Contact David Crowder by email at firstname.lastname@example.org or by phone at 509-335-7965.
View Dave’s previous podcast episode.
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Drew Lyon: Hello, and welcome to the WSU Wheat Beat Podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. We have weekly discussions with researchers from WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production. If you enjoy the WSU Wheat Beat Podcast, do us a favor and subscribe on iTunes or your favorite podcasting app. And leave us a review while you’re there so others can find the show too.
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Drew Lyon: My guest today is Dave Crowder. Dave is an Associate Professor of Entomology at Washington State University. His lab, which currently has eight graduate students and four postdoctoral scholars, works on a variety of insect-related issues in agricultural crops. He has worked extensively in small grain systems, on wireworms, aphids, and integrated pest management. Hello, Dave.
David Crowder: Hi Drew! Great to be here.
Drew Lyon: Thanks for joining me today. Our topic today is aphids. What are the main aphids that attack small grains in Washington?
David Crowder: Great, thanks Drew. And again it’s great to be here. You know, we’ve been getting a lot of questions lately about aphids so we felt this podcast was really timely and there’s four or five main species of aphids that are attacking small grains in Washington State. They include a species called the cereal aphid, which is a relatively new aphid found in this region, but now which is the most common aphid that we’re finding and sampling. And a lot of sampling works going on here at WSU, as well the University of Idaho being primarily led by Dr. Sanford Eigenbrode’s lab. That cereal aphid has become one of the most common aphids here in Washington though. And some preliminary studies show that it can cause a lot of direct damage to wheat. Up to 30-40% yield reductions in some of the experimental trials that are going on at Idaho. Some of the other species that have been here and documented for a long time include the bird cherry-oat aphid, the English grain aphid, a species called greenbug, and then the Russian wheat aphid, which was historically more of a problem but really is not that abundant anymore. And so all of these aphids differ in their appearance, they are different sized, they have different colors, but there is some good information in the Pacific Northwest Handbooks to kind of help folks identify these different species of aphids. Some of the things to look for besides just identifying aphids in the field, they often will cause or prevent leaves from unrolling and so if you see kind of leaves curled up oftentimes that’s due to aphid feeding and they will be inside. And then certain species of aphids can cause striping on the leaves, so distinctive patterns on leaves that are characteristic of aphid feeding. And then one of the big issues again with aphids in addition to kind of their direct feeding is that some of the species can transmit barley yellow dwarf virus, which can be problematic for growers both spring and winter wheat growers can suffer from barley yellow dwarf virus.
Drew Lyon: I know that’s been a problem sporadically over the last few years.
David Crowder: Yes. Yeah. It has, you know, the neonicotinoid seed treatments, which are you know, commonly applied in this region, both the spring and winter wheat have been shown to provide protection against the vectors of barley yellow dwarf virus for about 150 days after emergence of the crop. And so I think that we’re seeing, you know most growers are using a seed coating with a neonicotinoid, barley yellow dwarf virus has not been as problematic as it may have been previously.
Drew Lyon: OK. You mentioned some PNW Guidebooks that have some good information. Is there a website people can go to, to find those?
David Crowder: Yeah, there’s… if you look up the Pacific Northwest Pest Management Handbooks those are all online and are searchable by crop, by the insect pest you want to look for. So the PNW Pest Management Handbook and then you would just go to Agronomic Crops and Wheat. And it has a lot of information. We also have information that links to that handbook and other publications on the small grains website at smallgrains.wsu.edu. And a lot of the information is cross-linked at that site as well that people can go and find out about.
Drew Lyon: OK, excellent. We’ll make sure we put that information in our show notes. So these different aphids out there working, how does a grower go about scouting and finding out whether he’s got a problem with one of these insects? And do you scout for them at the same time or are they different times?
David Crowder: No, you do — a lot of these aphids are occurring at the time throughout the season. So the scouting you can pick up a lot of these aphids at similar times of the year. What we, you know, visual scouting is usually the best way to sample for aphids and what is typically recommended, especially if you’re seeing some of those characteristic symptoms like leaf rolling or the streaking on the leaves, but even if you just want to see if aphids are there. We typically recommend to growers that you want to sample a good number of plants in your field through visual observation. Aphids tend to be fairly patchy within fields because they reproduce asexually. That means a female will just produce her own offspring and she doesn’t need to mate. And those offspring will be a clone of that initial female. And so what tends to happen in a lot of cases is aphids will move in, a single female will fly into a field, she’ll start reproducing and her babies will kind of stay on the same plant. And that tends to create a pretty patchy distribution. So if you’re just sampling a couple plants, you may miss them. So what we often recommend is, you know, starting in May or June that you may want to walk what we call a transect. You know, start at the field of edge, maybe identify a plant, try to look at every tiller and, you know, count the number of aphids that you might see. Then maybe move, you know, five meters into your field and you know, scout another couple of plants and kind of work your way into the center of the field trying to scout maybe 20 or 25 different plants and counting the number of aphids on each plant visually. You know, typically that can be done just, you know, at 30 seconds or a minute looking at a plant you can get a good sense of whether or not there’s aphids there and what their density might be.
Drew Lyon: And for people who might not be familiar with the metric system five meters is about fifteen feet.
David Crowder: [ laughter ] Fifteen feet or so yeah, yeah, yeah. So you know it doesn’t have to be completely precise but the point is you know, you want to kind of sample not just along the edge but into the interior of your field and you want to make sure you’re not just sampling in one location because you might miss an infestation that’s occurring.
Drew Lyon: Twenty – twenty-five plants?
David Crowder: I think twenty-five plants is a good kind of baseline to get a number of, you know, what’s going on in the field. And if those aphids are present you should be able to pick them up with that kind of sampling.
Drew Lyon: OK, very good. What are the — if people find these aphids is there a threshold for them and then if there is and they exceed the threshold what are some of the control strategies used on aphids?
David Crowder: Yeah, it’s a good question. I think on of the reasons we get a lot of questions from growers about aphids is, unfortunately, there aren’t really good thresholds for many of these aphids. And so you know, if you read different literature it might suggest anywhere from two to ten aphids per tiller or per stem or per plant is the threshold, but unfortunately, at least in this region, we don’t really have solid data on what those thresholds are and so I think it’s sometimes, you know, growers are spraying when they don’t need to be because we haven’t established those economic thresholds. But depending on the species and the stage of the wheat, it’s probably somewhere between 10 to 20 aphids per tiller is the threshold. Those thresholds tend to get higher and higher as the wheat matures. So younger wheat, younger barley, is much more susceptible. It’s more susceptible to the viruses as well as the direct feeding damage, you know, aphids can also produce this sugary substance called honeydew, which is a waste product that can be a substrate for molds and all of these things are more damaging, you know, right after emergence in the early stages. So aphids can be problematic up until about the flowering stage. You know once wheat gets into the milk stage, it’s been shown that treatments are not effective at all. So some of the things that are effective for aphids, as I mentioned before, the seed applications of the neonicotinoids, those have systemic activity, which means you know they move throughout the plant and they continue to be effective for a long period of time. So things like Gaucho, which is imidacloprid, Cruiser, which is thiamethoxam, or clothianidin, which is Nipsit Inside. Those have shown to be effective and provide control long after emergence for several months. However, if growers are seeing an infestation there are a lot of options of different insecticides they can spray, primarily the pyrethroid insecticides, organophosphates, dimethoate, which is something a lot of growers use, can be effective if applied early enough in the year. Another factor with aphids though is that primarily they are often controlled by their natural enemies. So in this region, there are a lot of parasitoid wasps that will lay eggs on aphids and kill them. Lady beetles are really voracious consumers of aphids, things like lacewings, some of these predatory insect species that growers might recognize are really, really effective at limiting aphids. And just in the middle of the summer heat is just a really, really main control strategy against aphids. You know, once it gets into the hottest part of the year, you know, aphids are really, really just knocked back by heat. And so, you know, these are periods of time when growers don’t need to be spraying. So you know relying on these biological control agents typically is going to do the job for you that, you know, aphids are kind of sporadic pests in this region. You know, unless they’re really, really abundant early in the year when the wheat is small, the biological control agents in the weather are probably going to do the job. There is some evidence as well that plants that are water stressed or nutrient stressed are more conducive to aphids as well. So just maintaining proper fertilization can be an effective kind of cultural management strategy. You know, most of our growers obviously around here are not irrigating, but you know, trying to maintain healthy plants is usually just a good defense against aphids. And then trying to manage volunteer plants, things of that nature, you know, a lot of these aphids that we’re talking about are generalist species. So they’re not only feeding on crops but they’re feeding on a wide range of grasses. So you know, trying to practice proper sanitation, you know, burning stubble. You know, some of things people do around here are probably effective at controlling aphids in the long term.
Drew Lyon: OK. I know this past season as grain got into the grain filling stage, or as wheat got into the grain filling stage, we had a number of calls about, you know, “I have aphids should I be spraying?”
David Crowder: Right.
Drew Lyon: And I went into the literature and there’s a little bit of information out there. All of it I found said, you know, it’s not worth it but evidentially there’s a lot of people concerned about it at that point and I think there are growers treating at that stage so what recommendation do you have for growers if they see aphids in their wheat heads?
David Crowder: Right, so you know one of the aphids that becomes — you know is fairly active in the middle of the season is this English grain aphid and it’s the largest aphid that we have here on the Palouse. And it likes to hang out on the heads and so, you know, I think what growers often see that there are aphids around and they appear to be feeding on the heads. And so, you know, I can understand why it looks like these guys might be doing a lot of damage but all the — and you’re also right that there unfortunately, is not a lot of published literature on how damaging these pests are. There have been some studies at Idaho in particular that have shown that treating the grain basically after the milk stage gives you no economic benefit at all. It’s knocking out the natural enemies and as I said, it’s really — the aphids are not going to damage your wheat once it gets into the milk stage. So what we see in Washington unfortunately, is a lot of growers are using dimethoate after grain fill. And we think it’s because they’re seeing these aphids on the heads of their plants. They look like they might be damaging, you know, they are these big large bodied aphids. But our recommendation to growers after that milk stage is basically to do nothing. You know just to try to maintain healthy plants, those natural enemies do a really good job of controlling the aphids and when it gets hot into the summer, spring insecticides are going to do more harm than good. And so, you know, even though some of these insects look like they are going to be out there, but they’re really not going to be damaging the wheat. So at that stage, we recommend to the growers really to not do anything and let nature take its course. The natural enemies and the weather should control the aphid populations in the mid-summer.
Drew Lyon: And natural enemies tend to be slightly in lag of the pest population. So it may look like while like the aphids or whatever pest is are starting to take over but if you give it a little time —
David Crowder: That’s right, and some of these — as I mentioned these parasitoid wasps, which are kind of specialists on aphids, and a single wasp can lay, you know, can kill 100, 500 aphids in a day. So some of these natural enemies are really, really synced up as you mentioned that once aphid populations start to grow there’s a little bit of lag but then they can come in and wipe out those populations very quickly. They’re adapted to do that. And if you’re spraying insecticides at those points you’re probably just killing off a lot of those natural enemies. They’re very, very susceptible to those things and so you’re not getting that benefit of that natural control and it’s just going to be an economic waste. And we, unfortunately, are seeing probably tens of thousands of acres that are spraying their wheat with organophosphates or pyrethroids in the middle of the summer when we really think that’s not an effective strategy. It would be nice if overtime we would like to get more science-based evidence that, you know, this really is an ineffective strategy but, you know, from everyone I’ve talked to, you know, all the researchers as well as, you know, different scouts and stuff, you know I think anecdotal it’s been shown time and time again that spraying your wheat, you know, once it gets really established after it’s flowered it’s not going to be an effective and economical strategy for aphids.
Drew Lyon: All right, Dave thanks for sharing that information to our growers. I think it is a timely topic and I appreciate your time.
David Crowder: Great. Thanks, Drew. Thanks for having me.
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Drew Lyon: Thanks for joining us and listening to the WSU Wheat Beat Podcast. If you like what you hear, you can subscribe on iTunes or your favorite podcasting app so you never miss an episode. And leave us a review while you’re there. If you have questions for us that you’d like to hear addressed on future episodes, please email me at email@example.com. You can find us online at smallgrains.wsu.edu. You can also reach out on Facebook and Twitter @WSUSmallGrains. The WSU Wheat Beat Podcast is a production of CAHNRS communications in the College of Agricultural, Human, and Natural Resource Sciences at Washington State University. I’m Drew Lyon. We’ll see you next week.