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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
Second peak of armyworms with Luis Espino
Feedback Poll
Together, the UCCE Farm Advisors seek to provide relevant, topical research-backed information relating to CA rice production.
Today Luis Espino and Sarah Marsh will be talking about Rice Armyworm Monitoring Program and the second generation of armyworms in rice.
Two true armyworm generations occur in rice; moths fly in spring and early summer, laying eggs in rice fields and surrounding vegetation. The larvae that emerge feed on rice foliage. A second moth flight occurs in mid-summer, followed by larvae feeding on rice foliage and panicles.
Upcoming Events!
- UCCE Hedgerow Demonstration Day on August 14
- Annual Rice Field Day on August 28
- Rice Pest Management Course on September 4 *registration required*
Armyworm Resources
CA Armyworm Trapping Network in Rice
UC IPM - True Armyworm in Rice
Other Resources
Rice in the Delta
Feedback Poll
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 Marsh, and I'm a rice farm advisor for Yolo and Colusa counties. I'm Whitney from the forest. I'm the Cooperative Extension Rice Advisor for Sutter, Yuba,
SPEAKER_02:Placer, and Sacramento counties. My name is Luis Espino. I'm the Rice Farming Systems Advisor for and Glynn counties.
SPEAKER_00: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:Together, the UCC rice farm advisors seek to provide relevant, topical, research-backed information relating to California rice production. Today, Luisa Spino and I will be talking about the Rice Armyworm Monitoring Program and the second generation of armyworms in rice. Two true armyworm generations occur in rice, with moths flying in spring and early summer, laying eggs in rice fields and surrounding vegetation. The larvae that emerge feed on rice foliage, with a second moth blight occurring mid-summer, followed by larvae feeding on rice foliage and panicles. This year, the first armyworm generation hit its peak at the end of June, with an average capture rate of 43 moths per trap per day at peak. We calculate these numbers based off 15 trapping locations, spanning from near Pleasant Grove up to north of Willows. Luis coordinates the trapping network with Corteva AgroScience and AgPest Monitor. We're expecting the second peak of armyworms in mid-August, based off both historical data and in-season moth populations. Luis, we're going to talk about armyworms and rice. Can you give us some background on this worm?
SPEAKER_02:So armyworms have always been an insect that's present in rice. I don't think there was ever much concern about them. I've been working in rice in California since 2007. A couple of times before 2015, I got calls about armyworms. And I can remember one was a seed producer. And so he was concerned about, he was seeing some injury on the panicles. and he was concerned about it. He was going to get too much injury. And so that was one time. And then a second time was actually in one of our variety trials. We were just seeing a lot of defoliation. But this is before the armyworms got on the spotlight. And that happened in 2015. So in 2015, we had a huge armyworm outbreak. So it came out of nowhere. It caught everybody by surprise. The first action was to use pyrethro because that's what we had been using for armyworms until then. But that's when we realized that the pyrethroids really do not control the armyworms really well. So since then, we've done a lot of trials. And if we get maybe 60% control, that's high for pyrethroids. So anyway, that was 2015. We had no products, and growers were using malifactants. thion and using pyrethroids uh dimeline was an option but i don't think it was used much and i'm not really sure why but then you know the the rice commission got you know got to work right away when the the outbreak happened and they were able to get a section 18 for intrepid and the section 18 came a little late after that first the first defoliation had happened but was available for the second, now we know, the second flight of the armyworms. But we didn't see the second flight and the second infestation wasn't as bad as the first one. So that's a little bit of the history. And so since then, we've seen the armyworms. Some years, you know, they get bad. In some years, we see very few of them. So it varies quite a bit. And if you read a little bit about armyworms and their biology on on the literature, you see that they're known for that. Every so many years, something triggers these huge populations and they just, you know, they can do a lot of damage. And this has been recorded since the late 1800s. But what exactly causes these outbreaks? Nobody knows.
SPEAKER_01:That's really interesting. You mentioned something about first peak versus second peak. Can you explain a little bit about what the first peak is and when it happens?
SPEAKER_02:Yeah. And so So we've had traps for several years now. And what we see is these traps are for the moths. And we catch the male moths on the traps. And so we see a flight that starts maybe at the end of May and then increases rapidly with the number of moths in the traps increases and peaks, depending on the year, anywhere between late June to early July. And then the numbers start going down very rapidly. That's the first flight. Then the numbers go down to zero at about this time. We are in July 26th. So at the end of July, there's no moths in the traps, but then they'll start coming up again in early August. And then they peak by mid-August. And then they start coming down again after that. And then they kind of go away. But so those moth peaks are followed by warm infestations in the field, right? And so if you think about it, the moths, They fly, they mate, they lay their eggs around rice fields. And then the worms have, you know, there's going to be a lag between the egg laying and the worms when we can see them and they start doing damage on the rice. And so that lag is about a week. And so when the moths peak on the traps, we know that about a week later is when we're going to see the most worms in the field.
SPEAKER_01:So the different timings of the peaks, they're at different points in the season. So the rice is at different stages. What type of damage do we see at each of these different peaks? And how does the injury threshold change depending on how many moths fly at the first peak versus how many moths fly at the second?
SPEAKER_02:And the first infestation or the first generation of worms is the defoliation is what's the problem. So they'll defoliate the rice. In 2015, we saw defoliation that was all the way to the water level. That's why they were so problematic. And so at that point, the The threshold that we talk about is 25% defoliation. So you don't want to let the worms eat more than 25% of the rice canopy that you have in the field at that time. We've done trials where we've, you know, defoliated rice artificially to see when we start seeing a yield effect. And rice can take a lot of defoliation. We defoliated rice all the way to the water level. And when that happens, we see a yield reduction of about 25%. The rice grows back, but it doesn't yield the same and it might be slightly delayed. On our trials, we've also defoliated rice 50% and we see a yield effect with 50%. With 25%, we don't see a yield effect. But it doesn't take long to go from 25 to 50. I mean, those worms, they feed fast. And that was kind of why everybody was caught, you know, by surprise in 2015 is because it kind of coincided with 4th of July weekend. And a lot of people went on vacation, you know, three, four days. They came back to no rice. The injury can happen fast. So we consider 25% a good threshold so that we don't let it get anywhere close to 50% when our research shows that you can get a yield effect. Then later you get the second peak or the second generation. And that happens when there's panicles. And then at that point, there's so much foliage. I've never seen a rice field defoliated totally by armyworms at that point because there's just so much foliage. Armyworms will defoliate. They will feed on rice leaves, but that doesn't seem to do anything to the rice in terms of yield. But they will feed on the panicles and that's where the problem is. And so they can feed on the panicles. They cause this blanking of branches because for some reason they like to bite on, on the branches of the panicle. We have not any recent research at this stage of injury, but there's information from the early 80s where they did the work. And they considered that if you saw 10% of panicles injured by armyworm, then probably a treatment was needed.
SPEAKER_01:So at that late stage in the season, there must be kind of limited options for treatment. What can you do at second peak if you see a significant amount of damage.
SPEAKER_02:If there was need for treatment at that point, we can still use Intrepid. Intrepid will be effective at that stage. Right now, that's the only option we have. The other product we can use for armyworms is Dimlin. However, Dimlin can be used early, so during the first generation, but it cannot be used on the second because it's too late. Dimlin has a pre-harvest interval of 80 days, and so there wouldn't be enough time from treatment to harvest if the treatment's done at the heading stage. So right now we only have Intrepid, which is very effective and works very well, but there is some work right now trying to get another option registered.
SPEAKER_01:Are there any other non-chemical strategies available that are effective when controlling armyworms?
SPEAKER_02:General agronomic, you know, good cultural practices will have, you know, some effect on the plant in terms of just having a robust plant, you know, having a good stand, having good weed control, we do see sometimes we find that the armyworms like to feed on the water grass. And so these weeds can be kind of a host for the armyworm. We don't really know the role the weeds play, but if you have a clean field, maybe it's better than a field that has a lot of weeds.
SPEAKER_01:I remember years ago when you and I were scouting for armyworms, we started on the ditches and on the levees first, where the weeds were overgrown and at a larger growth stage than the rice, and that's where we found the armyworms first, feeding on the outsides, the borders of the fields. Would you say that that kind of standard holds through? You see them on the borders first before they move towards the middle of the field, or is it kind of random?
SPEAKER_02:You know, the first generation, the first peak, you know, the first peak of armyworms in the field, yes, they start on the borders. They might start near levees, and then they move into the field. The second generation, we see that more uniformly distributed across the field. What happens is, so these moths are laying the eggs, not in the rice fields, but around the rice fields, maybe on the levees, maybe on ditches, on the banks. And then from there, the worms make it into the rice. But once they're in the rice, if you've ever looked for worms, about this time of year, you'll find the pupa. And they do pupate in the rice fields. So they'll pupate. They lodge themselves between the tillers and make like a sort of a nest there with their frass and dead leaves and make a little nest and pupate there. And it seems like those moths, when they emerge, they just lay eggs in the rice, some of them at least. And so that's why we see a more uniform into the field type distribution. Something interesting about the armyworms is that we don't know where they're laying their eggs. I haven't been able to find the eggs, you know, and we've looked for them. They are very good at hiding the eggs. Reading the literature, they tend to prefer dry stubble. That's where they would lay eggs. But it doesn't seem like they are laying them in the rice because I've never been able to find the eggs. And an anecdote that I like to tell is there's this famous entomologist from the late 1800s, Ed Riley. And so he did some work on armyworms. And at the time, he offered... a$20,000 reward for anybody that could find the armyworm eggs. And apparently nobody was able to claim the reward because they couldn't find it. So they're very cryptic. I know for the research purposes, they have armyworms in cages and there they lay eggs on the rice and you can see, that's how we know what the eggs look like. But in the field, it's really, I've never seen them. So I don't know where they're being laid.
SPEAKER_01:And with that kind of incentive, you'd think somebody would have found at least one egg mass. I
SPEAKER_02:would think so, but
SPEAKER_01:apparently not. Yeah,
SPEAKER_02:so we've been doing these traps, you know, we started with just six locations. And I think we started maybe in 20, just right after the big outbreak. So 2016. But then in 2018, I think Corteva came and asked if I was interested in expanding the program and, and to their credit, you know, they wanted to see it happen. I was a little, a little hesitant that I was going to have the time to have more than six locations. Fred Rehrman from Corteva, he asked if we could do more locations and they provided support. And so we expanded to 15 and we've had the 15 locations since then, 2018. And like you say, we send these alerts, you know, during the season, every week. Some growers, some PCAs might not, might be tired of seeing them, but I think they're a good reminder of, you know, this is the time to look for armyworms or right now there's no worms in the field. So you don't have, you know, you don't have to worry about it. worry about it. But yeah, we've been doing this for quite a few years now.
SPEAKER_01:Can you explain a little bit about how these traps work to capture the moth populations?
SPEAKER_02:Yeah. So the traps are just buckets and inside the bucket, there's a lure and the lure contains a chemical that's called a pheromone. And the pheromone is a chemical that female moths produce and specific for this species of armyworm. And so it attracts the male. So the male things that there's female moths in the bucket. And so they go and they try to get in the bucket and then they get caught. So inside the bucket, we also put a kill strip that when they get in the bucket, it kills them. And so it's this pheromone that attracts the moths. And like I said, they're very specific, species specific. So we don't find any other species in the buckets other than army one.
SPEAKER_01:So after analyzing the results from these traps, how have has this year turned out in terms of worm populations? Higher than normal, lower than normal, or pretty much equivalent to what you were expecting?
SPEAKER_02:So I would say this year in terms of the moths, it's been pretty average. I think what the numbers we've got on average for the Sacramento Valley is about at the peak, the first peak, 50 moths per trap per day. Other years are anywhere between 30 and 40. So maybe a little above average. And we have seen in some locations higher numbers of worms than previous years. So we do have a few fields that we go to every year and we look for worms, you know, as we're doing this trapping, just to get a sense of what's the worm population. And yeah, certainly this year we've seen more worms. Right now there's no worms in the field. They've all cycled out. But having said that, you know, the moth numbers don't really relate to the worm populations in terms of numbers. So for example, last year was the year we got the most moths on the traps than any other years we've been trapping. But we did not see worms in the field. Very, very few worms. So every year is different. What the traps tell us is more about the timing on when the worms are going to be in the field, not so much the numbers. So unfortunately, we cannot just rely on the number of moths in the traps and say, yes, we do need to spray or now we don't need to spray. where you still got to get in the field and look for the worms.
SPEAKER_01:Do you have any kind of expectation for the number of worms coming up in this second peak?
SPEAKER_02:So the second peak is typically lower than the first. In general, this second infestation, we don't see as much damage as the first, but because it's during heading, I think, you know, growers and PCAs are a little bit more sensitive to the damage and, you know, seeing some damage, it's more worrisome for them at that point. But so, yeah, in general, the second is usually lower than the first. But, you know, we'll see.
SPEAKER_01:All right. We will. We will see, Luis. Thank you for taking the time to talk about this today. Is there anything else you want to share with us today?
SPEAKER_02:Yeah. So this, like we were saying earlier, you know, we've been doing this worm trapping for quite a few years. And so we've been analyzing the numbers that we get. And over the years, the numbers vary, but the time means don't vary too much across the valley and so when the moths peak say are more north the trap we have the furthest north is on road near road 47 in glen county and the furthest south trap we have is near the sacramento airport and they peak about the same the same time so there's not a lot of variation on the timing of when the moths peak and then therefore where when the the worms also
SPEAKER_01:That's really interesting because for people who aren't specifically familiar with those areas, there's quite a bit of mileage between those two different
SPEAKER_02:locations. worms they're they're migrants and so they're moving in probably from southern california into our area and that's why they kind of show up all at about the same time the true army worm is known to be a migrant in northern latitudes like in canada and so they've they've done some work and they know that their moths they come up from the northern part of the u.s and actually probably some of our moths might make it up up there their winters are so harsh that there's no chance for having survival there during the wintertime. There's no overwintering. So there must have to be migrants coming from somewhere else. But I think we are probably in a similar situation.
SPEAKER_01:Well, Luis, keep us posted and we'll be sure to keep an eye out for those worms as the summer progresses. Thank you for your time. We have a few upcoming events that we'd like to share with you all. The UCCE Hedgerow Demonstration Day will take place on August 14th. It will start promptly at 10 and go until 12, and will take place at a grower-collaborator field between Grimes and Arbuckle. We will meet at the corner of Lodi and Tooley Roads. There is information on that in the show notes. The annual rice field day is coming up on August 28th. That agenda starts at 8 a.m. and goes until noon and will take place at the Rice Experiment Station in Biggs, California. The field day will consist of field tours, talks from breeders, and a delicious lunch. Our final upcoming event will be the Rice Pest Management Course, which will take place on September 4th and be hosted at the Rice Experiment Station in Biggs, California. This event will start at 8 and go until 3 and will consist of pest ID workshops, field tours, a light lunch, and an afternoon session devoted to pest management in rice. Registration is required for this event and the link to that registration will be in all of our resources as well as linked in the show notes. Thanks for listening. And like 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 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.
