ensure that eradication, if that's the goal. Dave, do you have any additional thoughts on some of the characteristics of witchweed?
As Bridget indicated, it's a it's a parasite. But there are different types of parasites. Some of them are parasites of shoots. So many of you are probably familiar with mistletoes, for example. And these are, in fact, root parasites, which are found within this larger plant family called Orobanchaceae. And in that family are many different types of root parasites, the Witchweeds are just one of them. Broomrapes are another common example of the parasites that we think about in agricultural
settings. And so one thing that makes these parasites really special, as Bridget mentioned, they make lots of seeds. So a single Striga plant can produce 10s of 1000s to hundreds of 1000s of itty bitty seeds, and that makes them really hard to i. Uh, you know, decontaminate equipment and and it's pretty difficult to get them out of the soil once they're established there, because, as Bridget mentioned, they can last for
10-20 years or more. But what makes them, I think, really special, is that these seeds that are laying in the soil are able to basically wait, lurking in the darkness, if you will. They're waiting for a host plant to be nearby, and they delay their germination until they can sense a host plant is nearby. The way they do that is they pick up on chemical signals that are coming from host plants roots, and then that triggers their germination. For Striga in particular, these witchweeds.
They're super tiny seeds. And so when they germinate, they can only grow for a little bit, a few millimeters, typically. And if they don't succeed in attaching to a host root within that short time period, usually a few days after germination, then they're going to run out of resources and die. And so they've evolved this really amazing ability to wait until that host is nearby so that they that improves their their
likelihood of successful attachment. And that brings us to one other feature that's really important to think about with parasites, which is that they have this root like structure that allows them to basically tap into a host root. It's called the haustorium. That's something that we find in
many types of different parasites. Basically, it's just a way to invade the host root and connect to the vasculature, and then, like little vampires, these these witchweeds, can then extract nutrients from the host.
So and Dr Nelson alluded to this. You know, in order for that witchweed seed to germinate, it has to have a host but we, Dr. Eplee was a a research scientist who worked for the United States Department of Agriculture. He worked for 30 years in southeastern North Carolina looking at the biology and control measures of this weed. So one of the things that Dr Dr Nelson alluded to was that these
seeds have to have a host in order to germinate. So in North Carolina, when this plant was discovered, you know, the story that everyone tells, who knows if it's actually true or not, the story that everyone tells is that the farmers in southeastern North Carolina were seeing some symptoms in their corn crop that looked like drought. And so they called the extension specialist down to that area, you know, it's like a three hour drive from Raleigh back in the 50s. And they said, Hey, we're having
problems with drought. What's going on here? And so the professor brought a graduate student with him, who happened to be from India, and witchweed is native to India and Africa and parts of Asia? And he said, Well, look at this. And he found this little, tiny plant. You know, witchweed has a beautiful, bright red flower on it, but it really only grows to eight to 10,10, inches tall. So you're in a giant cornfield, and you have an eight to 10 inch tall weed growing just adjacent to the
corn plant. And the graduate student said, this is a bad plant. This is in my home country, and this is a very bad plant. And no one in North Carolina, or probably the US, had really ever studied this plant before. So in an official quarantine was established in North Carolina in september of 1957 and that really hurt North Carolina farmers, because they couldn't move their crops around. And so each you know, their farms were quarantined. But also there were entire
county quarantines. And so Dr Bob Epley was a USDA scientist. He started researching witchweed in 1965 and he worked for 30 years. He didn't retire until 1995 and one of the things that he discovered one of the control mechanisms that we can use for
witchweed is called Suicide germination. And so he developed, he developed equipment that we could put into the field, and we inject ethylene, which is like a ripening gas, you can inject it into the soil, and that ethylene will cause the witchweed seed to germinate, but in the absence of a host then it will die, because it actually can't connect its hostoria into the roots of the host plant. So long, long story to to explain suicide germination.
We need suicide germination for every weed we deal with.
You know, from a control mechanism standpoint, that's why I love to tell the story about witchweed control and eradication. We're 99% eradicated in North Carolina. But, you know, I think young people these days, and I'm including myself and young people, you know, Roundup came out, and you know, we had Roundup Ready crops in like 1996, 1997 so Roundup Ready crops have been around my whole life, basically in my career, and we've always been able to
spray Roundup. But. But you know, this quarantine started in 1957 they didn't even most farmers didn't have any mechanism to spray pesticides all across their fields. So you're not only using pesticides to control witchweed you're also using, and we still use humans to hand pull those those plants. We still use a bounty method. So if a just a farmer finds witchweed growing on his farm, he can report it to the USDA, and he gets a check for finding that weed. 15 whole dollars.
It's done the same amount the entire time.
So are there other wanted posters up across North Carolina? I
wanted to make wanted posters and put them in post offices.
$15 reward.
Yes, big reward. So when you talk about integrated pest management, the Witchweed eradication program really utilizes integrated pest management, because we don't just use pesticides.
Have they lifted the quarantines on some of those locations in North Carolina,
so the quarantines are now just on a particular farm. It's not the entire county. So I like to tell the history story you know, so witchweed was first discovered in North and South Carolina in 1957 at its so they started employing grad, you know, high school students, college students. At this time, the USDA was in charge. Every old farmer around in those counties worked on the witchweed eradication program, like when they were in college. So at its very worst,
in 1978 was the data that I was able to find. In 1978 there were 309 853,000, acres in North Carolina that were infested and in South Carolina. In 1978 there were 72,588 acres. So all told, in 1978 between North Carolina and South Carolina, there were 382 441,000 acres infested. So you know that was 39 counties in North Carolina, five counties in South Carolina. Those entire counties were in those quarantines. You could not move
corn in and out of those areas. You know, the USDA was really concerned about not getting this weed to the Midwest Corn Belt, and that's really kind of the basis for the entire eradication program.
So I have to ask the dumb question you mentioned, hand weeding. I'm familiar with the pulling any other weed out of the soil and and how that works. Will you do more damage than good hand weeding? Because they're, they're directly tapped into the corn roots. And so I'm just curious what that process looks like compared to hand weeding any other weed that we that we deal with.
Yeah. I mean, in in our estimation, it does zero damage to the corn root, right? Because a parasitic plant is actually sucking nutrients out of the corn root. So if you remove that parasite, just like treating fleas and ticks on your cats and dogs, once you remove the parasite, they're fine. They're actually better for it. So your scouts go out, they hand pull, they visit each each infested field about every two weeks. They hand pull the plants, put them in plastic
bags, and then we incinerate the plastic bags. So we're trying to reduce the spread of seed.
So it sounds like, you know, as we've alluded to, this is a really different weed than we're used to dealing with in our corn and soybean systems. It's, it's got this parasitic nature. You know, it kind of pops up, sounds like once the damage is kind of started. So I'm curious, you
know, how do these characters influence management? I know we talked about suicide germination, but do you have any other thoughts about how management of the species is different than some of these other weeds that we deal with?
Sure, so there are a number of approaches that are being used to try to mitigate witchweed damage. And so I'd say, you know, in the US, while it has been a threat, it hasn't been a serious agricultural issue. And so a lot of the work that we'll talk about is are approaches that are being used in Sub Saharan Africa, where this is affecting 10s of millions of small holder farmers. There are also problems with related parasites, broomrapes, specifically,
particularly around in the Mediterranean area. So if you look in southern France, for example, or in Israel, there's a lot of parasitism of sunflowers and tomatoes that goes on from these broomrapes and so, but it's similar ideas. And so in terms of management strategies, one of them is this idea of
suicidal germination that Bridget mentioned. And so one way you can do that is by applying chemicals that might stimulate the Parasites to germinate in the absence of a host ethylene is one of the things that may work, at least for some species. But another idea was to basically create mimics of these chemicals that the seeds are normally sensing from host plant. These chemicals are referred to as
Strigolactones. They got their name from being germination stimulants of Striga species, which is another name for witchweeds. And so the trouble is that strigolactones are kind of expensive to make, and so it's not necessarily something that is very cost effective, especially for a smallholder farmer who has limited access to pesticides and fertilizers and other cost intensive inputs. And so there's been an effort to try to make simple analogs of struggle lactones that can trick
these seeds into germinating. And the idea there would be that you would, you'd spray a field with that and help reduce the the seed bank by triggering that suicidal germination. But there's also interest in biological methods of stimulating suicidal germination. One way you can do that is through rotation cropping. So some of the parasites are generalists, and they have a fairly broad host
range, and some of them are more specialized. But even within the generalist there will be some crops that they're not able to attack. That can be due to structural differences in, say, the root that resist penetration from that invading parasite. It can be through immune like responses, where they recognize that there's an invasion, and then they cause hypersensitive
death of cells locally to help kill that parasite root. And then there are other forms of resistance that involve modulating the amounts and types of strigolactones that are, that are are made. But with these rotation cropping systems, you can have a plant that's producing these struggle lactones, but isn't a compatible host, and so that can trick the weeds into germinating, and then they fail to actually attack, and so then they die. And so that type of system has been
popular. There's also a lot of research that's going on now looking at ways that we can use microbes, bacteria or fungi to either stimulate germination of the parasites or to kill them, to physically destroy them. And so there's some interesting systems that are going on there.
Yeah, so you mentioned something there that caught my ear. I don't know if we've mentioned this yet. I guess when I think of witchweed, I often think of corn are, is witchweed specific to grass crops or a certain set of crops?
Depends on the species that we're talking about. So among striga species, there's striga harmonica and striga asiatica are some of the most prominent weeds, and among them, they're able to parasitize rice or maize, corn.
Isn't there some that doesn't there's also striga gesnerioides.
That's right,
well on myresearch and the list. So I have a lecture that I give to my let me tell you what my slide says. Hosts of those three species could include corn, rice, Pearl millet, sugar cane, foxtail millet, sorghum, finger millet and rice grass pass palum. Those are kind of, kind of the like the big crops that we would harvest for food
And striga gesnerioides, it also it attacks legumes, like cowpea, which is a major staple crop in Sub Saharan Africa.
That seems a little crazy that all of a sudden it just decided it was also going to attack legumes.
I mean, these are highly adaptable species, and part of that's probably a consequence of the fact that they make so many seeds, and so when you have an enormous effective population size, you know that means that there's a good chance that some fortuitous mutation will come up that allows one of these parasites to be successful. And then, you know, we have a tendency to grow the same crops again and again
in the same fields. And so there's a, you know, it's possible for for new things to arise, yeah, okay,
my follow up question. So a little bit of background. So my PhD, I got to work on bacterial disease of corn, and I worked on alternative weed hosts. And I heard foxtail millet, which I know is a setaria species. So are some of the weedy setaria species also host. Is that even known?
Well, we do know. I don't know specifically about sattaria, but I do know that, um. Um, weedy crabgrasses in North Carolina can also be hosts. So if we're in so, you know, from a control standpoint, if we're in a roundup ready corn, we want to make sure that we're getting out there and putting our glyphosate out, you know, at the right timings to control any of the grassy weeds, because they can be alternate hosts.
Darn. Digitaria strikes again.
So this might be a good opportunity, as you guys kind of bring up some of these areas of interest, to let you talk a little bit about your research and your experience with this lead Bridget Do you want to talk a little bit about some of your experience? I know you've mentioned the eradication program.
Yeah, really, my experience is the eradication program. By the time I came on, the North Carolina Department of Agriculture had taken over the program from the United States Department of Agriculture. Really, USDA wanted to divest
themselves. They still fully fund the program, but we have kind of local control of the program, so I just managed, you know, those summer, summer helpers that we would hire, and our full time employees and our whole fleet of, you know, we had several research stations just dedicated to operations to go out. It takes a lot of driving to get around to all these fields. And we try to get to every infested field every two
weeks. So as far as North Carolina goes, we were just using the research that was that had already been completed, and trying to, you know, get to that 100% and everybody always asks me two questions. Number one, I say, hey, yeah, I work on the witchweed eradication program. And they say, witchweed? Are you still working on that program? And then the follow up question is, Will you ever eradicate witchweed in North Carolina and South Carolina? And you know, really, I don't know the answer
to that question. It brings up such a huge conversational point when you talk about eradication, because weeds and insects are different, we have eradicated insects. Can you eradicate an invasive species that is a weed that you know, produces millions of seeds that are the size of dust? It's going to be really hard. But all of that, I say, all of that, I don't think we should give up, because according to my research, and
there may be more updated research. According to my research, if you had a fully infested field of corn, you would have 35% yield losses, and it could be higher, you know, I don't know what Dr Nelson knows about yield losses.
Actually I was going to ask you Bridget if, if, witchweed really poses a strong threat to US agriculture, given the amount of fertilizers that we use and the amount of pesticides, herbicides, I should say, that we use to control weeds, it's a very different situation, I think, than what a smallholder farmer in Sub Saharan Africa is going to be
facing. One thing with the use of fertilizers is that that reduces the amount of these chemicals that the plants are sending out into the soil that the witchweeds are sensing and taking advantage of, and so there's less of that germination stimulant there. And another thing is that I think with the increased nutrient availability, what the parasites draw off isn't quite as problematic in terms of how it affects yield.
And then I but, you know, I don't know, like, do you? Do you know more about how that?
Interesting that you bring that up, because I was looking at these slides, I hadn't really thought about witchweed in a couple of years, and so I looked at the environmental requirements for witchweed to germinate in a cornfield. And as far as soils go, witchweed wants a sandy soil, infertile, dry and low nitrogen, infertile and low nitrogen, kind of the same thing. So you think, Well, how many of our really productive fields are Sandy, dry and
fertile and low nitrogen? Not too many. And so I never actually saw an entire field fully coated from corner to corner, edge to edge. I never saw a field fully infested with witchweed I always just assumed that's because we had been such done such a good job with our eradication program that we just had these little tiny pockets. But possibly these little tiny pockets were only in the worst parts of the fields. So it's a
valid question. Maybe we're scared of something that wouldn't actually come to fruition as as being a huge threat for, you know, modern agriculture, but for smallholder farmers, it is a huge threat for people that are eating everything that they're producing, they need everything that they can produce.
Absolutely.
It's a question that the USDA is asking right now, actually, because they would like to, they would like to figure out how to not send so much funding to the witchweed eradication program. Again, it's very important. We cannot give up on this program.
I think it's important. Hard to keep it under control. But I do, I do wonder how much of an economic impact it would be, and if, you know, got the Midwest, would it be a big deal? Or maybe it would be fine. I don't know.
I mean, the pictures that I have of a fully infested field are from 1965 where we didn't have, you know, really high yielding varieties of corn. We've had so many advancements in agriculture since then that we probably in the United States, we don't have a good control where we can look at a fully infested field and a fully non infested field, you know, and see what the difference would be between yield losses.
Now the broomrapes can be, continue to be problematic, even when we have fertilizer inputs.
So, you know, you can come to North Carolina and see broomrape too.
Oh, I'm sure, yeah. I mean, we're just talking about some of these, these plants that have really emerged as as weeds. But there are many species in the Orobanchaceae that have these natural relationships with native plants. And, you know, they have an effect, but they're not wiping out their host. If you've wiped out your host, it's a bad thing, because then you're going to die, and it's a dead end for a parasite. And there are also many parasites in this family that are more
opportunistic. They don't have to engage in parasitism to survive, but they may do so if an appropriate host is nearby. And they kind of like cheating, you know, just steal some stuff while you can, but they don't have to do it. And so there are many species that that are like that,
but isn't witchweed, It has to have a host, correct?
Witchweed is, witchweed is an obligate parasite. It, it still is, is somewhat photosynthetic, but not very good at that, and most of the damage it's doing is while it's underground. But there are some, some parasites, like these broom rapes, which are completely not photosynthetic.
Yeah, they're white when you find them out there.
Theyre dependent the entire life cycle, witchweeds are also dependent, especially for that early phase of growth. But yeah, you'll see even in the southeast, is it called. There is a canophilus americana. I'm trying to remember the common name for it, but that's something that you can see in the forest out there. It's a parasite of trees like
beech, and I think maybe oak. And you'll see this, you know, coming up out of the ground this, this kind of, kind of looks like a pine cone of sorts, but sticking straight up and pale. Yeah, the parasites are amongst us.
you know, one thing that was coming to my mind we mentioned, really no field wide infestations can be found. Is one of the things Alyssa and I deal with and talk about on a daily basis with large production agriculture, is that combines are the greatest spreader of weeds. But if we have a weed that's mainly the crops we deal with corn and we're not going to feed and it's eight to 10 inches tall, that's not going to go through a combine and get spread that way.
So it's really more tillage, if for those who are conventionally tillage and some other applications. So it's based on how a lot of our modern agriculture and the big ag producing areas are, it's doesn't seem primed to spread quickly, like some of the ones that Alyssa and I have to deal with on a on a daily basis.
I don't know. I might argue about that, Joe, um, because I know witchweed seeds are wind blown so they can they can spread on wind. There's the part I missed. They can float in water, and they will attach to a tractor tire in a heartbeat. And I have spent it. When I was in this program, we spent 1000s of dollars fumigating equipment that had come into an infested area to do some they were building some new chicken houses, and we could not release that that excavator
until we had fumigated that equipment. So in very rare cases, we still get to use methyl bromide in North Carolina, by and large, that practice was abandoned in 2010 you know, for widespread fumigation in fields, but for equipment we still utilize it.
I'm glad I asked the follow up, because learn some more about the seed biology.
I don't know. Maybe I'm just scared of this tiny, little eight to 10 inch plant. I don't know!
No, it's the same thing, like we've the other the windblown seedless, and I would deal with this horseweed or Marestail. And, yeah, we're not spreading that via combine. So wind blood or wind blown sticking the tractor tires makes a lot more sense how it can spread easily.
So Dr Nelson, have you been to other countries where witchweed is growing and affecting small holder farmers. Have you seen this? You know? You know, like on their farms,
I have not seen the plant in person. I have, I have visited some farms I had the opportunity thanks to the. Bill and Melinda Gates Foundation to visit Kenya, probably a decade or more ago, and got to interact with some small holder farmers, as well as some researchers who are working on Sub Saharan African agriculture and the witchweed problem.
So I do know that this is becoming a bigger problem in Australia, and so I think they're doing active research on it in Australia, and they may have done some more, you know, some advances moving forward, looking at some of our new chemistries to see what their efficacy is on controlling
witchweed. But I don't think that. I don't think we should let it go in the US, because I think it is becoming a bigger problem in Australia, and that, you know, their their agriculture systems are very similar to ours, so seeing that they're having problems, I don't have any firsthand knowledge in Australia, but I do know that they reached out to us trying to fabricate some equipment to put ethylene in the soil, and they were trying to figure out How we had done it so somehow, which
we've got to Australia, maybe in the last 20 or 30 years?
Yeah, I think it's best to keep that genie in the bottle as much as we can.
I think it's maybe safe to say that Joe and Bridget and I think of it very much from a sort of applied management perspective. But I think Dave, you have sort of a different experience, and in some of your research, could you talk a little bit about what you've done?
Yeah sure. So I got started working on on parasites. Indirectly, this began for me. I was interested in how plants were able to sense chemical signals in smoke, and how they can there are many species that are adapted to grow after fire, and so there's a particular class of chemicals in smoke that we call karrikins that were isolated that can stimulate
germination of many of these fire responsive species. And we were trying to understand how plants were able to sense these keratins and then germinate, and a class of receptor proteins were identified that were responsible for responding these karrikins signals. More likely they're they're also responding to an endogenous hormone, which we haven't found yet, but that's
a that's a mystery for another day. But what we found was that in this parasite family, these receptors that were involved in sensing these karrikins signals from smoke in many other plants in this parasite family, they had specifically undergone this large gene duplication, so extra copies of the gene that encode that receptor were found in these parasite genomes, and then many of these were functioning now as receptors for this strigolactone signal, which is being emitted from host host
plants. That's what the parasite is sensing and using as a germination cue. You know, there's, there's one thing that we haven't mentioned so far, which is, why are plants so dumb as to put out? I kept going to like potential attack from a parasite. And you know, that was, that was something that wasn't fully appreciated for a long time. Struggle. Lactones were found in the 1960s but it wasn't until probably about 50 years later that it became apparent why plants were making
these things and why they're exuding them into soil. And so it turns out that plants use these strigolactone signals as a way to communicate with microbes in the soil. So in particular, it's used to help enhance interactions with arbuscular mycorrhizal fungi, which are used by 80% of land plants as a
way to harvest nutrients from the soil. So under low nitrogen or low phosphorus conditions, plants will increase the amount of strigolactone that they put out, which then helps them better recruit these associations with these beneficial fungi, and then they engage in a symbiosis with those fungi, where they trade carbon for nitrogen and phosphorus, and that helps alleviate the problem. And so this can help explain why in fields where there's there's, you know,
nutrient depleted soils. Why the striga problem can become even bigger? It's because these plants are desperately trying to set up these interactions with the fungi, and then they're sending out more of these stimulants that the witchweeds
can then take advantage of anyway. So we found out that these, these keratin receptors, had basically acquired mutations that allow them to function now as strigolactone receptors, so the same overall mechanism of controlling germination, but they changed what they were responding to when germination was being activated, and in these para. Some of them have
become dependent upon that signal in order to germinate. So my lab has been interested in how, how these new receptors evolved, what's going on with them in different types of parasite species. So there are some plants which I mentioned earlier, which are not dependent upon a host, and they still have all of these extra copies of these, these receptors that can that can perceive strigolactones. And so it's been unknown. What are they doing with those if they if their
germination isn't dependent upon strigolactone to begin with? And a couple of years ago, a colleague of mine, Satoshi Ogawa, working in Ken Shirasu's lab, found out that these, these receptors, can be important for guiding a parasite route toward a host. So not just like triggering them to germinate, but also saying, I'm over here and so they can follow this, this, this chemical gradient, to get closer to a host root. And
so we've been trying to understand how that occurs. And yeah, it's been, it's just been fascinating to take a look at how these receptors have changed in different ways to serve
functions such as germination or growth toward a host. One of the goals that we're hoping to achieve as a consequence of this type of research is if we have a better understanding of how the parasite senses these chemicals, maybe that gives us a more sophisticated way to generate chemicals that may be able to activate those receptors and trigger suicidal germination, or perhaps permanently deactivate those receptors. So that's one of the driving purposes for that research.
So side note, one of my favorite byproducts of this podcast is I saw Bridget taking some notes. I'm getting guessing they're going into slide decks. But
yes, yes. Well, one of the things I was going to look up that I forgot to look up before I came here was that when I left that job at NCDA, I went through 30 years of abstracts, because that lab published abstracts every year of all their research. And I'm, I'm guessing that not very many other people looked at those abstracts. So I wanted to give I I scanned them in and just, you know, created digital copies of them. But in the 80s, they looked at using dogs as because
dogs can pick up on, I think it's strigolactone. And so they, they the USDA looked at training dogs to go out into the fields, find the infestation of witchweed and then have humans, you know, pull the witchweed out. They never went any farther than figuring out that dogs could do that work, because along with using dogs, comes a handler and having air conditioners and, you know, giving them breaks every four hours. And it never became an accepted practice to use dogs to
find these weeds. But I always thought that it was interesting research, even though it didn't get applied to this particular pest.
That's fascinating, and I'd never heard of that.
Probably what,
Maybe I can get one of those dogs in my lab. I could use that to measure stuff.
No, I it's just very interesting.
That's cool. Animal funding for a sense, you have to get a short haired variety if you want field applications. Or else, I do some imagining seeds in their coats and spreading the seed.
I think it'd be cheaper than a mass spectrometer.
Yes, Yeah. that's very true. You probably buy a lot of dogs for the price of one of those.
And then grad students would have their emotional support dogs in the lab.
Sure sure. I'lll say, though, that the mass spectrometer doesn't poop.
No, you don't have to feed it.
For whatever reason. Dave, when you were talking, I was thinking, I think there was PBS. Have you seen the video of a parasitic plant like scenting a tomato plant?
Ah, that would be dodder.
Yes it's dodder. Yeah,
that's just a fascinating story. Yeah. I mean, these parasites, they honestly make you question, what is a plant anyway? Yeah, you know, if you don't photosynthesize, if you don't like, in the case of dodder, once these plants germinate, they they have, I think they temporarily have a root. But then they'll they spin around this tendril until they can attach to a host, and then they also set up this haustorical connection, but this time, it's to the Vascularture
into the shoot, and then they're off and running. They don't need a root. They don't make leaves. They're not photosynthetic. It's just this like horrible spaghetti that spreads out like a blob. All over plants and just it's a that is a truly disturbing parasite, if you ask me, yeah, it's able to it's able to sense chemical signals that are volatile, and that helps guide it toward a host. It's pretty wild.
It's one of those I don't think about too much, but I got a couple questions this summer. One was from a field that had it like, 25 years ago, and then now they think they have it again, and like, man, that's some bad luck. yeah. Dodder.
Yeah I mean, you'll, you'll see it like, in California, I see it on the hillsides. In some places. It's just natural populations. But, yeah, yeah, I don't think you want your field, no.
So I guess one of the last questions here, what are, what are some future areas of research, Bridget, I know you mentioned Australia having maybe some active programs. I'm just curious, you know, what are some of the next steps needed to better understand and to manage witchweed.
I think it's probably just new modes of action, since at least in the US, we haven't been doing any active research on modes of action to control witchweed since about the mid 90s. So you know that I think we could take, we could take some clues from what they're doing in Australia.
So there's a few areas which I think are particularly promising. Some of this comes in terms of breeding or engineering plants to reduce their strigolactone output, or to perhaps to change the types of strigolactones that they're making. So there are some, for example, there's some cultivars of sorghum and rice which have been found that are resistant to Striga because of differences in the amounts or types of strigolactones that they're making. I think that's that's a
really exciting area. I'm also very interested in what some groups are doing in terms of using microbes as a way to control, to control striga. So the the ideal solution is going to be something that is is very cost effective and doesn't require a high degree of technology so that it's accessible to small holder farmers. And so one of the projects that I think is really neat is something, it's called
the toothpick project. And the idea here is that they use a they use a fungal species, Fusarium oxysporum, which is capable of of attacking Striga specifically and killing it. And they've basically been selecting for different strains of this fungus that can also produce extra methionine as an amino acid that bacteria can then convert into ethylene, which
also helps stimulate suicidal germination. But the idea is that they they can basically brew a batch of this fungus with toothpicks, and then send that to small holder farmers who can then cook rice, or they're looking into maybe some leftover corn husks, things like that. And basically brew a batch of this fungus, and then they can use this when they're sowing their seeds, to basically inoculate the soil locally. And
so you create this, this defense against the striga locally. I think that's a really neat solution, because it's, it's so cheap and it's easy for the farmers to do themselves. And so they're, they're reporting 50% increases in yields in striga infested fields. And I think that's really think that's really promising. Another coalition is working on a project called promise. There's a very long acronym, which we'll have to look up to get you the right words for that, but the
idea is that by manipulating the soil microbiome. So, for example, the bacteria that are going to be present in the soil, they may be able to do things such as destroy strigolactone, or maybe have some bacteria that make things that can stimulate parasite germination or that can attack parasites. This is a really interesting approach to doing things that, again, may
not require a lot of costly inputs to make it happen. And so that's a that's a Bill and Melinda Gates Foundation funded project, which I think is really interesting to go take a look at. I'll send you a link.
Yeah, that'd be great. It sounds like some very creative solutions, but also accessible, which seems like absolutely a key part here.
There are still many people who are working on this idea of chemical stimulant of parasite germination and. But, and if that can be made cost effective, that would be wonderful, too. So it's all going to, I think, be part of a, you know, an integrated pest management program,
which is a great segue to our final question of the day, Bridget and Dave, is there a silver bullet for weed management,
I'm gonna say no.
Great answer.
We started getting into straggler research. I sure hope there was, and that I could, I could participate in doing that. But it's, it's becoming very clear to me that it there is no silver bullet, and we're going to need multiple perspectives to come up with the more holistic solution.
And I you know this, this is a great time for me to make a point that I wanted to make about Dr Eplee working on one species for 30 years to figure out the biology and the control mechanisms because of his work with witchweed, pretty sure he knew there was no silver bullet, but because of his work in figuring out all these different control mechanisms that would work on one species, he was actually the Weed Science Society of America liaison and helped pass the federal noxious
weed act of 1974 and he was also A really big proponent of forming these state invasive species councils and invasive Task Force. They have, kind of go by several different names, but when I worked at NCDA, I, you know, was the president of the North Carolina invasive species Council, and it's, you
know, it's a group of like minded individuals. More often they don't work in row crops, but they work in non crop areas, and they're trying to make sure that we're not bringing new species to the United States that are non native and so, you know, that's another that's just another bullet. We don't have one silver bullet, but that's another bullet in in our toolbox of making sure that we're not bringing new species here and
not creating new problems for our for ourselves. And so trying to, you know, early detection and rapid response is one of the tenants of IPM. We want to make sure that we're finding those new species as soon as they get here and getting rid of them. Because maybe they're not a bad species in their in their homeland, but if they're here, they don't have their natural predator predators, and so they can become, you know, get out of hand very quickly. So no, no silver bullet. We have lots more
weed species than we've ever had before. We have more tools than we've ever had before, but that. But as you guys know, working in row crops, some of these species are are really hard to control.
Yeah, we need all the tools on toolbox. And now I'm just thinking, can we teach the dogs to dig up the weeds?
I don't know. sniffing dogs. I love the idea of a yellow lab travel around in my truck with me sniffing out weeds.
There's one thing that we haven't mentioned this entire this entire session, which is, where does Striga get its name from, or witchweeds get their name from? So in case you didn't know, Striga, which is the Latin word for evil spirit or witch. Also the Striga, or Striga is a vampiric witch in Albanian mythology and folklore that sucks the blood of infants at night while they sleep and then transforms them into a flying insect. So anyway, it's a vampiric witch. That's where
we're getting this this name from. And I feel like if you're going to do this Halloween related episode, we need to mention it.
Yes, perfect. So do you guys have any lab websites, social media sites, other places where we can find you maybe find information about, you know, witchweed or some of the other work that you're doing? Sure I'm at nelsonlab.ucr.edu.
I don't have any professional social medias. I'm just trying to keep everything above board here at the farm.
Well, then I have one final question for you within Bridget and Alyssa, you were at a different Dinner Table A couple weeks ago when this discussion came up, there was recently a article about the top 50 creameries at universities across the US, and I heard it mentioned earlier. So Bridget you're number one, aren't you?
I don't know if we're number one, but in my book, we're number one.
I think it was.
I think that was the number one my window in my office. I keep it in my freezer at all times. The best flavor is banana pudding. You know, of course, we're in the south, but yes, I I tell everybody that comes on a tour of the farm, it's because of me that you get to eat ice cream, because all of my guys grow the corn and the sorghum and we make silage. That's what we live for all and we have happy cows living right out here on the farm, making ice cream every
day. So yeah, we love our Creamery, our howling. Cow ice cream. And, yeah, it's really fun to be here on the farm and have people you know, learning where their food is coming from, and being able to come here just the public can stop by at any time. Seven days a week, they can stop by and eat ice cream.
So it is very good ice cream. So you'll have to come alright. And one of your other co hosts, Sarah Lancaster, she's, you know, my BFF and I took her there a couple weeks ago when she came to visit her
Oh she didn't tell us that she's sorry. Yeah, she's gonna text right now.
Well, now I want some ice cream. So with that, we'll say thank you to the listeners. Thank you Dave and Bridget for joining us, and we hope you'll tune in next week to the war against weeds podcast. Thanks for tuning in. Just a reminder, you can find this and other podcasts and resources on the crop protection network. This network has a host of information from extension programs across the US about all things pest management. We hope to catch you next week on the war against weeds podcast.