Weedy rice with Whitney Brim-Deforest

Feedback Poll   


Today Whitney Brim-Deforest and Sarah Marsh will be sitting down to talk about weedy rice in California. Weedy rice is the same species as cultivated rice, Oryza sativa, which contributes to the difficulty in controlling it; any herbicide that would kill weedy rice would also hurt the crop. Weedy traits of weedy rice including seed shattering and long dormancy. What that means is that the seeds fall off the panicle really easily and can remain dormant in the soil seedbank for years before germinating.

Upcoming Events!

• Annual Rice Field Day on August 28
• Rice Pest Management Course on September 4 *registration required*

Weedy Rice Resources
Weedy Rice website
Rice Production Manual - Weed Section
Subscribe to the Weedy Rice Mailing List HERE

Other Resources

UC Rice Blog

UC Agronomy - Rice

Rice Briefs (Colusa/Yolo)

Rice Notes (Yuba-Sutter)

Rice Leaf (Butte/Glenn)

Rice in the Delta


Mention of an agrichemical 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" 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_01 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 Yolo and Colusa counties.

SPEAKER_00 0:26

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

SPEAKER_02 0:34

My name is Luis Espino. I'm the Rice Farming Systems Advisor for Butte and Glen counties. I'm Michelle 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, Yolo-Solano, and Contra Costa counties.

SPEAKER_01 0:59

Together, the UCC rice farm advisors seek to provide relevant, topical, research-backed information relating to California rice production. Today, Whitney BrimdeForest and I will be sitting down to talk about weedy rice in California. Weedy rice is the same species as cultivated rice, Ariza sativa, which contributes to the difficulty in controlling it. Any herbicide that would kill weedy rice would also hurt the crop. Weedy traits of weedy rice include seed shattering and long dormancy. What that means is that the seeds fall off the panicle really easily and can remain dormant in the soil seed bank for years before germinating. Whitney has been studying weedy rice populations in California for several years and has been compiling some of the most comprehensive information relating to California weedy rice populations. Whitney Brim de Forest has been a rice farm advisor in the northern Sacramento Valley for about eight years, but she's been working in rice and in this area for far longer than that. She earned a master's in international ag development and a PhD in horticulture and agronomy from UC Davis, where she worked in weed science research in flooded rice conditions and managed field trials for the UC Davis Weed Science Group. She has been working in weed management and herbicide resistance, as well as collaborating with other farm advisors in agronomy and rice research. can you give us some background on this weed

SPEAKER_00 3:17

sure so weedy rice is considered i would say probably the worst weed of rice worldwide and the reason it's such a bad weed is that it is the same species as rice so you're essentially you have rice infesting rice which makes it very difficult to manage from many different standpoints from identification to you know what can we use to to uh control it so it's just a really strange weed i guess in terms of weeds. You

SPEAKER_01 3:44

mentioned that it's the same species as rice. How do people usually tell the difference in the field between weedy rice and rice that's a cultivated crop?

SPEAKER_00 3:53

So in our system, we've been, I guess, kind of fortunate in that all of our weedy rice types look relatively similar. So they tend to be taller than our rice crop, taller than the medium grain varieties at least. And then they're pubescent, so they have like rough leaves. Again, it's, you be a characteristic of some of our varieties. So it's not always something you can use to distinguish, but usually taller, lighter in color, and pubescent. And that's before it heads out. Once it heads, it's quite a bit easier to distinguish from our rice varieties. Most of the types we have look very different, for the most part, from our rice varieties. It's difficult to spot. I'll just say that. It's not the easiest thing to spot in the field.

SPEAKER_01 4:40

So what does the geographic distribution of weedy rice in California look like?

SPEAKER_00 4:45

So it's been found in every single one of our rice growing counties. So all the way down to San Joaquin, actually. So it's, you know, I would say at this point in time, pretty widely distributed. We do have certain types that are more prevalent than others. But yeah, it's prevalent in every county.

SPEAKER_01 5:06

And as far as the different rice farming systems in California, continually flooded versus drill seeded versus organic, Is it found in all of the systems of rice farming that we have in California?

SPEAKER_00 5:17

It is, but flooding does suppress the germination. So it definitely comes up less under our continuously flooded systems as opposed to like a drill or dry seeded system. So if you're trying to, you know, minimize the amount of weedy rice you have in your field, continuously flooded is the way to go. In terms of organic versus not, all the fields that I've seen, it's pretty much equally distributed. So in terms of when we

SPEAKER_01 6:03

see weedy rice in the field, is there a certain number of plants per square foot that leads to a level of economic injury?

SPEAKER_00 6:10

So we don't really have good data on that. in terms of being in the field, but when we get the greenhouse studies that we've done have shown that when you get up around, I believe it's about 40 plants per square foot, you really see the yield drop off. And that's really because the weedy rice is competing directly with the rice. And it tends to be a very large plant. It tillers a lot. Some of the weedy rice types are tillering like 40, I think we've seen some that have even like 100 tillers per plant. So there these massive plants. And so once they get in really high densities, um, most of the seed that they have is shattering onto the soil and the rice says the regular varieties are really outcompeted. So yes, there is, we do have a, you know, we do have yield decreases, but I would say like field wise, I'm not sure I could say that specifically, but yes, for the greenhouse for sure.

SPEAKER_01 7:04

It sounds like weedy rice is a really highly competitive weed, especially in our system.

SPEAKER_00 7:09

Yes. Very highly competitive. Um, and it persists for quite a while. Most of our types have very high dormancy. So that means when the seeds are in the soil, they're not going to germinate unless like everything is right. And so they can persist in the soil for a very long time. And this is anecdotal, but we have growers that have woody rice that's been in the field for 20 some odd years here in California. And I think from other parts of the country, they've done research that shows like, you know, 10 plus years, some of the seeds have persisted in the soil. So unfortunately, we don't have that exact data for California, but we do know just, again, anecdotally that some of the fields, they've been dealing with it for 20 or so years. But that's not all the types, thankfully. So some of the types have less dormancy, and those ones are a little bit easier to get rid of than the high dormancy types.

SPEAKER_01 8:01

So if you've got seeds that can last in the soil seed bed for so long, it seems like management strategies such as tillage would actually not be very useful. Is there other management strategies that you can use in season to help with weedy rights?

SPEAKER_00 8:16

So at this point in time, we don't have a lot of things that we can use in season. We have been recommending that people rogue or hand pull plants out of the field. That's one of the best techniques still. If your plants have headed, though, the problem with that is, is like hand pulling plants that have seeds that are shattering as you go out of the field is not a great idea. So the other thing we recommend is if the plants have already headed that you just go cut the heads off into like a bucket. Again, this is not a good strategy if you have a lot of plants, but most of our fields are pretty low infestation levels. So I think for a lot of growers, they can get away with just hand pulling or cutting heads off. We do have one herbicide that's allowed to be sprayed that's suppressed. It's capric or caprylic acid is the active ingredient. And that has to be applied at like the highest rate and the water has to be out of the field when it's applied so it's not practical in every situation um but it is currently the only option that we have and there can it's a it's a contact herbicide so if if uh if you don't completely kill the plants it's not gonna you know stay there and if the plant you know puts out more parts or something doesn't get completely killed it's not gonna be there to control the weedy rice forever so it really is just like you know you spray the one time if you miss part of the plant or if the plant keeps growing through it it's It's not 100% effective. So we're working on other herbicides still, but nothing else yet at this point. So yeah, really, it's just roging, cutting heads off, or spot spraying if you can.

SPEAKER_01 9:55

Not a lot of options for in-season management.

SPEAKER_00 9:57

Not a lot.

SPEAKER_01 9:59

What about post-harvest or pre-plant? Is there any different methods that growers can try to take to remove weedy rice or prevent it from being in their fields in the first place?

SPEAKER_00 10:08

Well, so I would say like one of the most important things that the rice industry we did was to pass a law basically that everyone has to use either a certified seed or a seed that's gone through a quality assurance program. So that certified would be for like all of our medium grain varieties. This quality assurance program is for some of the specialty varieties, but that means that someone's been there in the seed field inspecting it for weedy rice and there's zero tolerance for weedy rice in seed fields. So that would be the first most important thing, certified seed, which everyone should be planting now. are using now. So at harvest, we recommend not using a stripper header just because it can sort of spray seed everywhere. And so if you have weedy rice in the field, it's more likely to shatter it off. So you really want to get it out of the field, even if it's into the combine. You want it out. So that'd be the first thing. After you've harvested, try not to till as much as possible. You want that weedy rice seed to stay on the soil surface. If you can, you could burn, but we're not sure of the efficacy of burning actually on killing the rice seed. So that's, but we still recommend it could kill those seeds. So it's recommended. Burn if you can, don't till, and then flood the field for as long as you can. And that encourages predation by birds. It also encourages the seed to rot in the field. And I think most of the growers that have been doing those things have found that it has reduced the amount of weedy rice in the field. I don't know if it's eradicated it completely, but reduced it at least. And then in the spring, Again, if you have a way to not till, great. But if you can or if you need to till, then you can do something like a stale seedbed if it's a really bad infestation. So then you would flush the field, bring up hopefully the weedy rice or a lot of it, and then spray it with glyphosate or some other non-selective herbicide. So that's kind of like all of the control techniques that we have for weedy rice, which is not a huge arsenal of tools. It works. I think it's been working. We've been seeing reductions in people's fields. And then if people can, we've been noticing that following actually seems to be helping to reduce weedy rice seed in the seed bank. So we did a study in Davis a few years ago that showed that over time, over about three-year period, we were able to get rid of most of the weedy rice in the field just by following.

SPEAKER_01 12:36

That's really interesting. And as far as post-harvest management techniques that you talked about, a lot of the Actually, in my experience, the growers are actually already doing some or most of these techniques. So it seems like if you do have a problem, it's relatively easy to get the equipment and the know-how to incorporate even more of these management problems into the system.

SPEAKER_00 12:59

Yeah, I think so. And then I guess the other thing that I didn't say was just making sure that people are monitoring for weedy rice. So that's a really important one. If you don't see it and don't know that you have it, I think that's the easiest way for it to propagate. And then I guess also I forgot to mention equipment. So if you do have a field that's infested with weedy rice, you want to make sure that you're not using your equipment in that field first and then taking into other fields. But that applies to, I would say, pest management generally. But we've really tried to emphasize this with weedy rice spread. I think one of the main ways that we've seen spread is through equipment. I can't 100% say that for sure, but that's one of the things I've noticed is people either sharing equipment with each other, using custom you know, operations and maybe even planes, but making sure that we're cleaning out in between operations is really, really, really important.

SPEAKER_01 13:51

Let's switch gears a little bit and talk about the different biotypes of weedy rice. I understand that a part of your research program has been identifying different types of weedy rice. So can you tell me a little bit about how long you've been working on identifying the different types of weedy rice?

SPEAKER_00 14:08

Sure. So I guess back in the early 2000s, That was the first sort of weedy rice official find, I guess, where people started tracking it. That was not me that found that, but some of the other farm advisors at the time. And then in 2016, we started to see like a bunch of reports the previous year of different things that we thought were off types at first. But then we did some research in the greenhouse to look at their shattering and dormancy, compared them to weedy rices from other places. and also did a genetic test at the time. And we were able to see like, you know, we had approximately five types at that time in 2016. And then over the past like eight or so years, I guess now, we've continued to collect samples that seemed like they might be weedy. And then the past couple of years, we did a second screening with a bunch of new types or new samples that we found to look again at shattering and dormancy. And now I guess we're probably up to Wow. And I

SPEAKER_01 15:15

guess, is that eight or nine types and counting? Or do you think that's probably it?

SPEAKER_00 15:42

tend to outcross at much higher rates. So the longer we have weedy rice or weedy types in the field, the more possibility we have that they will cross and create new types. And so back when we did our genetic testing back in 2016 and 17, we found there was already a lot of crossing happening. So none of the types were purely, you know, any quote-unquote type. They were all mixtures with other things, whether that was varieties or a couple weedy rice types that had crossed with each other. there was a lot of genetic variation. So basically, you know, the longer we have weedy rice out in the field or weedy types, or even off types, I'd say, or things that shouldn't be there, the greater the possibility is that we'll end up with more types.

SPEAKER_01 16:27

Can you tell me a bit about why it's important to understand the differences in the weedy rice biotypes?

SPEAKER_00 16:32

Yeah, so basically, we wanted people first to be able to ID them. So we focus a lot on looking at phenotypic characteristics like seed size, and seed color and things like that, on length or whether they have ons or not. But really and truly, it's because that phenotype, like how they look on the outside, comes with a set of traits. And so that set of traits, the most important thing is whether or not they have red pericarp. Possibly the second most important thing would be their dormancy level. So that helps inform our management strategy. So if you have a type that's really low in dormancy, meaning that it germinate very easily, we've seen that basically just switching a certified seed is a huge help. So you switch a certified seed, that seed that was there before is not going to persist in the soil for very long, and in a few years you should pretty much be free of woody rice. Whereas the high dormancy types, like say type 3 and type 1, those types persist for a very long time and take a much more involved management strategy to really get rid of those types. They'll stay there and, you know, if a grower thought they got rid of it or mostly eradicated it, but then they move soil in the field, sometimes we'll see a pop-up in another spot that they hadn't had it before. So it might have just been, you know, under the soil waiting until the soil got moved again. So it's really, yeah, being able to ID the types is important for management.

SPEAKER_01 18:05

Can you talk about any future research that you have with weedy rice?

SPEAKER_00 18:09

Sure. So, I mean, we're doing some research right now looking at the newer biotypes that we found. So we should have more extension information coming about how to ID them, you know, if they have high or low dormancy, their seed color, et cetera. And then we're also probably going to do another genetic analysis to see if with the new types, like where are they coming from? Are they related to the old types? Are we bringing in stuff again from other places? So those are two studies that are in process. We're still looking at some herbicide work, trying to find spot sprays. The Rice Commission is working on that extensively with our flora program. We've been working on that for a few years, hoping, keeping our fingers crossed, that we will have a spot spray herbicide. And then we've been doing some testing in the field with oxyflorafen, which we hope will come to California rice at some point in the near future to see if it works to control weedy rice in California. It does work in the South. It's been shown to work a bit. So we would like to see if it works on our types here. Some of the greenhouse work shows that it does work, but we need to do field testing still to make it 100% certain. So those are, I'd say, sort of the most important studies that we're working on right now. But we're always open to doing more research if people have suggestions or things that they'd like to know more about.

SPEAKER_01 19:33

And with that, can you tell me where people can go to find more information about weedy rice?

SPEAKER_00 19:38

Yes. So we actually have a weedy rice website. So it's caweedyrice.com. And it was put together with UC folks and the California Rice Commission. And that's the repository of all things related to weedy rice. I think there's a little bit on our UC rice website as well. But yeah, the main source is from that California weedy rice website. We also do have a mailing list, an email list that you can sign up for if you'd like to be aware of field days or other things that are related specifically to weedy rice.

SPEAKER_01 20:11

Whitney, thanks for providing this information about weedy rice. At the time of recording, it's the beginning of August. Do you have any thoughts or notes to put out about what we've seen in the rice season this year and what to expect coming up?

SPEAKER_00 20:25

Well, I guess I will just say that now is the time to scout for weedy rice. So if you're looking out in your fields, now would be the time that you would see it. So you should have put on all of your herbicide applications by now. And if there's something strange looking out in the field, please give us a call and we'll be able to help you out and see if it's weedy rice or maybe it's just something else. But please give us a call if you see something that looks odd. Great. Thanks, Whitney. Thank you. Thank you.

SPEAKER_01 21:05

We have a few upcoming events on our docket. The annual Rice Field Day will take place on August 28th at the Rice Experiment Station in Biggs, California. The event will start promptly at 8 and go until noon, and will consist of field tours, talks from the rice breeders, and a delicious lunch. No registration is required for this event. 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 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 Briefs, 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.