Is it important to quickly prune out fire blight infected materials soon after an infection occurs? How we remove them effectively? And what about sanitizing or not our tools? Tianna DuPont, Washington State University Extension, discussed fire blight pruning at a Fire Blight Fruit School that took place in Wenatchee on February 23, 2023. This project was funded by a grant by the USDA SCRI.
Text Transcript and Description of Visuals
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| What we’re talking about here is managing our Fire Blight infections, pruning and sanitation. So once you have an infection in the block in the summertime, what it is that we actually want to do. | Title slide. Presentation title: Managing Fire Blight Infections: Pruning, Sanitation. Author information: S. Tianna DuPont, Kerik Cox, Ken Johnson, Kari Peter, Misbakhul Munir, Aina Baro. |
| And the reason that we’re looking at this is, we had a number of bad years of Fire Blight. If you guys remember back to 2017 and 2018, and growers were spending a lot of money, a lot of time cutting Fire Blight out of their blocks. They reported after that 2017 infection, two to 64 hours per acre. Which–gosh it’s hard to think of it–it only costs 13.50 an hour at that point for our labor. But it was getting to be really quite expensive. | Slide titled “Removal of Fire Blight = Costly” contains a photo of an apple branch which shows the characteristic “shepherd’s crook” symptom of Fire Blight infection as well as wilting leaves. To the right, text highlights the high costs for growers treating infections. |
| And so folks were saying, well is there anything we can be doing differently? We know we need to manage these infections, but we didn’t necessarily always feel like we were doing a great job, because we’re going out and spending a lot of time cutting and still seeing new shoot blight infections popping up in that block. Then going, oh God, I have to go back and back again to try and manage this infection. So can I do a better job, and also is there anything we can do to be more efficient so that it’s maybe not quite as expensive? | The limb of a tree appears over a white background. Wilting of leaves is seen near the tip of the branch, and bright flagging tape has been used to mark the symptomatic leaves. Pruning shears are positioned to cut the limb at around 18 inches from this flagging tape. |
| So you all know our standard practice is cutting 12 to 18 inches back from that infected area. If your infection is here, trying to get where that bacteria is moving through the tree ahead of the bacteria, so that it doesn’t continue moving through the tree to create systemic infections and rootstock blight. But should we be more aggressive? Less aggressive? Do we need to sanitize our shears? Do we not need to sanitize our shears? At that point in time, we were getting a lot of questions. So we looked back through the literature and realized, wow, we’ve got standard recommendations but actually not as much data as you might think because everybody thinks this is just a really basic thing and we already know the answer. | A pointer is used to highlight the leaf wilting symptom, and then the position where the pruning shears are primed to cut. |
| So we decided to actually do some trials looking at this. So we did 10 trials in Washington, Pennsylvania, New York, and Oregon comparing six different treatments: that best management practice of cutting 12 to 18 inches back from the noticeable infection, an aggressive cutting of 30 inches back from that noticeable infected area, a breaking treatment that I’ll talk about that some growers were trying in their orchards, as well as leaving a long stub, a short stub, and sanitizing or not sanitizing. | Slide contains six labeled photographs representing the six different treatments used in the trial: Best Management Practice, Aggressive, Breaking, No disinfecting, Long Stub, and Short Stub. |
| So to go through that not quite so fast, remember our best management practice was just the standard. It was cutting back 12 to 18 inches into two-year-old or older wood with sanitized shears. So sanitized with Clorox or Lysol or oxidate or so forth. | Slide titled “Best Management Practice” shows an image of a marked, symptomatic branch being cut with pruning shears at around 18 inches from the wilted leaves. Text above outlines the procedure. |
| But we thought, well maybe if we’re more aggressive, we are getting further ahead of that infection. Maybe in younger trees, more vigorous trees, we’re going to do a better job. So we thought, well if we’re cutting back two and a half feet from that noticeable infection we’ll have better control. Oftentimes this was cutting down into the central leader in our more high density systems and stumping the tree | Slide titled “Aggressive” contains images of a marked, symptomatic limb being cut with pruning shears down to the central leader of the tree, and the small stump that is left behind after that limb is removed. |
| We also looked at breaking, which was breaking back those shoots manually by hand. So avoiding using loppers, just breaking back between the first year and the second year old wood. | Slide titled “Breaking” contains images of a shoot on an apple tree, and the broken wood that is left after it is snapped off. |
| And we looked at leaving a long stub. So the idea here is that you’re leaving four or five inches between where your cut and the structural wood of the tree. So that’s the central leader or another large leader of the tree. And you might not always be that full 12 to 18 inches back, but hopefully keeping the infections from the structural wood. | Slide titled “Long Stub” contains photos of symptomatic branches being cut with pruning shears and photos of the four to five inch stumps that are left behind on the structural wood. |
| And then comparing that to when you’re cutting pretty close to the central leader, either with a short stub or a flush cut. | Slide titled “Short stub/flush” contains photos of symptomatic limbs being cut off very close or flush with the central leader, leaving almost no stump. |
| Then, of course, this is all compared to a no treatment control where we either didn’t do anything at all in the research orchards, or we just cut right at the edge of the noticeable infection in the grower orchards where they didn’t want to let it go completely rampant in the orchard. | Slide titled “No-treatment control” contains photos of symptomatic branches, which have been marked with flagging tape. |
| One thing that’s important about this project is we did this in a number of different types of orchards. So different varieties, different rootstocks, different vigor, because, of course, the way that we prune and cut is going to affect these trees differently depending on their vigor and age. So, for example, in New York most of the trials were done in quite young, quite vigorous trees. In Oregon, they were also three-year-old Galas on M9.337, and in Pennsylvania they were also young Galas on M9 and M7. | Slide titled “Trials in different vigor, variety, age.” contains photos of the different orchards and text information about the different rootstocks, varieties, and ages used. |
| In Washington the first trial we did, these were natural infections. So where we had a block with a lot of Fire Blight that they let us work. They were ‘Yarlington Mills’, so a cider apple variety, on Red Delicious inner stem graft. So quite vigorous grafts, but the older inner stems and rootstocks. | Slide titled “WA 2019 ‘Yarlington Mill’ on Red Delicious interstem grafts” contains a photo of the orchard block used for the trial. The wilted leaves and shepherd’s crook symptoms are visible on several of the trees. |
| The 2020 experiment was done in ‘Pink Ladies’. These were older trees that the orchardist considered to be relatively low vigor. They don’t put huge amounts of nitrogen on these trees, and they’re a little bit older, 14 year old block. | Slide titled “WA 2020 ‘Pink Lady’ 14-yr-old on M9.337 low vigor” contains two photos of trees showing leaf browning and wilting symptoms. |
| And the 2021 trial was done in four-year-old trees that were on a V-trellis that was trained to the wire in this system and relatively young trees | Slide titled “WA 2021 ‘Pink Lady’ 4-yr-old on M9.337 trained to wire” shows a photo of the trellised orchard used in the trial. |
| So the first question we were asking, kind of one of the most important questions is: what can we do that’s actually going to save these trees, right? So when we have Fire Blight infections and that bacteria moves through the tree, it can get down to the rootstock. You can see that here, where the tissue, the cambium is dead and will eventually be oozing. Then you can get death of those trees, which then have to be removed. And so we want to try and keep this from happening. | Slide titled “Which removal treatments save trees?” contain three photos of systemic fire blight infection. A pointer is used to indicate the cambium at the base of the trees, which is darkened and degraded. |
| So one of the things that was quite striking about these experiments is that in six of the ten experiments, we did have either rootstock blight or root death. And in four of those, the ones in New York, all of the trees that had no cutting–they didn’t go in and do any summer cutting–died. All of them, 100 percent. All of the trees that received some type of pruning of those summer Fire Blight infections didn’t die. | Slide titled “Cutting treatments significantly reduced the number of trees which died or acquired rootstock blight” contains bar graphs for two different trials in New York in 2019. Each graph shows the percentage of tree death for each of the six tested treatments. |
| So this is below zero just because otherwise you’d have a lot of blank on your graph here. So 100 percent tree death on the no treatment control, NTC, and all of the cutting treatments save those trees. So this is just a reminder when you guys say, do I really need to cut it out now? Can I just wait for the winter? Well at least on young vigorous trees, you really are risking the life of those trees if we’re not going in and cutting out that blight. | A pointer is used to highlight the treatments other than the no-treatment control, which appear as below zero on the graph. |
| In the Washington 2021 ‘Pink Lady’ trial, this wasn’t quite as dramatic, but we did have 38 percent rootstock blight in the no treatment control compared to zero to sixteen percent. There’s a funny little blip in one of those treatments, in the cutting treatments. | Slide contains a bar graph of the percentage of rootstock blight for the six treatments used in the trial, as well as a photo of cambium death in the rootstock. |
| So the next question we were asking is: how can we prevent systemic infections? Remember that fire blight bacteria is moving through the tree much faster than the symptoms that we actually see. And it’s going to congregate in that young tender tissue, and you’ll see these secondary infections or systemic infections where that bacteria has moved from the initial flower infection. | Slide titled “Prevention of Systemic Infections” contains a photo of the distinctive shepherd’s crook symptom of Fire Blight infection on the tip of a branch. |
| Remember that the we can see that a little bit when we just scrape back the bark and look at the cambium of the tree. You can see you know this cambium is all dead away from the canker, which is down here. So you can see that, oh yeah, that that was affecting more than just what I could see with the canker. | Slide containing a photo of a fire blight infected branch. The bark has been scraped away to reveal cambium tissue that is brown and dead. |
| But that bacteria is actually moving through the intercellular spaces of the plant much faster even than that death that we can see. So remember, Aina was talking about earlier in the day how those bacteria are moving through the intercellular spaces of the plant. | Slide containing a diagram illustrating the bacteria spreading through the intracellular spaces between the plant cells. |
| Then they’re getting into the vascular system, so the plant xylem, and moving through the tree. | Slide contains two illustrations of bacteria moving into and colonizing the plant xylem. To the right are microscopy images of the bacteria within the plant xylem. |
| So as we’re trying to cut out blight, if we have an infection here, we know that bacteria is moving through the tree. So we’re trying to cut ahead of where that bacteria might be so hopefully there aren’t very many bacterial cells still left in the tree to create a new infection. | An image appears of a person cutting away a symptomatic branch with pruning shears. Arrows are drawn on screen indicating the site of the infection, and the direction that the bacteria is moving, back towards the rest of the tree. |
| So overall, the best management practice, shown in yellow here, did reduce those systemic infections in seven of the nine experiments. It reduced them significantly in five of the nine, compared to the no treatment control. | Slide shows a bar graph of the new infections per tree for the six tested treatments in the Washington 2021 trial. The best management practice treatment is highlighted with a red box. Text to the right outlines the results of this trial. |
| There were a couple of exceptions. One of those was in those 14 year old pink lady trees in Washington that were relatively low vigor. You can see here in the right hand side, they just really didn’t have very many new infections. So when I’m saying new infections, that’s when we went in and cut and then we came back and looked to see if we had any more infections that occurred after our initial cutting that we think might have been from those systemic infections. | Slide titled “BMP generally reduced the number of new infections” contains eight bar graphs of the new infections per tree for the six tested treatments. Each of the trials is represented by a bar graph. A black arrow points to the results of the 2020 Washington ‘Pink Lady’ trial. The new infection rates are very low for all of the treatments. |
| The other exception was a block in Pennsylvania where they’d had a very cold spring followed by a very hot summer immediately. And so they had a terminal stopping of terminal growth pretty quickly. And so they also didn’t get any more new infections in that block. So we do have a lot of variability here, but in general, that best management practice reduced the number of new infections that occurred. | |
| So we do have a lot of variability here, but in general, that best management practice reduced the number of new infections that occurred after we did our initial cutting. So think about it, if you sent your crew through the block, you think they got every infection that they saw at that point. Which, of course, we missed some, right? But then when you would go back that second time with your crew, how many more you might find. Well we were hoping though, that by cutting more aggressively, right? So two and a half feet from that infection versus just a foot, we’d be able to reduce the number of those systemic infections or the infections that occurred later. | Slide titled “Can aggressive removal reduce systemic infections?” contains photos of pruning being done to symptomatic branches. |
| So when we compare the yellow bars here to the pink bars…So this is number of new infections per tree after we went through and cut in these blocks. And remember, this was when we were looking very carefully at each tree so I’m hopefully doing a pretty thorough job. Interestingly, in general if you look at the letters here, the aggressive treatment was not better than that best management practice. The one exception was these 2019 ‘Yarlington Mills’ which remember were those grafts. | Slide titled “Treatment Aggressive had fewer new infections than BMP at “Washington 2019 ‘Yarlington Mill’ but the number of new infections was not significantly different than BMP at other sites” contains seven bar graphs of new infections per tree for the control, BMP, and Aggressive treatments. |
| And one thing though to note is, unfortunately with this aggressive treatment, we’re oftentimes stumping these trees. And so the reason we weren’t seeing a lot of additional infections, in some cases, in these blocks was there was just no tissue to get infected, right? So this is actually a picture from the 2020 block, but if we cut down too far we’re not going to have enough buds to get regrowth or need to re-graft in those blocks. So overall it seemed that the best management practice is actually doing a pretty good job and being more aggressive might not be necessary in these cases. | Slide shows two photos of trees in which the limbs have been cut off, leaving only stumps. |
| Also in the 2021 block we got a lot of vigorous regrowth from that real aggressive treatment, which is young tender tissue that could be then really susceptible to Fire Blight. | Slide show two photos of trees with heavy browning and wilting of leaves. |
| So the third question that I was interested in, is can we do a stub cut to keep from getting cankers on the structural wood? So what I was seeing at that point was blocks with trees like this. You’ve got a canker on the main trunk of the tree, and guys are going “Do I really need to cut that out? What percentage of those are really going to ooze in the spring? I those are dead. See they’re dried up, Tianna. They’re dead, right? I don’t need to cut those out.” And we’re going “Well it might only be 10 percent of those that ooze in the spring, but that’s still inoculum for your block. I don’t know how you’re going to guess which ones are the 10 percent that are going to ooze, right?” So if we can keep from getting cankers on the central leader of the tree or a big leader of the tree that you guys don’t want to cut out, hopefully that that would help reduce the amount of inoculum that you’re dealing with year after year. | Slide titled “Can a stub cut keep cankers from reaching structural wood?” contains photos of stem cankers on the trunks of two trees. |
| So there’s this idea out there, it’s not new it’s been talked about since the 80s, of doing a stub cut or an ugly cut where you’re leaving this four to five inch stub. Then you can come back in the winter time and remove if you do get reignition where there’s still enough Fire Blight bacteria left that you get a small canker. But that canker won’t be on a structural wood here, where you guys don’t want to cut it out and it ends up getting left in the block. | Slide show several photos of stubs left on trees after a branch has been cut. A blue line is drawn on one of the photos to indicate where a secondary cut would be made in the winter. A Red line on another photo indicates where the canker would appear on the structural wood. |
| To kind of explain that a little better, if this is your infection here. If you’re cutting too flush to the tree, if you get re-ignition or enough bacteria that you have another canker form and it’s on that structural wood, you’re going to have to then come back in and stump that tree, versus if you leaving this four to five inch stub. If you get a little bit of a small canker in the winter, hopefully you can come back and cut that out and your main leader is going to be clean. | Two diagram show outcomes of cuts made to the tree. The top diagram shows a branch being cut flush with the tree and a canker forming on the trunk. The bottom diagram shows a stub being left, forming a canker, and being removed from the trunk. |
| And so with this, sometimes you’re not cutting the full 12 to 18 inches back from this infection. In this case, you can see it’s maybe 10 inches. We’re skimping a little bit to try and leave that stub and see if we end up with a better job. | Slide shows images of a short stub cut and a long stub cut being made on the tree. The long stub cut is being made less than a foot from the site of infection. |
| So this was a little bit variable. We only, in five of the trials did we test this actual treatment. In two of the five trials, we did see a reduction in the cankers on the structural wood. So the long stub here is this turquoise bar, compared to the blue bar, the short stub in this block, where we were able to keep cankers from being on the structural wood. However this didn’t happen all the time. But remember, some of the exceptions were, for example, the Pennsylvania 2019 trial, where they had no new cankers or infections because of the environmental conditions in that block. And the Washington 2019 trial which was the grafts on ‘Red Delicious’ where it’s unlikely that you’d be seeing that on those ‘Red Delicious’ inner stems. | Slide contains a bar graph of the percentage of strikes progressing to structural wood for each of the six tested treatments in the Washington 2020 ‘Pink Lady’ trial. The long stub and short stub treatments are highlighted and show 0% and 13% strikes respectively. |
| So the fourth question was: what about breaking? Folks were trying this out, particularly down in the Tri-Cities area. That happened to be the growers that were showing this to me, where they were going through breaking back at the joint between the first year and the older wood. | Slide titled “Breaking?” shows an image of a hand reaching up to break an infected stem off of a tree. |
| This was particularly the case when you’ve got trees that are trained to a wire. So I had been lecturing folks until I had to go through and actually try this and realized how difficult it is to cut back 12 to 18 inches when those branches are tied to the wire, because you have to cut them off the wire and then cut the branch and it was taking forever. So I’m not… it seems like a really good idea to be able to come through and just break this off. You’re not then having to use shears that you have to sanitize. It was very fast. So the question was, is this a good idea? | Slide titled “Breaking” shows a photo of a V-trellised orchard and three photos of hands grasping and breaking the first year growth off of the tree. |
| You can kind of see a little bit better here, the breaking or trying to mimic what the crews were doing in that block. | An image appears of a hand grasping on of the first year growth branches in order to break it off the tree. |
| Well unfortunately we found a couple of things. In some cases, so particularly this block of ‘Pink Ladies’, where the branches were trained to the wire. Where we did the breaking, this red bar here, we had a significantly higher number of new infections. This was really similar to the no treatment control. So systemic infections are popping up throughout that tree, probably because we’re not going back very far from where that infection occurred. And so there’s still a lot of bacteria left in the tree to move around in the tree. | Slide titled “In experiment ‘Washington 2021 Pink Lady’ where 4th leaf trees were trained to the wire, treatment Breaking resulted in significantly more new infections than other cutting treatments.” contains a bar graph of the number of new infections after initial cutting for each of the six tested treatments. A photo to the right shows an apple tree with 11 red circles indicating the new infection sites. |
| The other thing we saw was more cankers left in the tree at the end of the year in three of the trials. So this would be more sources of infection for the following years. So you see the red bar bigger than most of the other cutting treatments here. | Slide titled “In three of the ten experiments Breaking resulted in significantly more canker tissue left in the tree at the end of the season compared to BMP” contains three bar graphs of the average length of cankers in tree at the end of the season for each of the six tested treatments. This data is shown for Washington 2019, Oregon 2020, and New York 2021. The breaking shows higher than average canker length in each of these trials. |
| And in one of the trials, we also saw more of those cankers on the structural wood where it’s going to be harder to remove them. We also saw trend where, in five of nine of the trials, while it wasn’t significant, you had a larger numerical number, for whatever that’s worth, on the structural wood. | Slide titled “Breaking = higher numbers of cankers on structural wood than BMP” contains a bar graph of the number of strikes progressing to structural wood for each of the six tested treatments in the Washington 2021 trial. The breaking treatment shows a higher number of cankers than all treatments, including the control. To the right is an image of a canker on the structural wood next to a break. |
| So that breaking treatment seems to be leaving a lot of cankers in in the orchard and on the structural wood. It might be really fast, but there’s definitely some trade-offs there and something that I’m concerned about. | Slide contains two images of cankers on the structural wood of trees, and text highlighting that breaking can lead to more cankers. |
| The last question that we always are scared to answer, but I’m gonna do it today, is give you our data on if we should we sanitize our shears. So for years, we plant pathologists, we’ve always said you need to use a 10 percent Clorox or ethanol or Lysol to kill the bacteria on your pruning shears so that you’re not moving it around the orchard, because of course we don’t want to be moving bacteria from tree to tree. But, what have we been talking a lot about today about how bacteria moves through the tree? Yeah, intercellular, way ahead of what we are actually seeing. So that means that a lot of these strikes that we’re seeing later on are probably from bacteria that was moving through the tree, not from bacteria we could be moving around with our shears. And so that’s really changed the way we might start thinking about this question of sanitizing our shears. | Transition slide titled “Importance of sanitizing out tools?” contains a photo of the shepherd’s crook symptom of fire blight infection. |
| So what did we find? Well in all of the trials, we didn’t get any more new infections, what we would think are systemic infections, from the no sanitize treatment. So that same cutting 12 to 18 inches back, but without sanitizing our shears compared to with sanitizing our shears. One thing to keep in mind is, this is in a relatively controlled situation, you know? We were out in orchards, doing these cuts, but we’re very carefully doing the cuts. And to my knowledge, and I was out doing a good portion of the cuts, we never were cutting through active ooze, so actual goo that we’d be moving to another tree. So there’s going to be a little bit more potential when you’re doing thousands and thousands of cuts than what we saw. But again remember, when you’re cutting, you’re not cutting into that young tender susceptible tissue. We’re cutting into older wood, so we were not seeing a benefit of sanitizing our shears. | Slide titled “Sanitizing tools” contains eight bar graphs of the number of new infection after cutting for the regular BMP and the BMP with no sanitization treatment. For each of the shown trials, very little difference was seen between these treatments. |
| So overall most important, timely summer cutting can reduce rootstock blight and tree death. So let’s make sure to do that whenever possible, especially in young vigorous trees. That standard of cutting 12 to 18 inches back from the infected area into two-year-old or older wood did seem to do a good job of reducing systemic infections, and the aggressive cutting didn’t necessarily seem to be any better. That breaking treatment seemed to leave a good number of cankers in the orchard, and leaving that stub, at least in some cases, was reducing the a number of cankers on structural wood. | Conclusion slide lists important reminders for fire blight protection, as outlined in the audio. |
| So with that, thank you to all the folks that are part of the SCRI project, and to my partners on this particular objective of the project. I’m happy to take a couple of questions if there’s any at this time. | Thank you slide showing pictures and locations on a map of all of the project participants as well as logos of funding sources for the project. |
Link to YouTube video: Managing Fire Blight Infections: Pruning, Sanitation – YouTube
