Rice herbicide resistance with Whitney Brim-Deforest

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Whitney Brim-Deforest and Sarah Marsh sit down to talk about herbicide resistance in California rice. Herbicide resistance is continually quoted as a primary concern among rice producers and researchers. Due to a myriad of reasons, there are very few chemistries available for weed control in CA rice; among these, herbicide resistance has been reported in all but the most recent.

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The views, thoughts, and opinions expressed are the speaker's own and do not represent the views, thoughts, and opinions of the University of California. The material and information presented here is for general purposes only. The "University of California" name and all forms and abbreviations are the property of its owner and its use does not imply endorsement of or opposition to any specific organization, product, or service.

Transcript

SPEAKER_02 0:00

Hello and welcome to Thoughts on Rice, a podcast hosted by the University of California Cooperative Extension Rice Advisors. I'm one of your hosts, Sarah Marsh, and I'm a rice farm advisor for Colusa and Yolo counties.

SPEAKER_03 0:23

I'm Whitney from The Forest. I'm the Cooperative Extension Rice Advisor for Sutter, Yuba, Placer, and Sacramento counties.

SPEAKER_00 0:31

My name is Luis Espino. I'm the Rice Farming Systems Advisor for Butte and Glen counties. I'm Michelle

SPEAKER_01 0:39

Leinfelder-Miles. I'm a farm advisor in the Delta region. I work on all sorts of field crops, grains and forages, but one of those is rice. And the counties that I cover are San Joaquin, Sacramento, Viola-Solano, and Contra Costa counties.

SPEAKER_02 0:56

Together, the UCCE Rice Farm Advisors seek to provide relevant, topical, research-backed information relating to California rice production. Today, Whitney Brim-DeForest and I will be sitting down to talk about herbicide resistance in California rice. In California rice systems, a major category of resistance comprises of multiple resistance in a number of sedge and grass weeds. Rice in California is primarily grown under continuously flooded conditions and is usually in long-term rice monoculture due to soil and cultural conditions, which makes them heavily reliant on herbicides for weed control. These herbicide resistance cases tend to be due to non-target site mechanisms, or in some cases, combinations of target site and non-target site mechanisms of resistance, and present a serious challenge to growers. In fact, one of the first confirmed cases of herbicide resistance in California was in rice weeds, California arrowhead, and smallflower umbrella sedge, where benzulfuron methyl resistance was confirmed in 1993. Throughout the 90s and early 2000s, increasing numbers of weeds were reported as resistant to herbicides, with the first multiple resistance confirmed in 2000 in rice weeds in the Echinocloa species. This trend has continued through the last decades, with available methods of control dwindling. Herbicide resistance is continually quoted as a primary concern among rice producers and researchers. Due to a myriad of reasons, there are very few chemistries available for weed control in California Among these, herbicide resistance has been reported in all but the most recent, fluorpyroxifen benzyl and pyroclenil, which were made available in 2023 and 2024, respectively. Hi Whitney, good to have you on again. Thank you. Good to be here.

SPEAKER_03 3:56

or a new mode of action to a species that already had resistance every two years, you know, on average. Quite a bit. Quite a bit over the course of my career.

SPEAKER_02 4:08

Yeah, when people talk about innovation, usually they don't want to hear that the weeds are innovating ahead of the technology.

SPEAKER_03 4:13

Yeah, it's definitely, it feels like an arms race sometimes.

SPEAKER_02 4:20

In terms of rice, what are some of the most resistant and problematic weeds that we face?

SPEAKER_03 4:26

So I'd say definitely the watergrass complex, the Canicloa species. We found resistance in them quite a while ago now because it's metabolic resistance. So the plants are essentially metabolizing or eating the herbicides. They are resistant to a lot of herbicides and then also herbicides that we've never used before. And then we seem to, I don't know, select for the one that are capable of metabolizing more herbicides. So we're at a point where I think there's folks that don't have anything registered in California that currently works to control our grass species.

SPEAKER_02 5:02

Wow, that's actually kind of frightening. The chemicals that are available in California, of which I know there's relatively few, can you talk about some of the ones that have the highest proportion of resistance?

SPEAKER_03 5:14

Well, I would say that, you know, the ALS inhibitors, which would include some of our most widely used and I would say is where we first saw herbicide resistance as well so the ALS inhibitors as a group and then also now I would say propanil is becoming you know more or we have more widespread resistance to propanil we started with some of our sedges and now there's also water grass that's resistant to propanil those are probably like the groups of chemicals where we have the highest proportion but ALS inhibitors that's that's common all over the world that's not a that's not like a California specific thing propanil though that's one that I pretty unique to write systems, at least in California. So I think that we've sort of helped speed that resistance along by using that one a lot.

SPEAKER_02 5:58

Well, speaking of contributing to herbicide resistance, what are some of the common practices or environmental situations that do contribute to herbicide resistance in our rice systems?

SPEAKER_03 6:10

Well, I'd say the biggest thing is just that we have a system that is very much the same, right? So we grow rice in the same way for many, many years in the same fields. So we're not rotating crops. We're not rotating tillage systems or irrigation systems. continuously flooded rice over time for many, many, many years. And I couldn't say for certain in some cases it's been 100 years, but we've been growing rice commercially for over 100 years. So I would suspect that there are fields that we've been growing rice for a very, very long time. So the weeds just become very well adapted to those systems. So they're adapted to the environmental conditions. And then we don't have a lot of tools to use other than herbicides and water to manage the weeds. So on top of the fact that we are in the same system, we're not using a a lot of cultural controls, mechanical controls, and things like this that really help to sort of round out an integrated weed management plan. So we rely a lot on water and on herbicides. So it's not the mini little hammers, right, that we're supposed to be using. Some famous weed scientists said that, right? So we're not using very many hammers.

SPEAKER_02 7:18

So in a lot of weed management systems, crop rotation is often recommended. Why isn't crop rotation always an option in our rice systems?

SPEAKER_03 7:27

Well, so, you know, we recommend crop rotation because it allows us to use more of those tools that I was talking about. So either you're able to use different herbicides, different modes of action, or you're able to use different management tools, whether that's tillage or some other sort of cultural controls, different irrigation systems. We encourage it from an integrated weed management point of view. But in rice systems in California, I mean, part of the difficulty has been soils, right? So the soils tend to be high clay soils that don't lend themselves well to other crops in some situations. They'll become very waterlogged and other crops don't do well in those waterlogged soils. So that's one thing. But we did a study a few years ago where we talked to growers about why they don't crop rotate and why they do. So both sides. And a lot of it came down to lack of knowledge in some cases or lack of access to equipment. So we grow rice in a system that is with a lot of other rice growers. So like accessing something like a drill seeder for example might be very difficult or impossible right drill seeders are very expensive and then there's also nobody to ask like hey how do i grow this other thing because everyone around you is growing rice and so it's like it's there's some cultural constraints and then of course the environmental related to the soil and then economics right it's a risk to be able to to change to a different cropping system if you don't know the cropping system well you you know could potentially end up with no money or negative money at the end of the year right and so that you know farming is a business and so it's a it's a huge risk to undertake to to do something new that you don't know very much about and there's some other like things that came out of the study as well that it goes into a lot of detail it's very interesting very interesting to talk to people about but out of that we decided to make a crop rotation calculator um so that if people were interested there are there are a number of growers that do rotate um and so we picked some crops out of that pool that people do rotate to There's tomatoes and sunflowers, which I realize now may not be an option for everyone, but tomatoes, sunflowers, safflower, and dry beans, which were sort of the most common ones that we saw people rotating with. And they can go through, growers can go through the calculator and using their own costs or some of the costs, like they can adjust them or they come up with like sort of an assumed cost that we got from data from USDA, from several UC studies. It's all backed up by data, but they can adjust. the costs themselves as well to see if they decided to rotate to Southletter, for example, how much it would cost in year one. Would they have any benefit at all if they did? And then it gives you some options to pick like one year's worth of data or a couple of years worth of data. And it also takes into account the growers having to learn the new cropping system. So the amount of time that we interviewed quite a few growers and they gave us some value on their time and also how long they thought it would take to learn a new system. And so that's also incorporated into the calculator. So it's a tool and it's probably not perfect, but it gives people a place to start in terms of looking at, you know, if I decided to rotate the beans, would it work out for me economically?

SPEAKER_02 10:42

It's great to have that crop rotation calculator. If people are interested in crop rotation as an option, it's great to have the opportunity to get an overview of what might happen potentially before you invest all that time and money.

SPEAKER_03 10:55

Yeah, exactly. And that's why we did it. So again, it's a tool but it might help some people in making a decision. And the good thing about the tool is, too, if we want to add other crops, we could in the future. So if people were interested in looking at other things or if new crops came to the area, we could add different crops and let people choose those as well.

SPEAKER_02 11:15

And we'll have that crop rotation calculator linked in the show notes for anyone who's interested in looking at that. That was developed with Whitney Brim-DeForest, Sarah Rosenberg, and UCIPM. And it's one of the newest offerings available for those interested in crop rotation. So Whitney, there's a herbicide resistance screening program run by Dr. Kasim Al-Khatib at UC Davis. And this is a free program for our growers to bring in weeds with suspected herbicide resistance. And then Kasim will test the weeds, not only for the chemical that is suspected to have resistance, but also for the range of chemicals that we use in rice systems. Can you give me a bit of background about this program and how long it's been going on?

SPEAKER_03 11:56

Sure. So the program was started with Dr. Albert Fisher. And I believe it was, I'm probably going to get the year wrong, but back in the, maybe the mid 2000s. And it started with testing water grass species. And that's because that was one of the first, most important, you know, species that we found resistance in, widespread resistance. And it was metabolic resistance. So they were needing to know, you know, if, okay, if thiobin carb works, for example, but serrano doesn't or chlomazone doesn't, like what are my other options? So that's why the program really started. And it was pretty small at first, and then it's grown over time. Now I believe we take all the weed species. So any California rice weed species, or only rice though. So only California rice weed species. And growers or PCAs can submit in the fall, and then they should get the results back in the spring. And usually it comes with a report that says, you know, okay, these are the options that are registered in California rice. These are the ones that don't work on your weeds and then these are the ones that might still work and it's very helpful to use as a tool I use it as a tool when I sit down with growers and PCAs I say you know did you get your seed tested and then we try to go through and plan out a program based on those results so it can be very very helpful for planning especially when you have a field that's really it seems to be very tough weed wise it can give you some options that you might not have known that you had so It's a very, I think it's a very important program. If people don't know how to collect weed seeds, the Rice Farm Advisors were here. We can help you collect. It is really important to collect weed seeds well if you're going to do this program. When I was there, when I was a grad student, there was some contaminated stuff. There was stuff that wouldn't germinate for a variety of reasons. So if you are going to submit, you want to make sure you go out into the field and shake the weed seeds. Don't strip them. off the plants. So shake them into a bag and whatever falls into that bag should be good and should germinate. So that's really important. And you want to make sure you get seed from all over the field, wherever you think there's a resistance, not just on the edges. So sometimes the edges, we've got things happening, or maybe there's like a strip down the field that is a skip. You don't want to collect from that. You want to make sure you get, you know, good distribution across the field. So if we're, if we're available to, you know, To help, we're happy to do so. And please give us a call. We would love to come out and help collect weed seeds.

SPEAKER_02 14:33

So Whitney, for those who aren't aware of this program or how to submit after they collect the weed seeds into the bag, what did they do with them then? Oh,

SPEAKER_03 14:41

good question. So there's a form on our UC Rice website that you need to fill out. And then they can either drop them off at their nearest farm advisor office or they can take them up to the Rice Experiment Station in Biggs and they will accept them there. So either way.

SPEAKER_02 14:55

Great. Thanks for that clarification. Sometimes we get calls about suspected herbicide resistance, but when the weeds get tested for resistance, our testing says that they're actually susceptible to the chemical. Can you explain a little bit about why that might happen?

SPEAKER_03 15:11

So sometimes it could be that the collection wasn't very good, right? So you collected out of a part of the field that actually was still susceptible. So that could be. It could also be that when you made the application, perhaps it wasn't quite at the right timing. So we see this a lot with serrano and or clomazone and sprangletop clomazone usually is applied day of seeding and sprangletop tends to emerge not very quickly under flooded systems and so sometimes you apply clomazone and then it's actually dissipated by the time the sprangletop emerges in the field so it's not that it's resistant it's just that the timing of the clomazone totally missed when the sprangletop was was was in the field so they're they're not there at the same time so it's not going to control the weed so that can happen a lot timing It could also be that there was a misapplication of some sort. You know, I've made mistakes myself when I'm putting on applications of things or I left something out. So you can sometimes deduce that from like looking at what else was controlled in the field. And if you're seeing several things that should have been controlled and they weren't controlled, that might be a clue. Water management can be another one. So if you're putting out a granular product and you're not holding the water for the recommended amount of time, it's not going to do what it should do most of the time. So a lot of our herbicides won't persist if you drop the water. So you drop the water and your efficacy is gone. So that's why that water hold period is not just for water quality issues. It's also for herbicide efficacy. So it's really important to hold the water for the recommended amount of time. On the flip side, it could also be that like you were putting out a foliar product, a liquid spray, and you didn't drop the water. And so the weeds weren't actually exposed. So you need for foliar applications, you need the weeds to be out of the water. Otherwise, you're just spraying the water and it's not actually making contact with the leaves. So there's numerous ways that herbicide application can go wrong. And I'm very guilty of many of these myself. It's so easy to make a mistake. You can also put on the wrong amount that happens, right? Miscalculation. You can put it on with a nozzle that's clogged and then you end up with a skip down the field. You can improperly calibrate. And so you think you're putting it on a certain rate and it's not the rate you put it on at. If it's biplane, you can be too high, right? So there's a number of things that can go wrong. So if you think you have resistance, please do call us out. We can kind of help based on the pattern we see in the field, based on what else is controlled. We can recommend, hey, yeah, it's a good idea to get this tested. And then the herbicide resistance testing program can help you figure out whether or not it is susceptible or resistant.

SPEAKER_02 17:56

We don't have a ton of chemicals available in California rice systems for herbicide management. That's just kind of a fact, especially in comparison with the rest of the U.S. How can we steward the chemicals that are available in order to maintain the use of them in our system?

SPEAKER_03 18:10

You know, some of the things that I've been saying, so making sure that you have the right rate at the right timing, those things are really important. So when you're putting things on at the wrong rate or the wrong timing, you can put on less than it should be applied. And when you're constantly going under the label rate or the recommended rate, it will select for resistance more easily. So you want to make sure you have the right timing, the right rate, and then also making sure that you're rotating your chemicals. So rotating modes of action from year to year. And also I say this a lot, but within season too. So like say you're always ending up with propanil as your last application, that's going to make it so that we're... for propanol resistance some things, right? So maybe you're rotating your chemicals at the beginning of the season, but then you're always following up with propanol. So eventually, yeah, you're going to select for propanol resistance. It's just going to happen. So rotating both within seasons and between seasons and also with your different timings. So if you're putting on thiobin carb at the beginning of the season, next year you should put on something else at the beginning of the season if you can. So it is hard to do and I'm not denying the fact that it's difficult and there's a lot of rules and regulations that make it really hard. But there's also some other tools that you can use, like maybe rotating a stale seed bed one time. We've had growers do that. So like taking a field, doing a stale seed bed in one field that kind of cleans up the field and resets it. If you can crop rotate, that can also be a good tool to rotate out for a year. Fallowing. So if you have a really bad field and you've got to sell your water one year or need to sell your water, can't use your water, you know, fallow the worst fields. So the ones that have the worst weeds, those are the ones you should follow. So again, I realize it's difficult, but stewarding the chemicals is really, really important because like Sarah said, it's really hard for us to get new chemicals for a variety of reasons. It's not just for registration or because of registration. It's also just because there are fewer and fewer chemicals out there to find. And then the ones that work, there's even fewer, right? So we need them to not kill the rice and kill the weeds And so it's just, it's a very small pool of chemicals. And so we're always working on registering new things and finding new things. But a lot of the stuff that we test just doesn't work for a variety of reasons. Again, we want to keep the chemicals that we have for as long as possible.

SPEAKER_02 20:44

Whitney, thanks for taking the time. So at the time this episode will come out, it'll be about mid-August. Is there anything we should be on the lookout for?

SPEAKER_03 20:53

Actually, so yeah, mid-August is a perfect time to be scouting for herbicide resistance not all the weed species will be ready to harvest at that point in time or ready to collect seeds but again we can go out and we can help you so typically the water grasses might be a little bit closer to harvest time but things like sedges might be ready at that point be scouting for herbicide resistance and starting to collect seed

SPEAKER_02 21:17

great thanks Whitney

SPEAKER_03 21:19

thank you music music

SPEAKER_02 21:32

Our next upcoming event is the Rice Pest Management Course, which will take place on September 4th at the Rice Experiment Station in Biggs, California. Please note that registration is required for this event, and the registration link will be in our show notes. Please note, the registration will officially close on August 30th. I cannot stress this enough. August 30th is the last day for registration, so if you're planning on attending this event, please Please go to the link in our show notes and register. We hope to see you there. The event will start at 8 o'clock and go until 3 and will consist of weed identification, workshops, talks about pest management and rice, and field tours. If you're interested in learning more about our program, please check out our other resources, which will all be linked in the show notes. The UC Rice blog, the UC Agronomy Rice website, and our newsletters, which are Rice Brief which covers Colusa Yolo, Rice Notes, which covers Yuba Sutter, Rice Leaf, which covers Butte and Glen, and Rice in the Delta, which covers the rice-specific practices to the Delta region of California. Thanks for listening, and as the growers always say, have a rice life. Mention of an agrochemical does not constitute a recommendation, merely the sharing of research findings. Always follow the label. The label is the law. Find out more at ipm.ucanr.edu. The views, thoughts, and opinions expressed are the speaker's own and do not represent the views, thoughts, and opinions of the University of California. The material and information presented here is for general purposes only. The University of California names and all forms, and abbreviations are the property of its owner and its use does not imply endorsement of or opposition to any specific organization, product, or service.