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Thoughts on Rice
This podcast is for growers, PCAs, consultants, and other industry professionals in the California rice industry. We'll primarily be focusing on the Sacramento Valley and Delta Region of California. The UCCE Rice Farm Advisors aim to deliver extension information relating to the California rice industry.
Find out more about UCCE and California rice here!
Thoughts on Rice
First Peak of Armyworms with Luis Espino
Sarah and Luis discuss armyworms as a significant pest in California rice production. The discussion included Luis providing current updates on armyworm populations, scouting techniques, treatment thresholds, and management options for rice farmers.
Upcoming Events
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Armyworm Resources
Second Peak of Armyworm Podcast Episode
Other Resources
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.
UC ANR is an equal opportunity provider and employer
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 Marchionish, and I'm a rice farm advisor for Colusa and Yolo counties.
SPEAKER_00:I'm Whitney from DeForest. I'm the Cooperative Extension Rice Advisor for Sutter, Yuba, Placer, and Sacramento counties.
SPEAKER_03:My name is Luis Espino. I'm the Rice Farming Systems Advisor for Butte
SPEAKER_01:and Glynn 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_02:Together, the UCCE Rice Farm Advisors seek to provide relevant topical research-packed information relating to California rice production. As of recording, it is officially the beginning of July. And so kind of on theme with that, we're sitting down with Louisa Spino to talk about the fate of armyworms in rice as we're approaching the first peak of armyworm population in the 2025 rice season. Last year, we had a podcast episode devoted to the second peak of armyworm infestation. So if you're interested in hearing more about that, you can go find that in our back catalog. The armyworm is an insect commonly found in rice fields, and it becomes a pest when populations reach high densities. Prior to 2015, we hadn't had record of high effects of armyworm defoliation in rice. However, a serious armyworm outbreak occurred in 2015, resulting in yield reductions of up to 20% in some fields. After 2015, research efforts focused on controlling this armyworm and actually led to the registration of a chemical being able to be used for control of this pest. Now, infestation pressure fluctuates throughout the years, and it's hard to tell if a year is going to be a heavy armyworm year prior to it actually showing some damage. But it's important to remain vigilant, especially at this time of year. And first and foremost, always scout the fields, keep an eye out, and see if there's any worms or severe defoliation in the field.
UNKNOWN:Music
SPEAKER_02:Luis, thanks for being here today. Hi,
SPEAKER_03:Sarah.
SPEAKER_02:Now I'm here to talk to you about pretty much everyone's favorite mid-season pest, which is the armyworm. As a recording, it's the beginning of July, and so this is kind of about the time we want to be, well, we're kind of past the time of starting to think about armyworms, but now's when we should be really starting to focus on it, right?
SPEAKER_03:Right. Yeah, we're probably just on the other side of the armyworm, the larval peak. So actually this morning we were counting worms on a trial. And we started, this is our one week count. So we did counts at three days and then a week ago. And yeah, our numbers went up quite a bit from our first count on the untreated. But I'm guessing, you know, given the size of the worms, they're going, they're starting to pupate. So they're probably going to, the numbers are going to start going down now.
SPEAKER_02:Pretty low. large worms then that you were seeing?
SPEAKER_03:Pretty large, yes.
SPEAKER_02:And the worms that you were seeing, for the most part, they were all armyworm. They weren't fall armyworm. They were our traditional true armyworm.
SPEAKER_03:Right, yeah. We don't have fall armyworm. It is the true armyworm, the one that we always see on rice. Occasionally, we can also see western yellow striped armyworm, but the When I have seen the Western yellow stripe, it has always been on the duck salad or maybe on the red stem and is eating those weeds, but not the rice. So it likes to eat the broadleaf weeds and not rice. And so, yeah, I think, you know, in the past, we always said that both were a pest of rice, at least in the past, you know, 15 years. It's only been the true army.
SPEAKER_02:That's good. Okay. So maybe we should be promoting Western yellow striped army worms. I
SPEAKER_03:wouldn't do that. No, but they can. They're an army worm too. So they have that same behavior where they move in mass into areas where they can feed on. And I've seen them move into alfalfa fields, for example, a few years ago. And so, yeah, I don't know if they were to have an outbreak like that and they were to move into rice, they might feed on the rice. Sometimes, you know, insects, if there's nothing left, nothing else they can eat, they might eat whatever's available and they might eat the rice. but so far I haven't seen them eating rice.
SPEAKER_02:Well, let's hope it stays that way. As far as what you've been seeing, you mentioned a trial that you were working on earlier today. And I'll tell you, I've been out and about a little bit and the rice experiment station and some fields I've been in lately, I've been seeing not a lot of defoliation, but a lot of inch or smaller sized worms. Does that kind of concur with what you've been seeing?
SPEAKER_03:Yeah. So yes, we've, We've seen this year certainly more worms than the past two or three years. And it's not outbreak levels. And it is spotty. Some fields you see large numbers, other fields you don't see very many. There could be a little bit of a difference between areas. So we have one of these fields that we monitor constantly in Ridgevale. And over there, we saw worms very early on and they reached, you know, they were pretty large. By now they're probably gone. Well, that field had to be sprayed because defoliation was pretty uh, it wasn't a threshold level, but it was really approaching threshold level. Uh, so yeah, those worms were a little bigger. So, you know, then we're another, or the, one of the fields that we monitor, we ended up setting up a trial there and those worms were a little behind, but now they're cycling, you know, they're getting to the point that there will be cycling out.
SPEAKER_02:And then kind of touching on that, um, because you mentioned a lot of the different sites that you're, uh, tracking these numbers in as part of the armyworm monitoring network is that right
SPEAKER_03:yeah so yes the monitoring network so we use the pheromone traps and and we have these 15 sites and we check them every week and then we we look at the number of moths that we're catching in the traps and so you know we've done this for several years now maybe we're approaching maybe eight nine years And so we've learned that you know, the number of moths really doesn't give us much information. Some years we find huge number of moths in the traps, but then there's no worms in the field. And we can talk about why later. But we've learned that what really gives us the most important information is when we reach the peak of moths in the traps. And so when we reach that peak, we know that That week and the following week is when we're going to see the peak number of worms of larvae in the field. And so, you know, when you have high numbers of worms, those are the ones that are going to be defoliating and potentially causing damage. And that's when it's going to be easier to find them. So that's how we recommend using the traps or the information from the traps is once you identify, okay, we're at peak or we reached the peak last week because we check it every week. So we know the peak happened last week. Then that's the time to really monitor closely, look for worms. And if needed, you know, a treatment can be made.
SPEAKER_02:Yeah. So I guess kind of to distill it down, the traps are a really good way of seeing if there's a presence of moths, but not necessarily the number of worms that might be in the field.
SPEAKER_03:Right. Yeah. So what we've seen is that the number of worms varies, like every field is different. So say we find 50 moths a night in field A, 50 moths a night in that field may mean two worms per square foot but on field b 50 moths a night might mean eight worms per square foot so it changes so we can make a recommendation based on the number of moths because of that so now why is that The pheromone we use for the armyworm traps, for the moth traps, is a pheromone that attracts males. And so the males will mate with the females, and the females then lay their eggs. But we're not catching the females, which are the ones that will carry eggs. Now, this is interesting. Now, we know in nature that the ratio of male-female is 1 to 1. So in theory, if there's 100 males, flying around. There should be 100 females flying around. So these army worms, they are migratory. And so they move, you know, across the landscape. I suspect that they move into our area coming from probably from Southern California, maybe other areas south of us. And they move into our area and then they will continue moving north and go all the way to Canada. And so what happens and there's a there's a recent paper that was published this year, actually, where they from some workers in Quebec in Canada. And so they were trapping army worms using light traps. The light traps should attract males and females equally, but they were getting more males than females. And so what they have been able to deduct from that information is that the movement of moths is not one-to-one. So the males will move and they will fly while the females might be migrating, but then they might need to stop if they're ready to fly. lay eggs. So they might stop in some areas to mate, lay eggs, but the males will, you know, will continue moving. And so that difference seems to be why some years, you know, we might get a lot of moths, you know, a lot of male moths, but then there's no worms. It's because, you know, there's not enough females out there. There's very few females. When I say few, I'm the number of females that would cause an outbreak, right? So that's, I think that kind of solves that mystery that, so why are we not, even though we catch so many moths, why are we not seeing worms in the field? And it might be related to that. So that, I really enjoyed reading that paper.
SPEAKER_02:That sounds like a really interesting paper. We'll be sure to link to that in the show notes for anybody who wants to read that further.
SPEAKER_03:It's a paper from Lemire Hamel. That's the last name of the main author and it's on the Canadian entomologist. in 2025. So anyway.
SPEAKER_02:Could it be, is it that there are fewer females or just that the females are less mobile?
SPEAKER_03:Well, I'll have to go back and read, but I think there's fewer females arriving at certain locations when they're migrating. And once the females go into reproductive mode, they might not move as much because they have to conserve energy to produce eggs. And so they might not fly as long or, you know, as the distances that the males do, because the males don't need to save energy.
SPEAKER_02:No, they're kind of done doing their part. They just need to fly.
SPEAKER_03:Right. They just fly, you know, and hope that the females are around when they get where they're going. Right. Yes.
SPEAKER_02:Well, that's really neat. I mean, like you said, potentially a mystery cracked at least a little bit to see maybe something worthy of more investigation.
SPEAKER_03:Right. It makes sense. And that this kind of explains why we don't always see huge populations even though we see a lot of a lot of moths
SPEAKER_02:well okay i'm kind of going back to this tracking network i'm looking at it here and it looks like across the area where we do the monitoring it looks like some of the trap areas haven't hit their peak moth captures as of last week some of them are approximately at peak and then some of them saw their peak a couple of weeks ago even i mean do we have an explanation for that or is that just all part of the variability we see?
SPEAKER_03:So I think there's variability. So within a field, sometimes, you know, in each field that we monitor with the traps, we have three traps. And so even within a field, some traps, you know, peak maybe a week earlier than other traps. So there is some spatial variability, you know, even at the trap level. But I think that there might be also some differences in geographic area areas. So like I was saying earlier, we have this field in Richvale where we saw early on maybe a little bit more activity on the worms versus other fields, not a little bit to the east, not still in the area, but, you know, closer to bigs. And this other field was a little behind. So there, I think there might be some geographic differences. Now, why? I don't, I can't, you know, I can't say what makes one field different than another. And it's the same reason why some fields tend to see high numbers versus other fields don't seem to have a lot of worms in them. I don't know what the reason is, but there are some differences like that. So important to, you know, scout Pay attention to, you know, if there's information from the area, you can pay attention to that. But I think in general, the average that we send out with the email, you know, with the updates on the trapping, the average, what we send is the average for the whole valley. And that gives a good idea of, you know, where the populations are.
SPEAKER_02:Well, you mentioned scouting. Let's kind of get into that a little bit. Do you have recommended techniques for What time of day to scout? What area of the field or the basin to scout? Anything you want to touch on here?
SPEAKER_03:Well, so, you know, the scouting is you got to look for defoliation, but also you got to look to see if there's worms, right? You don't want to see defoliation, but maybe the worms already cycled out. So, you know, let's say you come back from 4th of July weekend next week and you might see some defoliation, but the worms might have already cycled out. cycled out so there's no point in doing any treatment so look for worms you know look at the base of the canopy the worms like to hide especially in places where there's thick rice and they like to be parallel to the tillers and so those thick areas that's where they're hiding you know I know some growers like to shake the rice and see how many fall in the water and that works too you know but you might miss the ones that are right at the base of at the water level you know just just hiding there in the tillers and usually we see higher densities in the borders it seems like that's where the infestation starts so if you're scouting you know you can check those areas to see how it's doing but always take a look further you know walk a little bit into the field because there might not be that many once you go you know 40 50 feet into the field. So I think that would be what I recommend. The other thing, sometimes I get the question, because the threshold is by defoliation. So we want to avoid getting to higher than 25% defoliation, which is a little tricky. What is 25%? You just kind of got to, you have to guesstimate. You can also count the worms, right? And a lot of people do that. It gives you another parameter. So a few years ago, we did a study where we were counting worms and trying to correlate that to defoliation level. And whenever we had more than six armyworms per square foot, then we would start seeing defoliation that was close to 25%. So that's an informal threshold, you know, because we did it, but we didn't have enough samples. with high levels of defoliation. This year would have been a good year to do that, but we were not planning on doing it. But if you're seeing more than six, certainly if you're seeing more than 10, then that's concerning. And either keep a really close eye on the rise, or if you're seeing some important defoliation, then maybe consider a treatment. This year is tough with the prices, But you can wait. So that's the other thing is, you know, you can wait. One of the insecticides that we have registered, methoxyphenazide, that's a good job of controlling the armyworm quickly. So, you know, you spray and it's not going to be immediate, but, you know, at three days, you'll see a good reduction. A week later, you will see more than 90% control. So that's the good thing about having a good product that works is that, you know, you can wait. until you are actually sure that you, you know, you need to treat. You want to avoid, you know, those preventive applications that sometimes, because we had, you know, with pyrethroids that were not working very well, some people were trying, well, maybe if we put it early, we'll get those little ones, but you don't know if you're really going to need a treatment or not. So we want to get away from that.
SPEAKER_02:Yeah, not just spraying because you think you might need it, actually spraying when it's economical and most effective against the pest and using a product that can do that
SPEAKER_03:right and we have a product that can do that so that's that's
SPEAKER_02:good rice is really pretty tolerant of defoliation i mean especially at this stage right this first peak of army worms is that i mean if even if you've got 10 15 defoliation is there going to be an effect on yield later on the season
SPEAKER_03:now we've we've done so we've done trials where we kept we defoliated rice now we We did it artificially because we couldn't have, you know.
SPEAKER_02:You couldn't raise army worms to graze your rice. Yeah.
SPEAKER_03:It's hard to find places where you could have different defoliation levels. So we defoliated rice. We, you know, we just use scissors and we did it across several days to try to mimic how the army worm does it. And if we lose, if we lose 25% of the foliage, we don't see a yield reduction. But if we lose 50%, then we start seeing a percent reduction. And when we did it, we did it for three years. I think on average, we were losing 4% of yield when we defoliated 50%. So if you imagine a field that's eaten half you will lose, or an area that's eaten half, you will lose about, you know, if the field produces 100 sacks, you're losing four sacks.
SPEAKER_02:Which, I mean, granted, it's not insignificant, but 50% defoliation, that's huge. That's a really large amount. It's
SPEAKER_03:huge, and it looks very scary. It looks terrible, right? But the rice is tough, and it can, you know, it loses some, but it's not going to lose all. When we defoliated the rice all the way to the water level, So we cut it all the way to the water, you know, as best as we could. There's always some living that stayed above the water. Then we would find a good 25% yield reduction when we do that.
SPEAKER_02:And that would be 100% defoliation estimate.
SPEAKER_03:That's what we would call 100%, yeah. And so we saw that, you know, in 2015, right, 2015, when we had the outbreak, some areas were just, you know, it into the water. And so those fields probably saw a yield reduction. But yeah, rice is pretty tough. And so it can take a lot of defoliation. The issue is, you know, okay, if these worms are eating and you're already losing about a quarter of your foliage, they can eat a lot very quickly. And so you don't want to get anywhere more than 25%. So that's why we make the threshold 25% defoliation. You don't want to get to 50% because then we know you're going to lose yield.
SPEAKER_02:Let's say we've got a field, we think we're approximately 25% defoliation. We've still got worms in the field that we're seeing. What kind of, I guess, control methods or management options are there for a grower, maybe starting cultural methods? Let's talk about those first. Does that primarily center around early season weed management? Or I guess that'd be before you see the worm. Yeah,
SPEAKER_03:I think early season weed management will have an effect, I think. We haven't done a formal study on this, but I mean, many times if you walk a field, you'll see the water grass, you know, it's all eaten up. They'll eat the water grass. And a lot of times it seems like after propanil sprays, those worms that were on the water grass kind of move to the rice or start eating the rice. That's kind of just an opinion. observation you know we haven't done like i said a formal study but it seems to be that way so i think yeah you know grassy fields might have offer more a variety of diet for the army worms so that might might play to play a role but if yeah if you get them you know and there's a high number of them and the defoliation is high, there's not much else we can do other than an insecticide.
SPEAKER_02:And I think we've got, you've already mentioned the chemical name of what we call Intrepid, that's the trait name. And then there's also another one, different chemical name that I can't think of right now, but Dimolin. But that one has a different pre-harvest interval, is that right?
SPEAKER_03:Yeah, Dimolin. So Dimolin is also a good armyworm product. It works well. It's a little slower than Intrepid, but it does keep control. Yeah, it's got an 80-day pre-harvest interval. So you have to be careful about how late you can put it on. So on a typical armyworm year and on a typical rice planting year, you can still use it for defoliation. But once we get into the second flight and the heading then if there was a need for an insecticide you couldn't use it then so yeah so we have in the intrepid demilin the pyrethroids uh that are common for other pests are really they do not work for our worms so i i would discourage people to to use them at all because we've done trials we've seen fields sprayed uh you know we've seen uh Pyrethro is combined with Propanil. Maybe control them when they're small, but they just don't work.
SPEAKER_02:Yeah, and so in that, you'd just be kind of throwing money away if you tried to treat armyworms with pyrethroids.
SPEAKER_03:Pretty much, yeah. It's not doing anything.
SPEAKER_02:Now, what if I'm an organic grower? Because these are obviously chemicals that you're using in conventional farming systems. But if you're an organic grower who's got a problem with armyworms, are there options out there for them?
SPEAKER_03:Well, you can use the BT products. They're not very effective. You know, over the years, we've seen up to 50% of efficacy. They just don't work as well because by the time we see the worms and we made the decision to treat, the worms are too big. The small worms, when BT would be more effective, a lot of times we just don't see them. It's really hard to see them in rice. They're hard to find. So it kind of misses that window. And at that time also, we don't know if, yeah, it's going to be enough population to cause defoliation. So it's challenging. The tools for organic growers are not the best. But the BTs are available and they will reduce the population somewhat, but it's not going to be as effective as the other, the chemical options.
SPEAKER_02:Is there anything, I guess, in terms of research on armyworms that you're working on this year or in recent years?
SPEAKER_03:Well, this year, mentioning earlier, we did an insecticide trial. And so there is a product that we're hoping it's going to be available soon. maybe next year, and it works as good as Intrepid. So it will give us a, and it's a different mode of action, so it'll give us a really good rotational alternative. We looked at another product also that's a biological, it's a fungus that would colonize the armyworm and kill them. But unfortunately, it did not really do much.
SPEAKER_02:Oh man, because that sounds exciting.
SPEAKER_03:Right, yeah. And these products work in other systems, but again, rice is just not very good. The way we use these products don't work as well.
SPEAKER_02:Yeah, it's just rice is interesting in a lot of ways. A lot of things that might work in other row crops don't tend to always transfer over.
SPEAKER_03:Right, yes.
SPEAKER_02:Well, Luis, thanks for talking with me today. Anything else you want to bring up while we're on?
SPEAKER_03:Yeah, and well, you know, I think, like I said earlier, we're seeing more worms than the past few years. I think, you know, growers should keep that in mind. We're already... past that first peak, but there's a second one. And we'll see if those populations track this first infestation. And if they do, just keep an eye on the field. The second one's a little trickier, because the injury occurs on the panicle. And once it happens, there's no reducing that. Once the injury is done, it's done. But we don't know exactly at what point it happens. Does it happen as the panicle's coming out? Can it happen once the panicle's out and it's already filled? What is the window of susceptibility? We haven't been able to determine that. So I think it's just a matter of... being aware that, okay, there might be some worms and just keep an eye on it.
SPEAKER_02:That's a great note, Luis. And actually I'll link the episode we did last year on the second peak of army worms in the show notes. So if people want to just get a nice one, two punch of first peak, second peak army worms, we'll have that ready for them.
SPEAKER_03:Okay, great.
SPEAKER_02:Well, Luis, thank you so much. And we will see you around. No
SPEAKER_03:problem. Thank you.
SPEAKER_02:We've got a couple of upcoming events that are rapidly approaching. The first event that's up on our schedule is the Rice Production Workshop, which is a workshop we hold every two years to cover the basic principles and practices of rice production in California. This event will take place July 23rd and July 24th, 2025. This is a two-day workshop. These will be two all days, so it will start at 8.30 a.m. and go till 3.30 p.m. and take place at the UC A&R building on 2801 2nd Street in Davis. Registration is required for this event and if you go to our UC Rice website there is a link for that registration. Our next upcoming event will be the Weedy Rice Workshop which will take place August 5th, 2025 from 10 a.m. to 1 15 p.m. at the Roberts Union Farm Center in Stockton, California. This will be a workshop devoted to the history and current management practices of weedy rice in California. Registration is not required for this event. Our final upcoming event for this season is the annual Rice Field Day, which takes place every year on the last Wednesday of August, which is August 27, 2025. It starts promptly in the morning, so be sure to get your coffee and donuts when the field day starts, and it will take place at the Rice Experiment Station at 95 And as always, stay tuned for some great talks and a delicious lunch. For more information about these and other upcoming events, feel free to check out our resources, which include the UC Rice blog and the UC Agronomy Rice website. In terms of other resources you may want to take advantage of, you can also look at our newsletters, which include Rice Briefs, which covers Clusiolo, Rice Notes, which covers Yuba Stutter, Rice Leaf, which covers Butte and Glen, and Field Notes, which covers rice in the Delta region of California. Thanks for listening to Thoughts on Rice, a University of California Cooperative Extension podcast from University of California Agriculture and Natural Resources. You can find out more about this podcast on our website, thoughtsonrice.buzzsprout.com. We'd love to hear from you, whether it's from using our text link in the show notes, a survey submission in our feedback form, also in the show notes, or in a comment or rating on your podcast streaming service. of choice. You can also email us with any comments, questions, or concerns at thoughtsonrice at ucdavis.edu. Thanks for sticking with us over this planting hiatus earlier this spring. Rice season is well underway, and we hope you stay safe this season. And remember, like the growers like to say, have a rice life. Mention of an agrochemical does not constitute 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.
