General tree removal recommendations and new trial results presented by Cody Molnar, WSU ITT Extension and Tianna DuPont, WSU Extension. Cherry Institute 2021. Sponsored by NW Cherry Growers and WSU Extension. Videography and production Nick Dirk.
Text Transcript and Description of Visuals
| Audio | Visual |
|---|---|
| Okay, good morning everybody. My name is Tianna DuPont with WSU Extension. I’m going to present this presentation on behalf of myself, Cody Molnar, and Ricardo Naranjo with WSU Extension, as well as Garrett Bishop with GS Long. We’re going to talk a little bit about tree removal for X disease and little cherry virus. | The speaker appears against a white background. Text on screen reads “Tianna DuPont, WSU Tree Fruit Extension”. |
| So the reason why we’re talking about this is it’s really important that we remove trees that are infected with X-disease or Little Cherry Disease. That’s because these trees, the infection is throughout the tree. We might think, like this tree here, that we only have an infection in one branch. You can see the picture on the left is that one very infected branch with the light colored fruit. However, that infection is throughout the tree, and so if we just remove one branch, we’re still going to have a source for the infection to move throughout that orchard as the insects feed on those trees. | Slide containing two photos of infection in a cherry tree. The first is of the whole tree, on which there are many healthy branches and fruit clusters and one branch with small, discolored cherries. The second photo is a close-up of that symptomatic branch. |
| Two important things to remember with X disease and Little Cherry Disease is that, not only are they spread by grafting, they’re also spread by insect vectors. And that grafting is not only propagation, but also root grafting. So we can have movement from tree to tree down the orchard row when those tree roots grow together and are root grafted. | Slide comparing X-disease phytoplasma and Little Cherry virus-2. Bullet point lists detail that X-disease is a phytoplasma affecting Prunus species, spread by grafting and leafhoppers and that Little Cherry Virus is a virus affecting cherries and other stone fruits that is spread by grafting and mealybugs. A photo to the right shows cherries which are lightly colored, small, and misshapen. |
| So our general recommendations for tree removal have been to first scout and mark those suspect trees. And then if you have already documented X-disease or Little Cherry Disease in the orchard, go ahead and just take out those trees as long as the symptoms are obvious and you feel comfortable that indeed that’s what the problem is in the block. If you haven’t documented these pathogens in the block or in the area, then please sample those trees, send them into the lab, and document whether they’re positive or not for X-disease or Little Cherry, and then remove those positive trees. When you’re doing your tree removal, there’s a couple things to keep in mind. First of all, you want to spray your insect vectors before you remove the trees. That’s in order to make sure that the insects that then might be feeding on those trees don’t just move to adjoining trees in the block. | Slide titled “General tree removal recommendations”. On the left is a bullet point list outlining steps for scouting, sampling, and removing infected trees. On the right are photos showing a tree stump being treated after cutting and an herbicide injection into a tree trunk. |
| And then we suggest that you either use a glyphosate herbicide application when you remove the tree or test adjoining trees in order to see if you have non-symptomatic adjoining trees. Then you’re going to remove those adjacent trees with herbicide injury or with positive results. And if more than 20% of the block is infected, you probably want to consider removing the whole block. | |
| So to explain this a little bit better, this is an example where you can see where a tree has been removed and you can see that the two adjoining trees have herbicide injury from when they applied glyphosate to that stump. Those two trees that look dead and brown were probably root grafted to that tree that was removed. That means that if they were root grafted, the pathogen had already moved to those trees even though they weren’t symptomatic and they need to be removed. So the herbicide is giving you an early warning so you can get ahead of this pathogen movement in the block. The herbicide is also killing those roots so that you have fewer living roots that adjoining trees could grow into, root graft, and become infected. | Slide containing a photo of an orchard row. In the center there is the stump of a tree labelled “Infected tree removed”. On either side of the stump are trees which have brown, droopy leaves from herbicide damage labelled “Root grated, likely infected. Remove”. Next to one of the herbicide damaged tree is a healthy looking tree labelled “Test”. |
| For example, here you can see we have a block where they did that herbicide treatment when they did their tree removal, and you have dead brown trees on one side of those removed trees. Those were trees that were infected with the pathogen, but they weren’t symptomatic. And so by using this herbicide treatment, they were able to detect that early, get rid of those trees, and hopefully slow the spread of the pathogen. | Slide containing an aerial view photo of an orchard in which tree stumps and the herbicide injury of the adjoining, root grafted trees can be seen. |
| But there’s been a lot of questions about this tree removal process. What herbicide rates to use, what application method to use, what time of the year is best, and whether we really need to use this herbicide application because it’s expensive and time consuming and sometimes delaying the tree removal in the block. | Transition slide containing an image of tree stumps in an orchard along with the text “BMPs for Tree Removal?” |
| So we started doing trials in 2019 and continued last year. This first trial was done in Wapato in collaboration with Garrett Bishop from GS Long as well as Ricardo from the Tree Fruit Research Commission. He’s an intern there. These were ‘Bing’ on ‘Gisela 12’ and we did six different treatments in this block. We were comparing a grower standard, which was just applying the glyphosate to that cut stump, concentrating on the cambium area and going across that whole cut stump, and comparing that to two dilute applications. So a 50-50 of water to glyphosate that was applied either with or without an ammonium and surfactant product in order to help uptake of that glyphosate into the tree. | Slide titled “Wapato Site” contains a chart of the six different herbicide treatments in the block as outlined in the audio. To the right, supporting photos show three different application methods for herbicide application, spraying, brushing, and injecting. |
| In this first site, we saw very little glyphosate injury to adjoining trees. You can see just these two branches with a little bit of interveinal chlorosis. That was all of the herbicide injury we got from all of our treatments, which was a little bit sad. We thought, oh my goodness, nothing worked. But that could be for two reasons. One, these were ‘Gisela’ rootstocks, so a smaller rootstock. Or it could be also that there was less irrigation in this block after the harvest, which could have reduced the amount of mobility into those root systems. | Slide titled “Wapato Site” contains a chart of the percent of adjoining trees with herbicide injury at four weeks. No injury is shown. To the right, two photos show chlorosis of the leaves of two branches involved in the trial. |
| We looked at root death from our treatments by measuring root death from 10 small roots, so less than 10 millimeter, and five large roots from 10 to 30 millimeter. And in this block, we looked at them the following spring. The best treatment was that frill-dilute application where we were applying five milliliters to four cuts that were notched in those trees. But we still didn’t have really great root death. It was around 30% in that best treatment. | Slide titled “Wapato Site” contains a bar graph of the percentage of root death for the six tested treatments. The Frill-dilute treatment has the highest percentage of root death at around 30 percent. |
| You can see here when you look at the roots from that frill dilute treatment that we have death of the cambium, that layer right underneath the bark, sort of browny-orange color in some of the roots, but not all of them. And there’s quite a bit of variability from tree to tree and treatment to treatment in this site. | Photos compare cross sections of roots from each treatment to the control. In the frill-dilute treatment, darkening and degradation of the cambium is seen in some photos. |
| At Brays Landing, we were most interested in that frill-dilute application, which, remember, was done by notching the tree and applying a dilute application. So we tried that again. The grower wanted to see, does it matter if it’s dilute or not? So we looked at that dilute application compared to a concentrate application, drilling holes in the tree every four inches around the circumference of the tree, and either adding four milliliters of dilute or two milliliters of concentrate to every hole. So we ended up adding about a half an ounce of AI to each tree if they were calibrated to a 30 inch circumference tree. | Slide titled “Brays Landing Site” contains a chart of the two different herbicide treatments used, as outlined in the audio. To the right are two photos of holes being drilled into trees and herbicide being injected into those holes. |
| At this site, we saw relatively low amount of herbicide injury as well. We had three adjacent trees out of 53 that had moderate herbicide injury, and those were all in the dilute application. But this was just yellowing. We had no death or severe herbicide injury in adjoining trees. | Slide titled “Brays Landing Site” contains a chart of the percent of adjoining trees with herbicide injury at four weeks. The results show that the frill-dilute caused damage to 3 of the adjoining trees with 40-69% of each of those trees showing damage. |
| At this site, the trees were stumped four weeks after application, and then we looked at the root systems this fall, so five months after application. You can see that we had 97% to 100% root death at this site in both the frill dilute and the frill concentrate application. | Slide titled “Brays Landing Site – Evaluation” contains a bar graph of the percent of root death for the two different treatments. The Frill-concentrate treatment shows 100% root death, and the Frill-dilute treatment shows 97% root death. |
| You can see that nice root death in these roots that we evaluated. See the orange to brown of that cambium layer right underneath the bark, indicating that those roots were dead and were going to continue to completely die over time. | Photos compare cross sections of roots from each treatment. In both treatments, significant darkening and degradation of the cambium is seen. |
| The third site was down in Zillah. These applications were done in August. These were ‘Santina’ on ‘Gisela’. And here we were comparing the cut stump treatment to a Frill-dilute application. The cut stump treatment was done by adding 20 milliliters of glyphosate painted on to the surface of that stump immediately after cutting. And then the Frill-dilute application was holes drilled every three inches around the circumference of that tree, a three-eighths inch drill bit, and adding four milliliters of glyphosate per hole, ending up with a total of one ounce per tree in the Frill-dilute of AI, and two ounces in the cut stump treatment, if we were to calibrate that to a 30-inch tree. | Slide titled “Zillah Site” contains a chart of the two different treatments and the control used in the trial, as outlined in the audio. Photos to the right show trees and stumps marked with flagging tape for the trial. |
| At this site, we also saw very little, actually no herbicide injury of adjoining trees. This could be because these were ‘Gisela 12’, and this is a trend we’re seeing where these smaller root stocks seem to have less root grafting and perhaps less potential then for both the virus or phytoplasma or the glyphosate to move to those adjoining trees. | Slide titled “Zillah Site” contains photos of the trees adjacent to the cut stump at four weeks post treatment. None of the trees show obvious herbicide injury |
| We rated root death at this site at four and eight weeks. This graph is from four weeks where the frill dilute application did a little bit better than the 100% application rate. We had about 48% root death at four weeks and that went up to 56% in the frill dilute application by that eight week mark. | Slide titled “Zillah Site” contains a bar graph of the percentage of root death for the two treatments and the control at 4 weeks post treatment. The Frill-dilute treatment shows the highest percentage at 48 percent, with the cut stump treatment showing around 30 percent root death. |
| We had about 48% root death at four weeks and that went up to 56% in the frill dilute application by that eight week mark. | Photos compare cut sections of roots for the two treatments and the control. Darkening of the cambium is seen in both of the treatments. |
| The last site was down in Quincy. We wanted to do an application in September, which is obviously the easiest time for you guys to be doing these applications after harvest, and see if we’d still be effective that late in the year. So at this site, we just compared two treatments to a no treatment control, the cut stump treatment to the Frill-dilute application, Here we held the amount of AI steady at about one ounce per 30-inch tree for both of those treatments. | Slide titled “Quincy Site” contains a chart of the two treatments and the control used in the trial, as outlined in the audio. Photos to the right show the glyphosate being brushed onto a stump and Frill-concentrate being injected into a trunk. |
| At this site, we had some herbicide injury to adjoining trees. Now, these were ‘Mazzard’, ‘Skeena’ on ‘Mazzard’, so a larger rootstock, more prone to root grafting. We had two adjoining trees in the cut stump and one in the frill treatment that showed quite severe, so death of those adjoining trees from that herbicide. | Slide titled “Quincy Site” contains a chart of the percentage of adjoining trees with herbicide injury at 4 weeks. The cut stump treatment had 7% of trees with moderate injury and 7% of trees with severe injury, and the Frill-concentrate showed 4% of trees with severe injury. The control treatment showed 4% of trees with moderate injury. |
| We also had some problems in some of the control trees which were likely due to Pseudomonas from previous infections. | Slide titled “Quincy Site” contains a bar graph of the percentage of root death for the two treatments and the control at 8 weeks post treatment. The Frill-dilute shows the highest percentage at around 20%, with the cut stump being very similar to the control. |
| But when we look at root death at this site, both at four and eight weeks, we had really quite low root death, about 20% in the best treatment. So at least at a fall evaluation period, we were not getting very good herbicide transfer to those root systems at that timing. And you can see these roots look really quite healthy still in most of the trees and roots at this site. | Photos compare cross sections of roots from each treatments. Very little damage is seen to the cambium, with the highest degree seen in the Frill-concentrate treatment. |
| So how does this change our application methods and recommendations for tree removal? Well, the main thing is still to get rid of those symptomatic and diseased trees. Those are the source of the pathogen. We want to get them out of there as quickly as possible. So make sure to be scouting and marking those trees. However, in addition to treating those vectors before tree removal, when you’re thinking about your glyphosate applications, here’s a couple of things to keep in mind. | Slide titled “General tree removal recommendations” reappears. On the left is a bullet point list outlining steps for scouting, sampling, and removing infected trees. The bullet point “Remove symptomatic/positive trees” is in larger text to highlight it’s importance. |
| One is timing. So both the May and August timing seem to do quite well for root death. The other is method. That frill application method, either by notching or drilling, did seem to do better across all of the trials and statistically better in most of them. The other is rate. So we probably started out with too low of a rate in some of the sites and so making sure we have more than an ounce per 30 inch tree is probably going to be where we want to go and we’ll have to do some rate trials to really figure that out. The other thing is rootstock. So this seems to be most important on ‘Mazzard’ or large rootstocks where you have more potential for root grafting and more likelihood that the pathogen has moved to adjoining trees and that the glyphosate is gonna show you that those trees need to be removed. | Slide titled “New” contains a list of reminders for glyphosate applications as outlined in the audio. On the right are photos showing a tree stump being treated after cutting and an herbicide injection into a tree trunk. |
| So with that, thank you very much and thank you to our funders, the Tree Fruit Research Commission and the WSU Tree Fruit Endowment. And please make sure to check out our resources at treefruit.wsu.edu as well as our recorded presentations. Thanks and have a good day. | Thank you slide containing links to additional information and logos of funding sources. |
Link to YouTube video: Tree Removal for X-disease and Little Cherry Disease
