Dr. Gary Grove presents an update on sweet cherry powdery mildew with an introduction of the disease, epidemiology, and current situation regarding pesticide resistance in Washington State. This talk is part of the WSU-OSU Tree Fruit Webinar series lead by Ashley Thompson, Matthew Whiting, and Bernardita Sallato. This session was hosted by Bernardita Sallato, WSU Tree Fruit Extension.
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| Okay, many of you have heard me cover this again, cover this many times in the past years, but we’re in a different situation coming into this year. And I thought I’d update you on our current status, largely of our fungicide arsenal. So one thing that’s different in the last year and a half, we did change the name of the pathogen that causes cherry mildew to Podosphaera cerasi. You can still call it clandestina if you prefer that. | Title slide. Presentation Title: Powdery Mildew of Cherry (caused by Podosphaera cerasi). Presenter information: Dr. Gary Grove, Plant Pathology Professor, Washington State University. |
| What I’m going to cover today is just a very brief background on the pathogen and the disease, basic management recommendations, but I’m really going to dig deep into the fungicide situation. Some background information, the resistance situation that we’ve found as a result of a research program, a generalized industry response to the situation that we’re in. And keep in mind as we go through this, I fully realize that we’re juggling a bunch of different balls in the air when we try to respond to do this. So at the end of the day, my advice is basically just do the best you can with the tools you have. And then I’ll catch up on some other items at the end. | Slide titled “Fungicide Resistance Response” contains a bullet point list of the key topics of the presentation, as outlined in the audio. |
| The fungus that causes the powdery mildew produces two spore types, ascospores and canidia. The ascospores are born in what are called chasmethysia, and the chasmethysia are these small, they are barely visible to the human eye, these small brown to black structures that are formed well into the epidemic. And this is actually the sexual stage of the fungus. It’s a source of genetic variability, but it is the only means of overwintering, that is getting our powdery mildew friend from year one into year two. The ascospores initiate the epidemic, and keep in mind that this is the only phase of the disease cycle that requires free water. The second spore type, our asexual spore, the canidia, do not. They carry their own water within the spore. | Slide titled “Chasmothecia and Ascospores” contains a photo of the white coating of powdery mildew on a plant leaf, and a microscopy photo of the fungal spores. Text below outlines that the sexual stage allows for genetic variability, the spores can overwinter and initiate epidemics, and that they require free water. |
| Okay, one thing about chasmethysia, if you have a lot in the wintertime going into the next season, high amounts normally mean that early season control is more important than say a normal year. Keep in mind that 2017 was our last real industry-wide hammer. We’ve had several years, you know, you can find mildew, but what I consider a hammer is something that’s industry-wide and something that brings the industry to its knees. So we haven’t had one of those catastrophic years in quite some time. So vis-a-vis overwintered inoculum, I’m sure there’s enough out there to get an epidemic started, but in terms of numbers, we’re probably in pretty good shape compared to what we were in 2018. | Slide titled “Overwintering Inoculum” contains a microscopy photo of the dark brown chasmethysia on the surface of a leaf. |
| This is your typical powdery mildew on foliage. If you deal with cherries, you’ve all seen this, but once you get to this stage, this white to grayish mealy coating, it’s actually the fungus producing its second asexual spore type or secondary asexual spore type called the canidia. And it’s this phase that’s responsible for the spread and the intensification of the epidemic. So the ascospores, when they’re released for the chasmethysia, initiate the epidemic, but the canidia spread and intensify it. | Slide titled “Foliar Mildew” contains a photo of the typical white coating of powdery mildew on a plant leaf. |
| This is just a drawing of a powdery mildew on a leaf surface. They’re superficial. The actual strands of the fungus that are growing horizontally are called hypha, and they stick a peg down into mesophyll cells with what’s called an haustorium, which sucks nutrients out of the host. And then the vertical structures are what are called canidiophores. And about once every 24 hours, a new canidium is produced at the apex of the conidiophore. And without the intervention of control measures, this can keep happening throughout the growing season. And keep in mind, this is a very highly magnified drawing. But keep in mind, you can have probably half a million canidia produced in any 24-hour period in a piece of leaf tissue that’s the size of a quarter. | Slide titled “Canidia (Asexual Spore)” contains a drawing of the asexual spore structures on the surface of a lead, They are branching and interconnected horizontally with vertical structures coming off of the branches. |
| These spores, once the disease gets rolling, are produced in profusion. They’re airborne. They can travel distances via air currents and wind. Now, in terms of distance, you can get significant travel. Say you have a severely infested cherry orchard, you’ll have a significant amount of canidia that are dispersed over a horizontal distance of about between 100 and 200 yards from there. But these canidia can get up in the air and travel quite long distances in the air when conditions are good. And for example, canidia of Erosyphae nicator, which is the grapevine powdery mildew fungus have been trapped in the air over the English channel. So the infested grapes were obviously in France and the spores were caught in the air between France and Great Britain. So they can travel great distances. The important thing to remember about this phase is that it does not respect fences or property boundaries. In other words, if you have an infestation of mildew and you have a neighbor that has an orchard adjacent to yours, what’s going on in your orchard vis-a-vis resistance because of this means of dispersal definitely apply to your next door neighbor. | Text reminders appear on the slide that the spores are airborne and do not respect property boundaries. |
| So to summarize the disease cycle, again, we’re up here right now. And I put a circle around it just to again, remind you that we haven’t had a severe industry-wide epidemic in several years. So in terms of what we’re dealing with on the fungicide challenge that we’ll get to here in a bit, we’re in pretty good shape compared to where we were in 2018 at this time. In other words, normally following a severe epidemic year, your risk for early infection is higher the following year. So again, Those chasmethys and ascospores initiate the epidemic, fly up to leaves where the secondary spore type or canidia are produced. This phase can continue throughout the season, either until intervention occurs with fungicides or some other means, or dormancy occurs. So again, primary infection, secondary infection, repeating cycle, and then as the colonies age on the foliage, the chasmethesia are produced and that completes the disease cycle. | Slide titled “Cherry Powdery Mildew Disease Cycle” contains a diagram of the disease cycle. There diagram is circular with red arrows and images indicating the disease stages throughout the year. A circle indicates that we are in the dormant stage. |
| So general management tips here, and I’m just going to go through this list. I’m not going to beat anything to death until we get to the fungicides. But again, pruning, suckering, irrigation delay. We found in many years in the absence of significant spring moisture that the initial irrigation set, if it’s sufficient to wet the trunks, can actually incite the spore release that results in primary infection. So if you delay this, it actually delays the initiation of the epidemic. And in theory, if delayed it long enough, it could shift the exponential phase of the epidemic to post-harvest. So it would reduce risk to your fruit. | Slide titled “Disease Management” contains a photo of a cluster of cherries showing white mildew, and a bullet point list outlining the disease management approaches. |
| Fungicide programs. There’s the approach. And the approach we use is largely one of protection. That is protect young foliage and young fruit or developing fruit. The reason I stress protection here is it’s far easier to protect against powdery mildew than it is to get rid of it once you have it. So the protection is the approach. We also suggest that the synthetic fungicides that pose a resistance risk, these be used in a protective fashion. And the reason there is, is that if you’re protecting against mildew, you’re not exposing as many individuals in the mildew population to selection pressure. | The presenter remains on the slide as he elaborates on each disease management approach. |
| Application, this is extremely important. Calibration is important. You really wanna know how much you have in the tank, how much active ingredient. You also wanna make sure that you’re getting the recommended dose of the ingredient to the host. Coverage is extremely important and spraying under good conditions is extremely important. | |
| And what I mean by conditions, I live in West Richland and in the springtime when I’m driving the interstate up to Prosser, it hasn’t escaped my attention, particularly in vineyards that I see an awful lot of spray going up in the air on windy days. And when it gets up in the air a little ways, it becomes horizontal. And I don’t know where it’s going, but I can tell you it’s not going on the adjacent vines. So it’s important to get the fungicide to where you want it to do its business. And then of our available compounds, resistance management. | |
| And by and large, our industry has done a really good job of resistance management over the years. We started using resistance management prone compounds back in 1988. And we have a resistance, a pretty serious resistance problem right now. And frankly, I think it’s a tribute to the industry that we haven’t had a very severe situation like this long before this. So by and large, the industry’s been very cognizant of preserving our fungicide arsenal. Fungicides come in a wide variety of shapes and sizes, some control mildew, some don’t. | Slide titled “Fungicides” contains photos of five different containers of commercial fungicide. |
| But to put things in a historical perspective, and keep in mind, I came to WSU in the fall of 1986, and Ronald Reagan was still president then. And I didn’t know what I was going to work with right away when I got to WSU. My first day at work, October 1st, I came in and I when I was walking down the hall to my office, I noticed that my office door was open and the light was on. And I went to go to my office and there’s a middle-aged man sitting there, a very friendly fellow. And he stood up to me and said, hi, I’m Tom Matheson and I’m with Stemilt Growers and you must be the new mildew guy. So that’s how I got started working with cherry mildew. | Slide titled “Fungicide History in PNW Cherries” contains a timeline from 1986 to 2016 with labels for years in which a new formulation was made available for treating mildew. |
| But back in 86, the only thing that we had registered for mildew control was sulfur. And we only had 10,000 acres of cherries at the time. So in 88, we saw our first DMI or group three fungicides. That is, we used to call them sterile inhibitors. We incorporated HORT oils into the programs in 92. The QOIs or strobilurins group 11s became available in 96. And again, this drawing is not to scale. 2001, quinoxyfen, our only group 13 compound, became available. The SDIs, generally around 2010, those are the group sevens. And then we have several new modes of action that have become available during the last several years. So essentially, we have gone from Reagan to Biden. As you know, there’s a lot of time and people in between there. So that’s a bit on the history of our fungicide spectrum in cherries. And believe me, even with the resistance problem we have, we’re still in a lot better shape than we were in 86. | |
| So a bit about chemical names. Chemical name, it’s just given to a group of chemicals that share a common biochemical mode of action and may or may not have similar chemical structures. And the mode of action refers to the specific cellular processes that are inhibited by the fungicide. | Slide contains the definition of a chemical group or class and a fungicide mode of action. |
| So some different modes of action for our mildew fungicide. Sulfur inhibits spore germination. The DMIs or Group 3s inhibit membrane synthesis in the fungus. The SDIs inhibit respiration. The QOIs or Group 11s also inhibit respiration, but they do it in a different place cellularly. U13 inhibits the formation of haustoria. Again, the haustorium is that structure the mildew puts down into the leaf to steal nutrients from the host. The quinolines or Quintec, group 13 inhibit appressoria formation. Appressoria is a little platform. The fungus forms when it’s trying to get into the leaf on the leaf surface and without which it can’t get into the leaf surface. And then mineral oils disrupt cell walls and interfere with host contact. | Slide titled “Fungicide Mode of Action” contains text showing the modes of action of several groups of fungicides, as outlines in the audio. |
| Okay, there’s another phenomenon. I’m gonna try to move something around on my screen here. I have a distraction. Okay, fungicide site of action. This is really important as we proceed because it’s how the different FRAC groups have been constructed. The target sites are specific enzymes in a cellular process to which the fungicides are binding. So in terms of the group 11s, the QOIs or strobilurins and SDHIs, group 7s, they both inhibit respiration or the Krebs cycle. So they have the same modes of action. But how they do this, they do this each in a different manner. They inhibit respiration, the 11s inhibit respiration through cytochrome complex III, whereas the SDHIs do it through cytochrome complex II. They have different sites of action. And let me see here. | Slide titled “Fungicide Site of Action” contains an example of a fungicide label, with it’s FRAC group highlighted. To the left is text defining targe sites and outlining the different modes of action for the mentioned fungicides. |
| So the mode of action is how a fungicide conducts this business, and again, the group 7s and both 11s inhibit respiration, for example. And the site of action is where those fungicides actually conduct their business. And looking at it on a cellular level, again, the mode of action of both the 11s and the 7s is the same. They inhibit respiration. But one group inhibits cytochrome complex III. The other inhibits cytochrome complex II. So they both inhibit respiration, but they do it at different sites. | Slide titled “Modes and Sites of Action” contains an example of a fungicide label, and text highlighting that mode of action is how a fungicide works, while the site of action is where a fungicide works. |
| And looking at it on a cellular level, again, the mode of action of both the 11s and the 7s is the same. They inhibit respiration. But one group inhibits cytochrome complex III. The other inhibits cytochrome complex II. So they both inhibit respiration, but they do it at different sites. | Slide titled “Fungicide Mode and Sites of Action” contains a diagram of a cell in which a group 11 fungicide is inhibiting cellular respiration via cytochrome complex three, while a group seven fungicide inhibits respiration via cytochrome complex two. |
| So that’s where the fungicide resistance action committee comes in. It’s called FRAC. And the URL is at the bottom of the page. And there are actually several different ways to get here. You could use that, or you could use frac.info. But the Fungicide Resistance Action Committee, it’s an international organization comprised of plant pathologists that work in both the academic world, government, and in private industry. And they’ve broken the FRAC groups down into committees whose responsibilities are specific different fungicide sites of action. | Slide titled “Fungicide Resistance Action Committee” contains an image of the homepage of www.frac.org. |
| For example, there’s a group for the group threes, there’s a group for the group sevens, group 11s, et cetera, et cetera. So that number you see on the label of a fungicide, and I just use Quash here as an example, where it says group three, that means its site of action is group three, and the three is the FRAC code. | Slide titled “Fungicide Site of Action” contains an example of a fungicide label, with it’s FRAC group highlighted. |
| Resistance development, there’s two different types. There’s directional and disruptive. And again, if you look at resistance development over time, the far left is today and the far right is down the road. When you first expose the population to the fungicide, the population is comprised largely of fungi that are susceptible to the fungicide. But there may be a few resistant individuals in that population. Under continuous selection pressure from that site of action, gradually the proportion of resistant individuals in the population is going to increase. So over time, without mitigation and with continuous selection pressure, the number of resistant individuals in the population really increases. | Slide titled “Resistance Development” contains a graphical illustration of resistance developing in a fungicide population after fungicide is applied. Susceptible fungi are orange, and resistance fungi are black. The resistant fungi survive the fungicide application and therefore increase in number over repeated applications of the same fungicide. |
| Two different types, directional and disruptive. I’ll go with the disruptive first. This would be characteristic of the group 11s. And this is a situation where nearly all individuals in the population are susceptible to the fungicide when it’s first introduced, but a few are immune. And then all of a sudden it just collapses. The proportion of the resistance increased with selection pressure. This is characterized by a very, very rapid loss of control. And there is cross resistance with this type of resistance, particularly in the group 11s. | Slide titled “Types of Fungicide Resistance” contains text descriptions of directional and disruptive fungicide resistance, as outlined in the audio. |
| Now the other type of resistance, and we’ve been over this before years ago with the DMIs is directional or what I would call shades of gray. The response to the chemical is dose dependent and selection pressure pushes the least lethal dose higher over time. And this is the type of resistance we see in the group three’s DMIs or sterile inhibitors. And these can, resistance can be overcome by raising the rate. But keep in mind, you get to a point where you have to go off label with the rate to get good control. So that’s no longer an option. | The presenter remains on the slide as he elaborates on each type of fungicide resistance. |
| But this is characterized in the field by a gradual loss of control. That is, you think your mind’s playing tricks on you, where you have a favorite DMI compound. And we really saw this early in the our chemical history with things like Rally and Rubigan. When they first came out, they were just amazing. In fact, I was such a fool that right after we got Rally labeled, I said at, I think it was at the Cherry Institute, I said that our problems with mildew are history. That’s how well it worked. Well, here we are 20 some years later and I’m still talking about mildew. So I was really wrong there. But over time, I started having people contact me saying that, hey, this doesn’t seem to be working like it used to. I’m still getting control, but I have to spray more often or I have to keep raising the rate. Well, that’s a really good indication that the population’s shifting. And if you’re the person in the orchard day to day and you see this with your own eyes, don’t think you’re going crazy. Take a look at the components of your spray program. | |
| So looking at this in terms of population, the number of colonies is on the vertical axis. And here’s the qualitative resistance is very, very sudden. This is the group sevens and group 11s. One sprayed time it works and works quite well. And then it all of a sudden collapses. It’s just that the resistant individuals totally take over the population. With the quantitative, it’s more gradual, and it’s a gradual shift from a predominantly resistant to the compound population, or I’m sorry, sensitive to the compound population to a resistant to the compound population. | Slide titled “Types of Resistance” contains graphs of the number of individuals versus fungicide sensitivity in qualitative and quantitative fungicide resistance. The qualitative shift is sudden, with a large peak in resistance, and the quantitative is more gradual in its shift towards a resistant population. |
| Okay, and there’s cross resistance. It’s pretty well understood in the group 11s. If you get resistance to one member of the group 11 group, It imparts resistance to all members of that FRAC group. So for example, if you get resistance to GEM or Trifloxystrobin, you’re also going to get cross resistance with Cabrio or Pyroclostribin. It’s also present in group three, but it’s less well-defined and understood due to the quantitative nature of the resistance. | Slide titled “Cross Resistance” contains text defining cross resistance and the FRAC groups in which it is present. |
| So now where the cross resistance is really important is when we start talking about fungicide choices. And as you know, some of our best fungicide choices for powdery mildew are premixed formulations of different FRAC groups. So let’s go back to GEM or Trifloxystrobin. And again, the 11 in there is the FRAC group. If we get resistance to Trifloxystrobin, it’s obviously also resistant to these trifloxystrobin of fluopyram. And with Pristine, there’s also cross-resistance. So there’s also resistance to the pyroclostribine component in Pristine. So remember, part of the rationale for using these premixes is that there’s two different modes of action in them. And when they’re fresh off the shelf, the mildew is sensitive to both mode of action. So you have built-in build-in resistance management. Okay, if one of these no longer is effective against powdery mildew, but you’re still using it, the seven component in the case of Pristine is boscalid and fluopiram with Luna sensation. It is still effective against mildew, but you’re not tank mixing it or using a pre-mix and managing resistance to it. | Slide titled “Cross Resistance (Group 11)” contains a diagram of the how resistance to one group 11 fungicide can impart resistance to other group 11 fungicides and components of premixes containing multiple FRAC groups. |
| I always thought that the premixes, I liked them because they had built in resistance management, but I was always concerned about a situation like this. And again, all the 11s, if you get resistance to one, all the 11s on that page are resistant. For example, if you have used GEM exclusively from this group and you have resistance to Gem and you’ve never used Cabrio or Pyraclostrobin, there’s also resistance to Cabrio or Pyraclostrobin. | |
| Okay, I’m not going to beat this to death, but the cherry powdery mildew pathosystem is a very, very high, a very, very high fungicide resistance risk pathosystem. We have to spray multiple times. Epidemiologically, this disease can be very, very explosive. It has a very, very high reproductive rate. Its rate of spread is very fast. Again, it can move in the air. The basic pathogen biology, again, there’s a functional sexual stage. And where there’s a functional sexual stage, that’s where crossing over and genetic recombination occurs. So it’s a source of genetic variability. And that there’s some of that genetic variability certainly has to do with the response of fungicides. And then the fungicide site of action, a multi-site versus single site compounds. The multi-site compounds, the resistance risk is far, far lower. | Slide titled “Factors Affecting Fungicide Resistance” contains a bullet point list of factors, as outlined in the audio. |
| So some of our current fungicide choices, the group 11s, group sevens, group threes, 13, and some of our newer groups, U6, 50, and U13. So the old QOIs or strobilurins, The SDHIs, those are the succinate dehydrogenase inhibitors, demethylation or sterile inhibitors, Quintec, and then some of our newer compounds. | Slide titled “Synthetic (Systemic) Fungicide Choices” contains a list of the current fungicide options with text outlining that these options are of moderate-high resistance risk. |
| And then we have multiple contact fungicide choices, sulfurs, oils, biologicals, carbonates, and zinc salts. Fortunately, these contacts are generally in low resistance risk categories. | Slide titled “Contact Fungicide Choices” contains a list of contact fungicides available for use, with text outlining that these are generally in “M” FRAC groups. |
| So a research program that we started in 2018, funded by the Washington Tree Fruit Commission and Oregon Sweet Cherry Commission, and then the Commission on Pesticide Registration and the Northwest Nursery Improvement Association in 2020, we used this to look at fungicide resistance in Group 11 and Group 3. Actually, the project started investigations on Group 3, and as we dug deeper and deeper, we realized that we had a bigger problem than just the 11s. So that handsome fellow on the bottom right is Prashant Swamy. He worked in the lab as a postdoctoral plant pathologist for several years and did an absolutely wonderful job on this in terms of bioassays and molecular biology studies. But he found in the group 11s, 43% of the isolates that we sampled were resistant. And 28% of the group three isolates were also resistance. Now, one thing I will say right here, we know that the occurrence of this resistance or geographical occurrence is widespread. Every different growing area where we sampled, we found the resistance. What we don’t know is how bad it is in each area, which would be the subject of another study. | Slide titled “Research: Groups 11 and 3 Fungicide Resistance” contains a chart of the percentage of resistant isolates for the group 11 and group 3 fungicides in the study, along with a the photo and name of the postdoctoral scholar on the project. |
| So the situation that we were in, I call this the before slide, and you can see this big long list of available fungicides for cherry mildew. Some of them group 11, some group sevens, group threes, some old ones in there, and also some new ones. One of the new ones is Miravis, which is a group seven. Another is Cevya, a group three. So these are the synthetic choices before. | Slide titled “Synthetic Cherry Fungicides (Before)” contains a chart of the synthetic choices for cherry fungicides, their FRAC groups, and whether they are a pre-mix compound. |
| And now that we know about the resistance to three and 11, this is essentially what we’re left with after. Now, in terms of the group threes that we’ve dropped out of this, we have no idea other than we’ve documented resistance there, but what we don’t understand is the nature of the cross resistance. Supposedly, the Cevya, its a new group three compounds, reportedly has a unique binding process. So we don’t really know how that fits into the group three story. But, as you can see, as we go from before to after, we’ve really limited our choices. | Slide titled “Synthetic Cherry Fungicides (minus Groups 3 & 11) AFTER” shows the same chart of fungicides, but the group 3 and 11 formulations have been removed, leaving only seven options for synthetic fungicides. |
| Fortunately we do have some non group three and 11 options, and some desired outcomes. Keep in mind that the group sevens are also effective against mildew. And I put Luna Privilege up here because Luna Sensations is one of the best tools that we have. And again, it’s a group 11, group seven mix. And with resistance to the group 11s, I’m a little worried about the group 7s. If you still want to use Luna or the Fluopyram, the active group 7 ingredient, if it’s available, you can use Luna Privilege. A new group 7, and again, the Privilege and Miravis and Fontelis are all standalone compounds. A new one is Miravis. It’s a group 7. And keep in mind, that you have to manage resistance to these. These are available, they’re effective against powdery mildew, but you preferably need to tank mix them with another mode of action and always alternate them with a different mode of action. Sulfur is relatively cheap and it’s a very effective fungicide. So it never hurts to throw sulfur in a tank with any of these single site of action compounds. Then some of the newer chemistries, Gatten, Torino, and Vivando. Again, these are good mildew compounds and Quintec is still available. So we still have options. | Slide titled “Fortunately, there are non-3/11 options and desired outcomes” contains a chart of the remaining seven synthetic cherry fungicides. Text to the right highlights that these have a moderate resistance risk. |
| One of the recommendations in other areas they’ve had problems with group three and group 11 fungicide resistance has to do with what’s called a fitness penalty. And what a fitness penalty is, is the frequency of the resistant population will decrease when the selection pressure is removed. So in other words, the fitness penalty, if the selection pressure is removed, it reverses the process of resistance development that I talked about earlier. | Slide titled “2021 Growing Season Steps-Groups 11 and 3 (a)” contains the illustration of resistance developing in a fungicide population from a previous slide, but with an arrow pointing backwards. Above this is text showing the definition of fitness penalty. |
| So in many cropping systems, what they do in situations like this, they will put those groups, sites of action on the side for a year or two. So what we’d like to do going forward here, do not use group three or 11 compounds for the upcoming growing season and next, if at all possible. However, there are going to be situations, whether it be you’re worried about some post-harvest diseases, MRLs, et cetera, et cetera, you might have to use one or both. Use alternate chemistry and also use good resistance management techniques for the synthetic options that remain. What I’m most concerned about right now is not managing mildew, it’s managing mildew and putting our remaining synthetic chemistries at risk for resistance. It’s really what I don’t want to do is burn out some of the newer chemistries we have while we’re trying to revive the older chemistries. So in terms of resistance, do you have it or not? If you aren’t certain, but you’ve had some challenges managing mildew, I would assume that your strain is resistance. | Slide titled “2021 Growing Season Steps-Groups 11 and 3 (b)” contains a bullet point list of reminders for resistance management, as outlined in the audio. |
| Now, some evidence for resistance, rapidly increased difficulty managing mildew in your orchard, a general decline in mildew control over the seasons. This would be a real good indicator that there’s a problem with group threes in there. And importantly, catastrophic control failures in your neighbor’s orchard. Again, the canidia of this fungus can move by wind, so they can easily move from orchard to orchard. And this doesn’t mean that you need to go over and shame your neighbor. What it means is you need to be on the same page vis-a-vis your fungicide approach. | |
| So if you’ve already purchased a group three or 11 compounds, or you have in storage, or you have no other options given the circumstances, use no more than once the entire season. That would be one shot of group three, one shot of group 11. Tank mix with sulfur or some other frack group. Use the higher labeled rate. Know the contents of your fungicide program. This is particularly important with the premixes and if you get a fungicide recommendation that’s only a trade name. You also need to have the common name of the chemical and also the FRAC group number when you look at your season long program risk. Ensure that your fungicide dollars actually reach the tree and the fruit. Again, coverage and calibration is extremely important. Plan ahead. We have options, but there may be MRL and PHI issues with the alternatives. And really get on the same page with your neighbors and colleagues about your local disease or mildew management programs. It’s very important that you know what your neighbors are doing and that you work together and try to attack this problem as an industry. | Slide titled “2021 Growing Season Steps-Groups 11 and 3 (c)” contains a bullet point list of reminders for resistance management, as outlined in the audio. |
| So the 2021 growing seasons, looking at table one, cherry fungicides containing group 11s, you can see Abound, Cabrio, Gem, Luna Sensation, Miravon, Pristine, and Quadrastop. And I put an off-centered box there because some of those premixes in the red box, some of those premixes contain a group seven. And without the active group 11 component in the premix, remember that we no longer have built-in resistance management to the group seven component of that premix. And then some cherry mildew fungicides containing group three compounds, Rally, Procure, Topguard, Cevya, Unicorn, Quadrastop, and some generics. Again, with the Cevya, it reportedly has a unique binding site in the fungus that may make it behave differently than the other Group 3s. So this is something that, if you’re interested, you should look more closely into with the manufacturer. | Slide titled “2021 Growing Season Steps-Groups 11 and 3” contains two tables. The first is of the cherry mildew fungicides containing group 11 compounds, and the second is of the fungicides containing group 3 compounds. A red box is drawn around Luna sensation, Merivon, and Pristine to indicate that they are premixes and contain group 7 compounds. |
| And again, I don’t want to beat this to death, but the important thing about the Group 11 premixes, if you lose one to resistance, in this case, group 11s, it puts more resistance pressure on the remaining compound in the premix. | Slide titled “Group 11/7 Premixes” contains text outlining an example of what to do if you must use a group 11/7 premix. |
| So Luna Privilege, this is registered in Washington state and it’s registered on stone fruit, but I don’t know much about its availability. It was pretty scarce several years ago. So that’s why I said here that it’s elusive. But it is the same thing, fluopyram, as the seven component in Luna Sensation. And it’s effective against mildew and some post-harvest rots. But again, if you’re using this in the tank, be sure you tank mix it with something else that’s effective against mildew, sulfur or some other appropriate mode of action. | Slide titled “Luna Privilege (fluopyram)” contains an image of the pesticide label for Luna Privilege as well as text highlight that it does not have built-in resistance management when used as a solo product. |
| The same thing with Miravis. It’s a group seven, good mildew material, but we have to manage resistance to it. | Slide titled “New Group 7 Compound” contains an image of the pesticide label for Miravis along with a reminder to use a companion product. |
| Now, something that came up a few weeks ago were post-harvest cherry pathogens. And one of the comments that we received was some people felt that these premixes, the 11-7 premixes were also giving the added benefit of improving post-harvest pathogen control. | Slide titled “Postharvest Pathogens” contains a photo of grey mold on stored cherries. |
| And I looked into this a little deeper. And again, you don’t wanna put on a 7-11 premix by itself if the 11 is no longer controlling mildew. But you also have to worry about, in some cases, post-harvest pathogens. So there are other compounds that can either go in the tank or be used post-harvest that can help with post-harvest pathogens. And one of those is fludioxonil, known as either Scholar or FDL or Elevate, phenhexamid. These compounds will also control post-harvest cherry pathogens such as botrytis and brown rot. | Slide titled “Postharvest Pathogens” contains images of the pesticide label for PacRite FDL , Scholar, and Elevate fungicides. |
| And they’re relatively effective. If you look down here, this again comes out of California. Pristine gets three stars on brown rot, gray mold, and Rhizopus, as does the fludioxonil or Scholar. And the phenhexamid gets a three for gray mold and two for brown rot. And again, this particular chart is out of date. It is now registered in the state of Washington. | Slide titled “Efficacy of selected fungicides for control of three postharvest decays of sweet cherry” contains a chart showing the efficacy of several fungicides. An arrow is used to point out that Scholar is effective against brown rot, grey mold, and Rhizopus rot. |
| So in terms of our current lifeline, and I consider our current lifeline the sevens, group sevens and all the new synthetic frack groups we have. We need to approach this as an industry that we’re all on the same page. The university, packing houses, distributors, consultants, and growers. Try to give the groups 3 and 11s a rest to preserve them long-term. Try to take advantage of the fitness penalty. Get the fungicide to the target. And most importantly, while we’re dealing with this situation, be sure to manage the resistance to the newer synthetics, such as the 7s, the 50s, et cetera. The non-synthetics that remain, and again, we could use Fontalis or Miravis or Fluopyram here. Apply no more than twice per season. And you may see this on the label that you can use twice in sequence. My personal recommendation while we’re in this situation, no sequential usage. Always tank mix with another mode of action and always use protectively. | Slide titled “Preservation of Current Lifeline” contains a bullet point list of the steps for preserving the currently available and effective fungicides, as outlined in the audio. |
| And okay, I’ve already said this before. So I’ll go through a little bit that we know about the remaining compounds. Again, Fluopyram, remember to use an effective Group 7 companion product tank mixed with this. There are tolerances to this: US, Mexico, the European Union, Australia, Canada, China, Hong Kong, Japan, Korea, and Taiwan. | Slide titled “Luna Privilege (fluopyram)” contains an image of the pesticide label for Luna Privilege as well as bullet points outlining the need for a companion product, and a list of countries with documented tolerances to this product. |
| Miravis, Group 7, pre-harvest interval of zero, REI of four hours, but importantly, tolerances, US and Mexico, European Union, Australia, Canada, Japan, and Korea. I need to move something here. | Slide titled “Miravis” contains an image of the pesticide label for Miravis as well as bullet points outlining its FRAC group, mode of action, preharvest interval, REI, and the countries with documented tolerances to this product. |
| Gatten or flutianil. A U13 compound. It inhibits haustorium formation. This is a pretty unique mode of action. Pre-harvest interval is three. It’s locally systemic and tolerances in US, Mexico, European Union and the UK, Canada, Japan and Korea. | Slide titled “New Synthetic Chemistries” lists information about Gatten, including its mode of action, preharvest interval, and the countries with known tolerances to this product. |
| Vivando, group 50, this, the mode of action, it disrupts the recognition process between the tree and the fungus, pre-harvest interval seven days, locally systemic, and tolerances U.S., Mexico, EU, UK, Australia, Canada, Japan, Korea, and Taiwan. | Slide titled “Newer Synthetic Chemistries” lists information about Vivando, including its mode of action, preharvest interval, and the countries with known tolerances to this product. |
| Torino, group U6 compound, mode of action unknown, but they, the company that makes this is extremely concerned about resistance to this compound. So they recommend its use infrequently. Comparable efficacy to other fresh synthetics, tolerances: US, Mexico, EU, UK, Australia, Canada, Japan, and Korea. | Slide titled “Newer Synthetic Chemistries” lists information about Torino, including its mode of action, preharvest interval, and the countries with known tolerances to this product. |
| This is what we’re shooting for. I mean, this is the bottom line. | Slide titled “Desired Outcome 1” contains a photo of cherries in a bin which are clean and free of visible fungi. |
| But if we can take advantage of the fitness penalty, we may get back to an even greatly expanded fungicide toolbox for the management of cherry powdery mildew. | Slide titled “Desired Outcome 2 (Kudos to the fitness penalty)” contains the chart of all available synthetic cherry fungicides from a previous slide. |
| Now in terms of MRLs, I used a couple of sources to get some of the basic information here, but I found two really good sources of information and you will need to dig into this deeper. One is some work that Tory Schmidt has been doing over the years. And it’s posted on the Tree Fruit Research Commission website. A lot of information about minimum residues, maximum residues, medium residue, et cetera, et cetera. And it really puts these MRLs into like a real world perspective in terms of what’s happening in our cherry orchards. Extremely valuable. And maybe I skipped over it. Well, the slide was embedded, but I found the export manual in the Northwest Hort Council on the Northwest Hort Council website, extremely informative in putting this together. So I’m not an expert on MRLs and marketing, but a lot of the information is available about this. | Slide titled “Essential MRL Information” contains a chart of minimum, maximum, and median residues vs MRLs of pesticides applied to cherries near Orondo, WA from 2012-2020 and a link to the mentioned study. |
| So in summary, back to the group threes and group 11s, I realized the situation we’re in here and we’re not going to be able to eliminate their use entirely. Some of you may not be in the situation where you have any options at certain times a year. But what I’m getting at here, really, let’s really try to minimize their use for the next couple of years and take the selection pressure off of them. | Slide contains a close-up photo of coral growing on a rock in the ocean. |
Link to YouTube video: Sweet Cherry Powdery Mildew updates by Dr. Grove.
