Scaffolds 2024 Digest: Week 10
This post is a text digest of the Scaffolds Podcast. To listen to the original episode, visit the following link: Scaffolds Podcast on Spotify
On this week’s episode of Scaffolds, I talk to Dr. Tracy Leskey, an entomologist at USDA-ARS and the director of USDA’s Appalachian Fruit Research Station. And we are also joined by Dr. Laura Nixon, a postdoctoral researcher in her lab working on apple pest management. Kerik lets us know about the potential for powdery mildew, and Anna gives us our weekly state of the state update on trap captures and degree day accumulations. So today I’m here with Dr. Tracy Leskey, an entomologist at USDA ARS and the director of USDA’s Appalachian Fruit research Station. We’re also joined by Dr. Laura Nixon, a postdoctoral researcher in her laboratory.
Monique Interviews Dr. Tracy Leskey and Dr. Laura Nixson
Monique: So, hi, Tracy and Laura. Welcome to Scaffolds.
Tracy: Hey, thanks, Monique. Good to see you. Thanks for having us.
Monique: So, I wanted to have this conversation with you both to discuss all of the apple pests, and you, Tracy, have worked on most of them, and right now in particular, we are in plum curculio season. So I wanted to ask you, what are your thoughts on plum curculio? I think it’s one of the more difficult pests to control in the system. And do you think there’s been any real big research developments on how to control this?
Tracy: So, you know, it’s interesting because plum curculio was sort of in the background for a while, while we were chasing invasives like brown marmorated stink bug. And with the broad-spectrum materials we are applying against that pest, plum curculio was kind of still there, but not as evident as it had been, especially in the mid-Atlantic. As we’ve seen sprays being dialed back against brown marmorated, we’re seeing plum curculio become more of a problem. And you’re absolutely right, Monique. It’s a challenge pest. It, you know, it’s active mainly at night. It generally disperses out of wood lots. If it’s cool and wet, it extends their oviposition period, egg laying period, even longer. And timing sprays because of that lag and trying to hit everybody, usually by petal fall, we see, you know, maybe 40, 50% of the weevils already in the plots, but that means they’re still, you know, 50% to 60% that could still arrive a little bit later. And that’s where it really becomes challenging.
Monique: So we generally manage this with sprays, but I guess because they’re an edge pest, do you think that it’s worthwhile to do edge treatments, or should the whole block be treated?
Tracy: We generally, when we’re doing our research, associated, and I’ll talk about some of the border-based strategies we’ve worked with, because I agree, it’s, you know, you can use border sprays, but at petal fall, they can already have made it into the center of the block. So usually, it’s a petal fall treatment followed by potential border sprays. That’s something that the Canadians, as well as Anne Nielsen’s lab at Rutgers has worked on. Or what we’ve used as well is this attract and kill, affectionately known as the bomb tree, where you attract, aggregate the adults in a single canopy and then only treat that canopy. So you’re just reducing your inputs further. And that’s worked fairly well in places where we’ve done most of the research to date, which was in New England. So we work with growers in Massachusetts, Vermont, and New Hampshire, and that’s been pretty effective over the years.
Monique: So is that tree a different species, or do you kind of pick a certain tree to focus on?
Tracy: So what we do is we use an apple tree, but we make it more stone fruit, like by adding benzaldehyde, which is a volatile that is very commonly released by stone fruit, along with the male produced aggregation pheromone of plum curculio, grandisoic acid. And so those combined stimuli produce a synergistic effect in terms of attraction of the weevil. And so you can get them into the canopy itself. There’s not a whole lot of spillover beyond that canopy, and you can, you know, really just deal with them there. The other thing that we often have done over the years in, in tandem with this is to use the degree day model that Harvey Reissig developed to sort of put an end on that egg laying period as well.
Monique: So our growers here actually use that model via NEWA. It’s just such a difficult pest to control because once it gets going, unless it’s covered by another spray, you can end up at the end of the season with a really high percentage of damage on the fruit.
Tracy: Exactly. And also because when you have a rainy season like we are having now, again, it’s going to extend and coolness, it extends their egg laying period. And of course, the residues are less effective because of the rainfall, and so it’s sort of a double whammy. And we’ve seen that over the years, you know. And also a lot of the insecticides that we can use aren’t what we used a couple of decades ago, and so I think it makes it more tricky to manage them effectively and the timing even becomes more important. So you know, we’ve been looking at alternate strategies where we want to extend that residue a little bit longer by perhaps using a low rate of Surround in combination with an insecticide. Because the Surround itself, which is kaolin clay, it’s an irritant. It blocks up their spiracles, funks up their mouths, you know, their mouth parts. And so we’re in the second year of doing trials here on the farm. We haven’t done anything with growers yet, of course. We’re still experimenting, but it looks like it might provide another mechanism for protecting the fruit by deterring them from being on the fruit and foliage and walking throughout the canopy.
Monique: Yeah, I was thinking that it’s interesting that we don’t use Surround that much on the east coast. Surround is used a lot on the west coast, part because it’s used as sunscreen, because it’s so right there. So they’re active at night. But do we have any idea what they’re doing when they’re overwintering?
Tracy: So, generally, the best, the best data that exists on overwintering behavior was collected by our colleagues in Quebec, and they did a radio labeling experiment, which you couldn’t do now, but they were able to radio label the insects and look at how far they moved outside orchard blocks. And what they found was once they hit an area with leaf litter and duff and things like that, they would stop, they would just crawl under there, apparently overwinter successfully. We’ve done experiments, and I did some when I was doing my PhD at UMass, where we overwintered individuals outside under different, you know, sort of giving them different natural coverage to see how well they overwintered, so that they seem to do just fine, though, you know? So that’s where they are. They’re just waiting. And then once we hit, usually by pink, at least here in the mid-Atlantic. And also, we used to see it at UMass as well, to some degree. You start to see them trickling out at pink, I’d say on apple.
Monique: So, yeah, so they’re actually native to the US, right?
Tracy: They are, they’re a native. One of our native pests. They probably, you know, their favorite host is Prunus americana, our wild plum species. They also feed on beach plum. And then there are a couple of other wild hosts that they’ll feed on, some of our native Crataegus-type plants (hawthorns). They’ve even laid eggs in the southern range in muscadine grapes, they found them, but usually by far their favorite host, and the one that seems to allow them to really just get going is when you have something like wild plum or unfortunately when you have some abandoned apple trees, they can do quite well in apple as well.
Monique: So we’ve had this really mild winter this year. Do you think that plays a role like with the other pests and these guys being even more of a problem potentially this year?
Tracy: Yeah, I think we’ve been discussing in the lab and I’ll let Laura comment on this as well. We’re seeing a whole lot of everything this year. It seems like the mild winter has provided them with the opportunity just to be a lot of everything. I don’t know, Laura, do you want to talk about what we’ve been seeing?
Laura: Yeah. So both here on the research farm and I also work with a lot of commercial growers, we’re seeing a lot of lep pests. We saw the lep pests early and in much higher numbers. We’re seeing a lot of curculio damage already. We’re a few weeks past petal fall here now, three or four weeks past now, and we’re already seeing significant damage from plum curculio both here and in commercial farms. And yeah, it’s the spring for a lot of insect pests out and about, potentially because of the warmer winter or this, we get these very warm springs very early warm springs that then will freeze up again and then warm up again.
Tracy: Yeah, we actually are seeing a lot of brown marmorated as well. Early more so than we have for the past few years. So it seems to have been very favorable for overwintering insects this past season, unfortunately.
Monique: Yeah, I would absolutely agree with that statement. We saw live woolly colonies the last week of March. That’s crazy for up here.
Tracy: Yeah.
Monique: So let’s talk about the leps because that’s another thing on growers minds right now. And our trap capture numbers have absolutely been double, triple, quadruple what they were last year at this time. So I think that the leps are something that we assume we just know how to deal with them, right? But I think it’s a lot more complicated than that and I think with these warmer winters, it might throw off their development. So do you have any thoughts on leps and sort of like historically I think they are thought to be the worst pest. True, no?
Tracy: Yeah, and I’ll let Laura comment as well. They’ve always been in the mid Atlantic, the drivers of the system. You know, we would talk about codling moth and OFM and as the primary drivers and sometimes tufted apple bud moth and some other things. But yeah, that was always like the, you know, enemy number one, where those two leps.
Laura: Yeah and we’ve had a lot of reports over the last sort of four or five years of a lot of growers saying we suddenly have more lep problems. It’s been especially codling moth the last three years, but this year has really been the year of OFM as well. We have had crazy OFM trap captures as well. We got OFM, I want to say, maybe three weeks earlier than usual this year. And that first flight generation of OFM was like, like you were saying, like double or triple what we’ve seen in previous years, and both here on the research farm and out in the, in the growers orchards. The growers are really concerned about codling moths this year for sure.
Monique: So how, what’s the adoption look like in the mid-Atlantic for mating disruption?
Laura: It’s beginning to increase, because it’s been low adoption in the past simply because of mating disruption recommendations. You know, obviously here we have these small acreage, sort of non-uniform blocks within commercial orchards, and the recommendations on the mating disruption is that you need to have five acres or more in nice uniform blocks on a flat topography, which is just not the landscape we have here. But we have been doing some research on it along with collaborators on trying to find a way to make mating disruption more adoptable for this region. And we have actually had a lot of growers tell us that in the last year or two, they are actually putting mating disruption into their orchard. Some folks are putting it out, just mating disruption and relying on that alone. Others are putting out mating disruption and still doing their insecticide sprays over the top of the mating disruption. What we’re working on both in the research farm, but also we have a grower willing to work on this also, is having mating disruption up and having monitoring traps available to then spray the orchard when they hit a certain threshold. So, kind of combining that threshold trigger spray program with mating disruption to try and get a hold on these lep pests.
Monique: So then we can talk about the thresholds because that’s kind of a black box. So what are those thresholds? What are you guys using? And I guess we can talk a little bit about the history of those thresholds.
Tracy: I’ll talk a little bit about the history and I’ll let Laura talk about what our growers are doing. You know, I went down a rabbit hole a couple of years ago trying to understand recommendations for mating disruption for thresholds and just how we manage our lep pests because of these issues that Laura was describing, where growers are, you know, indicating they’re having more and more issues. And what I found was that there was no, I could not find a study that someone tested and validated these thresholds. And so I actually had the opportunity to ask your colleague Art Agnello one day when we were in a meeting online, and he said, yeah, it’s best guesses. And so as science is we do start with the best guess oftentimes, but what I wonder is if those thresholds were more appropriate for situations where we had really heavy hammers to kill these pests and how they work under the current chemistries that we have available. That’s the kind of thing that I think about a lot, and that we may have to make adjustments based on the thresholds of two decades ago may not be the thresholds that we should be using now.
Laura: And the thresholds that are generally recommended in this region are for codling moths. They’re generally recommended if you get 10 moths per trap per week, you should be spraying. And for OFM, it’s 30 moths per trap during the first flight or after that, 10 OFM per trap after the first flight. So we’ve been using 5 codling moth or 10 OFM in a trap as our thresholds. Yeah, but we’re also looking at using a lower number. So we’re doing these experimental thresholds with 2 codling moth per trap or 5 OFM. Now, this is layered over the mating disruption studies that we’re doing, but we’re actually finding that that lower number tends to trigger sprays at around about the same time as the higher recommended thresholds. Our working hypothesis is that either the moths are there or they’re not. If they’re there, they’re probably in flight. So, you’re probably going to want to treat them.
Tracy: In numbers that are damaging, it seems.
Monique: And when you guys are using mating disruption, are you using aerosol dispensers or passive dispensers?
Laura: We’re using the passive, the ties that you deploy in the trees. So you generally use, put double the amount around the border. So it’s usually one type per tree on the border and then every two or three trees within internally. We do have growers that are using the aerosols because they’re easier to put up and they can just sort of put them out and leave them. But we also have people using the ties that say it really wasn’t as much effort as they thought they were going to be to put all the ties in the trees.
Monique: So one thing I’ve heard anecdotally is that the aerosol dispensers kind of fall apart with topography. Is that what you guys have seen?
Tracy: I don’t think we’ve had enough experience with them yet Monique. Like Laura said, we’ve been just doing the hand applied dispensers, but at least one of our growers is putting out aerosol, so maybe we’ll see. I don’t know, have you guys seen something like that in New York with the work you guys are doing?
Monique: We haven’t, because in western New York, we don’t have a lot of topography. But in eastern New York, when I was presenting our results, I got that comment. So usually if it’s a comment and someone’s making it strongly in an audience, than it’s usually pretty true.
Tracy: Yeah.
Laura: Yeah. I had a similar comment at a grower meeting in the winter, saying that they weren’t. They had heard that, too, so they weren’t willing to use the aerosols, but we don’t have any data on it.
Tracy: Good question.
Laura: Yeah.
Monique: Sounds like a burgeoning research project. Person in the audience was saying that when there is topography, they were combining the hand applied with the aerosolized.
Laura: No. So we have growers that are using both.
Monique: Oh, find them in those, like, low lying areas. The hand applied.
Tracy: Ah, okay. And was that effective for them?
Monique: Yeah, we didn’t get too far into the actual discussion about if it actually worked or not, but it was definitely someone who was a consultant. I think the next question I have for you guys is, so these thresholds, how did they line up with the predictive degree day model?
Tracy: That’s another burgeoning research project I think we’re gonna need to actually validate. We haven’t done any of that yet. And, you know, with this weird spring weather that we’re all experiencing, how those degree day models especially are lining up, I think, as well, is going to be something we have to kind of revalidate.
Monique: So when it comes to revalidating, what’s. What’s the approach there? Is that, you know, do we need to redesign the model, or is this something that we can just update recommendations based on the current model?
Tracy: So I think, you know, the approach that if we’re able to do this work, we are going to have to probably do some boots-on-the-ground work and possibly tweak the models in a way that makes sense with the flight patterns and with the egg hatch and things like that, that we’re seeing, depending on the species. So I’m not sure what it’s going to look like yet, I don’t know. What do you think at this point?
Monique: I think that we need to think about development and our assumed correlation, that it’s more or less linear.
Tracy: Linear, yeah, exactly.
Monique: They’re not experiencing the temperature linearly. So we’re doing this with ambrosia beetles, but I haven’t really thought about trying it with codling moths. Now, anecdotally, in the lab, we are working with codling moths to try to understand if early exposure to the pheromone can alter their behavior. So exposing them at pupil occlusion, meaning just when the pupa becomes the moth, to see if we can disrupt oviposition or see any behavioral differences. And then I think based on that, and based on conversations with folks in Germany, actually, or from Germany, they’re using nematodes for codling moth and OFM. So, starting to think about what would a spring application of nematodes, followed by maybe a sprayable, followed by the application of the mating disruption tools – could we get even better control?
Tracy: Yeah. I love the idea of entomopathogenic nematodes and trying to use those in the early spring, I think it could be a good, preflight, I think it might be a really cool opportunity, something that we haven’t really tried here all that much, at least with the leps.
Monique: Yeah. So in Germany, that’s actually, I saw a poster at a meeting I was at where they were trying this, and it seemed like it was working. But I think that nematodes, one of the things when you’re working with a whole organism, it’s sensitive. What strain do you have? Making those recommendations would probably take a couple years at least, to make solidly.
Tracy: Yeah. How were they applying the nematodes and where were they applying them? In Germany?
Monique: So they’re spraying, spraying them on the trunk.
Tracy: On the trunk only. Okay.
Monique: Yes. Like, basically doing, like, a ground application where they’re partially aiming at the trunk and also at the ground.
Tracy: Gotcha.
Monique: So, yeah, I think with the, with the leps, it’s, it’s only going to get worse in a lot of ways. I will say, though, that with New York growers, one of the things I’m most proud of this group for is that they have not, like, our chemicals still work. We are not having resistance issues. We looked at over 52,000 fruit last year from a mating disruption study, and the growers, they were well under 2%, sometimes under 0.05% damage. So our chemistries are still working here because they’ve been really diligent about rotating. But that doesn’t mean the chemistries won’t get removed from the toolbox, so to speak.
Tracy: Right.
Monique: Yeah.
Tracy: You know, that’s especially with codling moth with some potentially resistance to diamides, to pyrethroids, to who, you know, and just having the capacity and flexibility, I think, to be able to rotate. So we’re not down to just, you know, one or two classes of chemistry. That’s, that’s my concern as well.
Monique: I think that’s my argument for continuing to talk to Europeans. Not that we don’t want to talk to them, but I think they’re so limited in what they can use that looking to them to see how are they solving these problems before those regulations trickle across the Atlantic.
Tracy: Yeah.
Monique: And get like a framework for what does this pest management program look like with lots of limitations. So, I guess I’ll end on one final question. So what do you think about the overall IPM programs that apple growers are doing? You know, we’ve got to manage diseases and you also have to manage insects, and then there’s managing all the horticultural elements of apple. Is there anything that you see on the horizon that would be most disruptive to current programs?
Tracy: That’s a big question. I’m trying to think what would be most disruptive. I guess what I would say right now, I think what is we’re starting to see be disruptive and could be potentially be more disruptive over time, is just climate change and just erratic weather patterns with drought and water logging, which obviously affects the health of the tree. But also, you know, these temperature extremes and precipitation events also can affect, obviously, diseases in different ways, as well as the insects. So to me, I think it’s just the uncertainty around climate change and how we continue to adapt our IPM programs to ensure sure that they’re climate smart and they can deal with the kind of perturbations that we’re seeing with these changing weather patterns, to me, that I think is probably, what I would say is, I see, is the challenge we can now see, and probably the challenge that I think is going to be looming large going forward.
Monique: So luckily, we have in a USDA SCRI grant to try to answer some of those questions. So, I want to thank any growers that gave us letters for that and hope we get that funded. But I also want to thank both of you for joining me today, and I think that the listeners are going to love this conversation.
Tracy: Thanks, Monique. It was great to see you.
Pathology Updates with Dr. Kerik Cox
All right, it’s practically Memorial Day. Let’s talk about where the apple diseases are and what the season’s been like. It’s been a really cool, almost cold bloom all the way up through petal fall. We got into a little bit of petal fall and a little bit beyond before we started having another heat wave. Typically in the past they coincided side with Memorial Day. This one was a sort of pre Memorial Day heat wave. Last couple seasons have been really cold bloom, post hot bloom thinning period and we’re just probably past or nearly past the thinning period and we’re into that really, really hot bloom weather. We’ve just come down from this heat wave and it looks like for the rest of the week the temperatures are going to be cool overall, with lows in the high forties fifties [°F] and highs in the low seventies throughout the week.
Taking a look at fire blight for the whole season, let’s see what we’ve had. Like I said, cold, warm, warm wet weather after petal fall. It’s typically what we’re seeing here represents what it was like in mid-state, we’ll say with a little bit of a play here and there with the Lake Champlain area being still maybe not entirely 100% petal fall, and the Hudson Valley having a petal fall, but push back into that colder weather around like probably 5/13. Bloom came earlier, later depending on where you were, but sort of mid state, it’s around the 18 April particularly early and really, really, really cold, cold, cold. Nothing to worry about with fire blight until that very end when we’ve had a spike. And most places we’re in the petal fall, maybe Lake Champlain is moving out and as you can see right now where we are on the 26th or something of that, we’re coming down out of the heat wave into cool weather and if you protect it against it, you’re good. Taking a zoomed in snapshot of this sort of thing, you’ll see that the Cougar blight model was into 1200 TRV risk values and moving down into 700, 500, 403 down down to 62. Same with the EIP coming in after a big spike. It’s going to bump back up just briefly tomorrow with the rain. And as you can see, the EIP values are dropping. So, if everything you had was well protected, you should be good to go with the hot weather.
We are at risk for shoot blight, but it’s quickly declining. So with that, what does one do? We’re into that post, that post petal fall period this is a good time to finish whatever’s left of the fire blight season really strong with some prohexadione calcium, about 6oz per hundred. Or if you have a really young block, you can go with the two in one, 2 oz per hundred of the prohexadione calcium with 1oz per hundred of acibenzolar-S-methyl or Actigard.
Right now you’re probably at about the ten to 14 days later. And what we’re trying to do is avoid this awful shoot blight, and this awful row of really young, high density plantings that are completely blighted. Works by sort of thickening the cortical cell walls and the parenchyma, keeping that bacterium from using its awful type three secretion pillus to inject its biomolecular warfare tools, which cause both the organism to spread and cause the disease. And also there’s a feedback loop that has more of the type three secretion system gets activated, it causes the populations to boost, to get more excited. And the next thing you know, they’re becoming systemic. We’re trying to avoid that systemic invasion of shoot tissue. And right now is the last little bit of hot weather before things get really, really cold. And yeah, it’s going to slow the growth of trees, but I don’t think at these rates it’s going to appreciably do it. Would you rather have a slow tree or a dead row of hundreds of young, high density plantings?
So, what you can do after this point, if we keep this cool weather, you can kind of put out the coppers. It’s going to be a protectant. There are organic options, can cause fruit russet, but there are a lot of sort of low MCE coppers as well. And in this case, if you’re in a nursery or in your establishment, you’re not going to worry about damage to the fruit. Um, always when you do this, sort of cool, dry day, we have a lot of cool, dry days, um, seemingly coming up if we can just get past the rain on the 27th. And it’s protectant, it’s only going to get the surface bacterium. And as the terminals grow, you can just outgrow the copper residue. But guess what? You can put it on again. A low rate, a fixed copper program, maybe seven-to-ten day. And if it stays cool, you probably stretch this out to 14-to-21 until you get the terminal bud set, which will be in a couple of months.
And then if you want to prune, if you see fire blight, prune as soon as you can. I’ve started to see a little bit of fire blight showing up in Geneva. No shoot blight, only the earliest stages of blossom blight, but I’m inoculating trees and nothing is moving into the shoots. If I were to want to prune some of that out this coming week, with the sort of low temperatures, low fifties [°F] and the highs of low seventies, probably about your ideal week, once we get past this rain event on the 27th, cool, dry days, what you want to go in and do. We’ll talk a little bit more about pruning later in the season if we get into sort of that area. But you really kind of want to move about twelve inches into the healthy tissue. Um, and this works better in older trees than it does in younger trees. We’ll talk about that as well. If things are getting too close to the main scaffold, you’re probably better off removing and replanting. If you can do more, more intense pruning and you get it all the way, several years of growth into the tissue and take it just like a stub off the main scaffold on some of the larger trees, you can do yourself some, some pretty good in that case.
Now, if you want to try to rescue it and you’re going to save some young trees, I recommend just hitting the 6 to 12oz per hundred of prohexadione calcium, waiting five days, and then prune. And if you stimulate growth with the pruning, you might need to do it again, and you’ll want to keep on that every two weeks until terminal bud set. Now, if you prune it all away, then you should have removed the tree to begin with.
Where are we at with apple scab? It’s pretty much over for this point. We’re moving into the phase where this type of stuff can show up. Apple scab on mature fruit, all resulting from secondary scab and secondary lesions on your leaves as well. Recent years about 2021 to 2023, about less than five inches rain easy apple scab season. The last big one, I’d say, was 2019 with about 15 [inches of rain]. And this one we’re moving into about eight inches as of June the 1st, or if you will, coming into June the first with this last little bit of rain that’s predicted. And SDHI fungicides remain very effective for scab, a little harder for mildew. And it’s also important to note, as we’re moving into these drier seasons, this drier post-bloom weather, particularly like in 2020, 2021, we had crazy pressure for powdery mildew. Now, in this case, we’ve had a good bit of rain up front. Fungi do like rain and water, and mildew needs some, but it doesn’t like free moisture. So we’ve gotten all the adequate moisture that we could possibly have. At this time, we’re going into a nice dry period, which the powdery mildew, if the infections have occurred, will really, really enjoy and can cause sporulation and trouble.
So what’s it look like for apple scab? Um, not every place looks like this with a sort of combined wetting event over the rain. We got the last night [Sunday May 26], today [Monday May 27] moving into the rain, coming up for the week. All the ascospores are long gone. We’re talking mostly about secondary infections now. But I wanted to show this graph because I wanted to point something out. You might notice that on the 25th, it says combined with the 26th, it said, yes, it’s very sunny today on the 26th, and now it’s saying combined again on May 27 with another moving into May 28. And so one of the things that it notices, if you see a lot of combined and then combined, combined, combined, combined. Yes, that’s one contiguous period. Now, what’s really important in this case is we’re getting into warmer weather. We’re in the seventies. We’re hotter. Apple scab hates this. And while it looks like one massive period with a combined yes and another combined yes moving into the 28th, what’s really happening is, because it called it here, there is more than 24 hours of drying between that yes and the next line. Apple scab is getting baked right now. And so what I wanted to suggest is that this period, while it looks like a massive all day rain event for four days in a row, is really, really not, it’s two periods with more than 24 hours of dry, blazing, sun scorching weather that’s probably killing your apple scab. So in this case, it’s not necessarily cause for panic. Would you want your crop covered? Yeah, but it’s not too much of a cause of concern at this point.
What about powdery mildew? I’d say probably last week and maybe the week before that, with all the rain, we’ve gotten enough growth and enough tissues have burst forth with powdery mildew. And you’ll see these primary shoots, and they may be a blossom cluster like I typically see in my Ida Reds, or they may be the very start of a new first year shoot that just erupts and is covered with powdery mildew. And then these things will lead to the unfortunate situation of lesions on secondary leaves. And of course, if this builds up, a lot of fruit russets that we have. And so these things are showing up now they’re present. We’re going into a hot, dry period. It’s time to start thinking a little bit about mildew. And what is all this netting? It’ll make a netting type russeting on the fruit in this particular instance. And these are failed conidial infections. It wants to get apple tissue, fine, but it’s like, oh, that’s not a leaf, and it’s just a mess and it stops. But what it does do is ruin your fruit. It won’t necessarily sporulate on your fruit like in other systems, like strawberry or other things inside covered production agriculture, but it will sporulate on the leaves. And these can come out and continually infect and cause new infections as the terminals grow and can end up damaging your fruit in turn. So with warm, dry weather, these powdery mildew epidemics can explode. I’ve seen a good bit of primary infections. These either blighted shoots or blighted flower clusters, and some of my older, unmanaged blocks here in Geneva, they’re ready to start exploding and causing secondary infections. A lot of the cultivars that we like to use are, you know, maybe more selected for resistance to scab or other factors or for taste, storeability and color often get powdery mildew, particularly up along the lake. And one thing to note, if you have cultivars and it says “resistant apple,” they, what they typically mean is apple scab resistant. The two sources of resistance are not in any way remotely linked whatsoever. And even if you have apple scab resistance, you can completely get blighted by powdery mildew. And if just goes on unmanaged in the summer and you’re not applying a lot of fungicides from this point into the early parts of summer, the powdery mildew can become completely unchecked. And it looks like you might be having Christmas in July, as if you sprayed your plants with fake snow.
So what do we know about fungicide resistance? We did some extension surveying with one of my last students, David Strickland, and he found that surveying several years through 2022 suggests that populations are sensitive to most of the single site fungicide tools that we would like to use. So that’s good. What do we know about fungicides at this point in time? Right now, Captan and Mancozeb are ineffective and may not be the best tools that we have as we’re coming out of the thinning period in general. Mancozeb fine, maybe not so much Captan, we’ll talk about that very briefly at the end. DMI fungicides less effective than they might have been in the nineties. One or two applications would make it seem like powdery mildew was never of concern. They’re still the best fungicide group to use, and some of them are quite effective. The QoI fungicides we’ve had a lot of concerns around the turn of the century, 26 I mean 2006 through about 2012 for resistance to apple scab, but they still remain very, very effective against mildew and I would say falls into my category of best fungicide group with the DMIs. I might even like these a little bit better than the DMIs for powdery mildew at this stage. SDHI fungicides – some are particularly good at getting powdery mildews, others are not, and it typically involves with how soluble these things are. The more water soluble, I’ve noticed the DMI fungicide and QoI fungicides, the more effective they are against mildew and the more easily they are overcome by resistant apple scab. So it’s kind of a balancing act between the two types of diseases and fungi. And if this becomes a bigger problem in scab because we get too much hot and dry weather, probably change my recommendations for which DMI fungicides and QoI fungicides to use some of the combo units that have a group seven fungicide and them and the QoI fungicide are some of the best materials for wiping out powdery mildew. You can also do frequent sulfur applications, which actually might be okay at this time of the year if our temperatures are staying under 80. You’re not going to get as much sulfur injury at this time and could be a reasonable management tool if you want to use it. However, it can irritate your eyes and, um, make the orchard less fun to work in than some of these other types of things. And we’re at the period right now we’re near late bloom, the late petal fall, moving into third cover is incredibly important for going after the powdery mildew. This seems to be the hot zone of time around the Finger Lakes and in some of the other regions for sort of getting this and squishing it. I don’t think you have to go as early as, um, early bloom or tight cluster as well. I think I would save my applications for now for another reason I’ll talk about a little bit later when we get into the apple blotch / Marssonina scenario. It looks like those time periods are also good for that path of system which is coming up we’ll talk about in a little bit later.
And then speaking of Captan not being effective against mildew at this particular time, we’ve had a lot of prolonged wet weather and we’re finally getting a break from it. For the most part. It’s going to be a cool week, but we might have some thunderstorms and trees are beyond petal fall. But I would say for just another week or two until we’re well past the thinning window, let’s take caution with Captan. If we get cold weather, if we get overcast weather, and again, humidity tank mixing Captan with foliar nutrients and various spray adjuvants and other fungicides that might have just a little bit of oil in it could end up causing some severe fruit finish damage, spotting and necrosis. And the Captan can very well enhance the penetration, or these adjuvants can enhance the penetration of Captan. And once Captan gets inside the tissues, that’s where the damage ends up being caused. And anytime you go out there with any slower drying conditions, high relative humidity, thunderstorm, light rain, overcast skies, the potential for fruit finish just gets a little bit higher as the tank mixes get more and more complex, if you will, particularly when the trees have young, susceptible tissues. And we’ve been generally recommending no more Captan till at least second cover, and if you want to go back in afterwards, you still might need to take caution as some varieties seem to be a little more sensitive to it in the big tank mixes. So if you need a material for resistance management while we still have time around that 72 day PHI, use Mancozeb for your variety and you can use sulfur. I think in this case that’s helpful against powdery mildew as your protectant to put in with other things. And it can also cause problems in complex tank mixes, but at least the weather is going to be a little cooler. If you’re able to put fewer things in the tank, go sulfur. If it’s going to be quite complicated, I would even consider using a biological if you feel like you need some resistance management. Will you cause resistance if you leave out the protectant altogether? No. You can easily make about one to two to maybe three or four applications of a single site fungicide alone, these QoIs, the DMIs, the SDHIs, all by themselves, and you’re not really going to risk the development with just a few applications. Now, do you have to follow the label and put a protectant in? Absolutely. But I wouldn’t stress out over the protectant, or put in a protectant that’s going to cause damage. And any, I mean, even a little bit of escape on apple scab is less than a complete crop loss due to damage. I don’t think we have to worry so much about Captan now, given the weather we have, but maybe just for another week. If you can avoid it as you’re getting there and you finish up thinning, it’s probably the best. And with that, I’ll talk to you later.
State of the State with Dr. Anna Wallis
And now for the state of the state, your weekly roundup of phenology and degree day accumulations from major food production regions of the state. I’m Anna Wallis with the New York State IPM program at Cornell, and the information I’ll be sharing as usual, has been aggregated from the regional specialists, including Mike Basedow, Janet Van Zoeren, Mario Miranda Sazo, Craig Kahlke, and Dan Donahue. It also includes my own observations and information collected from NEWA.
So far, the month of May has been near average or above average for both temperature and precipitation. We had a really warm trend last week and slightly cooler trend this week. Precipitation varied for most of the state from about a half an inch to three quarters of an inch, which was mostly received on Wednesday last week and Monday of this week. The six-to-ten-day outlook looks like warmer and above average precipitation across the region. Looking at phenology across the state now, we continue to be well ahead of the 15- and 30-year degree day averages across the state, partly related to the early spring and also related to the warming trend last week. Hopefully it’ll slow down just a little bit this week, but we continue to have predicted above average temperatures, so things will continue to move along. Thinning continues across most of the state right now. In the Hudson Valley, we’re approaching the end of the thinning window with fruit sizing 20 or more millimeters in diameter, depending on the variety and the location and how much thinning has been done. In western New York, things are similar, approaching the end of the thinning window. In the Capital Region, just a little bit behind, in many varieties and locations, fruit is approaching that 20 millimeter size as well. And in the Champlain Valley, fruit is somewhere between 10 to 15 mm in diameter. And so right in the crux of the thinning window.
Looking at some upcoming pest events and activity, most people are managing plum curculio at this time. We saw more of it active in unmanaged locations in stone and pome fruit last week, the beginning of this week, it likely moved into orchards across the state last week in the warm spell, just a couple of warm nights is enough to move it from hedgerows into the edges of orchards, so that’s a great place to be scouting. With the first cover spray on, additional sprays will be needed based on how warm conditions are, and that could be up to two or three sprays. So you can pay attention to the degree day model and plum curculio model in the NEWA online platform to help you predict how long to be covered. You should remain covered for up to 308 degree days base 50 past petal fall. This is a really important time to remember to change your phenology dates when you’re using any of the new models. So when you’re looking at each model, it will ask you for your green tip or your petal fall date, and you should change those appropriately. We found that they are not very accurate in many locations this year.
Looking at some of our lepidopterans, oriental fruit moth flight is ending. It’s been very variable whether we’re even detecting this insect dependent on location. Not all sites seem to have an active population. Codling moth sustained trap capture was recorded in some locations. In other locations, again, it’s been spotty, so we don’t always have trap captures at some locations. In the Hudson Valley, the first moths were on May 13. That’s at the Hudson Valley research lab. Similar in the Lake Ontario region and the Capitol Region. So that’s the most appropriate biofix for first moths on May 13 or about that time. Again, it’s important to be looking at specific flights in your specific location because it can be variable. And then the Champlain Valley looks to be about a week behind that. Based on that information, we’re approaching the threshold for an insecticide targeting larvae, which would be at 200-to-250-degree days base 50, which might be around the end of the week. But again, that should be based on trap captures at your site and degree day accumulations.
Oblique banded leaf roller first trap capture was recorded last week at the Hudson Valley Research Lab and at several sites in western New York and the Capital Region. Again, it hasn’t been reported at every site where we’re monitoring, so be paying attention to your location.
We’ve seen some activity of green and rosy apple aphids, but not a considerable amount. Probably most of that has been taken care of with the first cover spray.
Dogwood borer was detected at a few locations, the adult flight both in western New York and in the Hudson Valley and in Ithaca. So be careful with your identification on this pest. You can also capture peach tree and lesser peach tree borer in the same trap. And all three of these insects are clear wing moths, so it’s important to be paying attention to the banding on those insects, the size of the insect and the color.
Woolly apple aphid continues to be active. Again, this is location dependent. We’re seeing it primarily on pruning cuts, older pruning cuts inside the canopy, so be sure to be looking closely inside the canopy when you’re scouting for that insect.
You can also be looking for leaf hoppers, mites, and sawfly damage. We’ve seen a little bit of activity of all three of those insect pests over the past week as things have warmed up.
Moving on to diseases, fire blight continues to be a risk wherever blossoms are present, so continue to be watching those models. Primary scab for apple scab season is mostly over in many places across the state. We’re now detecting abundant lesions in unmanaged blocks, so we know that there is plenty of inoculum in those types of locations for secondary infections. We are seeing a few locations in managed orchards where a few lesions are present, so primary scab maybe was slipped through a little bit, so make sure you’re being vigilant of that. We’re continuing to see powdery mildew in many locations. This is the disease we sometimes call the fair-weather disease. It favors warm, humid, but dry conditions because it can’t survive in standing water. So we expect with warm, drier conditions we might see more of this, this pathogen.
Moving a little bit into cherries and berries we’re starting to think about fruit flies and we’ve started putting out our traps for spotted wing drosophila in many places across the state. With the early warm season and wet conditions, we’re predicting that it might be an early emergence for this fly, and so we continue to be vigilant for that. As we’ve said in the past, both jar traps and sticky red cards seem to be viable options for monitoring for this pest, so you have options, you can be monitoring either with those jar or drowning traps or with the red sticky cards. This year, we’ll be sharing information about spotted wing drosophila on a new blog, the Berry Pest monitoring network blog. So we’re asking everyone to subscribe and confirm their email on the new site. If you’re already subscribed to the spotted wing drosophila blog, you would have received an email about a blog post that asks you to subscribe and move over to the new blog. We’re doing this for a couple of reasons. The first one is that we’re continuing to monitor spotted winged drosophila, but we’re also starting to monitor some other berry pests including cranberry fruitworm, cherry fruit worm and blueberry maggot, which were top insect pests identified from grower surveys in the winter of 2023 and 2024, both at meetings and on the blog through a survey. Our reporting will also be more regional instead of limited to county, which will account for regional microclimates. And finally, it will make it a little bit easier for us to manage. We can manipulate data a little bit easier on the back end, which should hopefully be invisible to you, but it will help us serve the industry a little bit more efficiently. At this time, we’re recommending that cherry growers subscribe as well in order to stay updated on the spotted wing drosophila first detection and sustained detection. We will, over the transition, try to post on both sites to make sure that no one’s lost and no information is missed. But please move over to the new blog as this is where we will primarily post the most up to date information.
And now here are the current degree days in major fruit producing regions of the state. Throughout the season we’ve been aligning this information with previous work that was done by Art Agnello relating to McIntosh phenology and degree days using base 43 Fahrenheit. In Geneva, we’re at 906; in Highland at the Hudson Valley Research Lab 965; Clifton Park 844; Peru 704; Medina, an inland site 889; Appleton North, a lake site 770; Fairville, an inland site 841; and Williamson, a lake site, 833.
That’s all for now and good luck until next week.
| McIntosh Phenology and DDs (43F BE) (avg +/- std) | |
| Phenological Stage | DD Accumulation |
| Silver tip | 58-106 |
| Green tip | 99-144 |
| Half-Inch Green | 150-201 |
| Tight Cluster | 206-257 |
| Pink | 267-316 |
| Bloom | 344-415 |
| Petal Fall | 439-523 |
| Phenology & DDs for NY NEWA Stations from 1/1 – 5/27 | ||
| Station | DD Accumulation | Stage |
| Geneva | 906 | Fruit Set |
| Highland (HVRL) | 965 | Fruit Set |
| Clifton Park | 844 | Fruit Set |
| Peru (Forrence) | 704 | Fruit Set |
| Medina – Inland | 889 | Fruit Set |
| Appleton North – Lakeside | 770 | Fruit Set |
| Fairville (The Apple Shed) – Inland | 841 | Fruit Set |
| Williamson (DeMarree) – Lakeside | 833 | Fruit Set |
Phenology & DDs for NY NEWA Stations from 1/1 – 5/27
Station || Stage || DD 43F
Geneva || fruit sizing || 906
Highland (HVRL) || fruit sizing || 965
Clifton Park || fruit sizing || 844
Peru (Forrence) || fruit sizing || 704
Medina – Inland || fruit sizing || 889
Appleton North – Lake || fruit sizing || 770
Fairville (The Apple Shed) – Inland || fruit sizing || 841
Williamson (DeMarree) – Lake || fruit sizing || 833
*all DDs Baskerville-Emin, B.E
Upcoming Pest Events
Pest/Phenology Event || DD Base 43˚F || Approx. Date
Petal fall (McIntosh) || 479 ± 42 || 18-May ± 6 days
Lesser appleworm – 1st flight peak || 569 ± 205 || 22-May ± 13 days
Plum curculio – 1st oviposition scars observed || 555 ± 77 || 25-May ± 9 days
Pear psylla – hardshell stage observed || 569 ± 87 || 22-May ± 9 days
Lesser peachtree borer – 1st adult catch || 570 ± 94 || 24-May ± 8 days
San Jose scale – 1st flight peak || 644 ± 89 || 29-May ± 8 days
ERM Sample – 2.5 mites/leaf || 1-Jun
OBLR traps set out || 1-Jun
Black stem borer – 1st flight peak || 681 ± 170 || 1-Jun ± 9 days
RBLR – 1st flight ending || 753 ± 140 || 2-Jun ± 8 days
American plum borer – 1st flight peak || 784 ± 183 || 3-Jun ± 9 days
Codling moth – 1st flight peak || 768 ± 206 || 3-Jun ± 12 days
STLM – 1st flight ending || 813 ± 128 || 5-Jun ± 9 days
OBLR – 1st adult catch || 884 ± 90 || 9-Jun ± 6 days
OFM – 1st flight ending || 825* ± 126* || 12-Jun ± 8 days
Peachtree borer – 1st adult catch || 1032 ± 266 || 15-Jun ± 11 days
San Jose scale – 1st flight ending || 1039 ± 182 || 16-Jun ± 8 days
Black stem borer – 1st flight ending || 1056 ± 198 || 19-Jun ± 9 days
STLM – 2nd gen. 1st adult catch || 1063 ± 91 || 16-Jun ± 6 days
San Jose scale – 1st crawlers observed || 1124 ± 91 || 19-Jun ± 8 days
Dogwood borer – 1st adult catch || 964 ± 230 || 12-Jun ± 9 days
American plum borer – 1st flight ending || 1344 ± 144 || 29-Jun ± 7 days
*Base temperature for OFM 45F
NEWA Fire Blight Model update – Effects of streptomycin application up to 5 days in the future. https://blogs.cornell.edu/enychp/uncategorized/update-to-newa-fire-blight-model-streptomycin-applications-5-days-in-the-future/
NEWA Help Desk Frequently Asked Questions and Table of Contents. https://help.nysipm.org/hc/en-us/categories/16994462926231-NEWA-Network-for-Environment-and-Weather-Applications
Quick Guide for Apple Insect Pests https://help.nysipm.org/hc/en-us/articles/23290226665751-NEWA-Quick-Guide-for-Apple-Insect-Pests
NY Tree Fruit Pest Monitoring Network
https://blogs.cornell.edu/treefruitpests/
Interested in collaborating and contributing trap capture data? Contact Anna Wallis aew232@cornell.edu
Berry Pest Monitoring Network – NEW Blog!
https://blogs.cornell.edu/berrypests/
Quick Guides for SWD Management