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| Hello everyone, my name is Adrian Marshall. I’m a postdoc at the Washington State Tree Fruit Research Extension Center and today I’d like to talk to you about some of the research that Dr. Beers and I have done on netting for the control of codling moth. | Title slide. Presentation title: The Effects of Netting on Codling Moth and the Apple Arthropod Community. Presenter information: Adrian Marshall, Post-Doc, Tree Fruit Research an Extension Center, Wenatchee. |
| Netting for apple management is not a new concept. Some of the first use of netting was actually to protect apples from hail damage as seen here in the upper right. Areas in Italy and France had frequent hail events and growers could lose their entire crops if they weren’t protected. | Slide titled “History of Nets in Orchards” contains images of hail-damaged fruit, sunburned fruit, and an orchard with netting covering the trees. |
| While we don’t have as many hail events, we do have another environmental disorder, which is that we get too much sunlight here in Washington state. And like me, when fruit is overexposed to sunlight, it gets a little sunburned. And so growers here have adapted netting for shade to help reduce heat stress to the trees and the sunburn damage. | |
| Currently, sunburn is one of the leading causes of culled apples in Washington state. It occurs when the fruit skin reaches a temperature of 115 degrees Fahrenheit, which in an orchard canopy can happen at an ambient air temperature of just 86 degrees Fahrenheit, and we frequently get that in eastern Washington. To counteract sunburn, orchardists have a few options, which include evaporative cooling through a water mist in the orchard, kaolin clay sprays, which serve as a sunscreen on the fruit, and shade netting. | Slide titled “Fruit Disorder” contains images of various severity levels of sunburn on apples as well as a bullet point list outlining the causes and control methods of sunburn, as outlined in the audio. |
| There are three basic structures for netting over orchards. In the upper left, we have the top cover only, which was one of the original designs. It uses a combination of trellis poles and wires to support the netting just above the canopy, and this provides protection from sunburn and hail damage. | Slide titled “Types of Net Structures” contains images of top cover only, full block enclosure, and tree wrap netting in orchards. |
| In Europe, they adapted the netting to have a tree wrap or row cover, which looks like this on the right, and this uses the canopy of the tree to support the netting. They’ve shown that it provides additional protection from insects like codling moth and birds, but it must be removed to do any pruning, fruit thinning, or at harvest. Here in the bottom left, we have the full block enclosure, which is more commonly found in Washington state. It uses the trellis poles and wires again, but to support the netting above and outside of the orchard to allow machines and crews to access it so it doesn’t need to be removed during harvest. | |
| The use of these drive-in net enclosures is rapidly expanding across eastern Washington. Already established blocks can be retrofitted to incorporate the netting, but it is easier and more cost efficient when the net enclosure structure is integrated with trellising systems at planting. | Slide titled “Net Enclosures Expand in Washington” contains aerial images of netting over sections of orchards. |
| These full block enclosures have been shown to have many benefits. They reduce heat stress, not only to the fruit, but to the trees. They can improve fruit size and skin color. People working under the netting have also commented how it reduced their heat stress and exposure to UV throughout the day. It allows equipment to access it for both chemical management and pruning or any orchard maintenance. It’s been shown to exclude birds and deer. | Slide titled “Multiple Functions” contains an image of a netted orchard as well as a checklist outlining the benefits of netting. |
| But what we want to know is can it exclude insects? | The text “Excludes insects?” appears on screen. |
| So to determine the effects of these full block enclosures on apple insect management, we used a WSU research orchard to test three different treatments. One was a shade net cage covering conventionally managed trees compared to treatment two, which was just conventionally managed trees with no cage, and then treatment three as a control of no treatment at all. We did this at two scales the small trial which was a three tree plot and a large trial was a four eight tree plot in the small cage we had 10 replicates of each treatment and in the large trial we had four replicates of each treatment. | Slide titled “Materials and Methods” contains a bullet point list outlining the three treatments used in the study as well as images of the small and large cages. |
| This experiment was done over two field seasons during 2016 and 2017. The blocks that we chose already had a large resident population of codling moth. So to determine the effects of the treatments, we used pheromone traps in each plot to monitor codling moth abundance throughout the season. | Slide titled “Moth Exclusion” contains images of a codling moth trap within a tree, codling moths stuck to the sticky card of a trap, and an apple with codling moth damage. Text to the left outlines the factors of the codling moth exclusion. |
| We also want to take a more holistic approach to see what effects our treatments had on other indirect pests and their natural enemies. So for this, we chose to look at the woolly apple aphid and its suite of natural enemies, including its parasitoid, Aphelinus mali , and then predators, lacewings, syrphids, and earwigs. | Slide titled “Effects on Indirect Pests and Natural Enemies” contains images of a syrphid fly, wooly apple aphids, and a larval lacewing. Text above these outlines the research question, the indirect pest, and the natural enemies used in the trial. |
| To determine the effects of these treatments on the woolly apple aphid abundance and its natural enemies, we used a variety of sampling techniques. For earwigs, we used a cardboard band around the trunk of the tree. For the parasitoid, we used a yellow sticky card. And then for the predators, which were lacewings and syrphids, we used a white sticky card with a plant volatile lure to bring them in. And for woolly apple aphids, we just conducted time counts on the trees themselves. And this was done every two weeks. | Slide titled “Density Tracking” contains images of a cardboard earwig band around the trunk of a tree, and sticky cards placed within the tree. Text above these outlines the trap deployment and replacement across the trial. |
| So what did we find? Well, here I’m going to show you the results from this trial and just the large cage experiment. And that’s because they’re almost identical to the small cage experiment. On these graphs, on the y-axis, we will have the average cumulative insect counts, and on the x-axis, we’ll have our three treatments, which were cage, conventional, and control. The left or red bar will be the results from 2016, and then the black or right bar are the results from 2017. So here in this upper left graph, we have the results for the parasitoid Aphelinus mali. | Slide titled “Natural Enemies – Large Cage” contains two bar graphs of the mean parasitoid CTD and mean earwig CID for the three treatments used in the trial. This data is shown for the 2016 and 2017 seasons. |
| As you can see in the cage, there were significantly more parasitoids captured than either the conventional or the control so the netting is not having a negative effect on them. In the lower right graph we have the results for the earwigs. In 2016 we had lower counts for both the cage and conventional treatments, but in 2017 they kind of went up in all treatments and there was no significant difference showing that the netting is not really affecting earwigs either. | |
| However, for the generalist predators, lacewings and syrphids, there was a different effect going on. For both years within the cage treatment, there were significantly less compared to the conventional and the control. And this shows that the netting is having an effect and excluding them from the plot. And when you lose two groups of generalist predators, there’s usually an effect on the indirect pest. | Slide titled “Natural Enemies – Large Cage” contains two bar graphs of the mean lacewing CTD and the mean syrphid CTD for the three treatments used in the trial. This data is shown for the 2016 and 2017 seasons. |
| Which in this case was a large outbreak of woolly apple aphids. Here I included both the small and large trial graphs just to show how similar the results were when you took out these predators. In the left graph is the small cage and the right is the large cage. And as you can see for both 2016 and 2017, there were significantly more aphids in the cage plots than the conventional or the control. | Slide titled “Indirect Pest – Woolly Apple Aphid” contains two bar graphs of the mean woolly apple aphid CID per plot for the small cage trials, and the mean woolly apple aphid CID for the large cage trials for the three treatments used. This data is shown for the 2016 and 2017 seasons. |
| Despite the effect on natural enemies and the secondary pest, the netting did have quite an impact on codling moths. Here again are the small and large cage trials. In the left graph we can see the codling moth capture accumulated for both years, and in the cages there was hardly any capture and significantly less than the control, whereas in the large cage there was a little more capture, but still significantly less than the conventional or the control, showing that the netting is having an additional benefit of reducing codling moth adult abundance within the netting. | Slide titled “Codling Moth Capture” contains two bar graphs of the mean codling moth CTD for the small and large cage trials across the three treatments. This data is shown for the 2016 and 2017 seasons. |
| And when you reduce abundance, you also reduce the amount of damage. So here are the same graphs, but depicting percent codling moth damage right at harvest. So here in the left graph, we have the small cage, three treatments, and the right graph is the large cage with three treatments. And they almost mirror each other by both showing that the netting significantly reduced codling moth damage even more than conventional pesticide applications alone. | Slide titled “Codling Moth Damage” contains two bar graphs of mean pre-harvest percentage of codling moth damage for the small and large cage trials across the tree treatments used. This data is shown for the 2016 and 2017 seasons. |
| So those two experiments showed that full net enclosures can reduce codling moth abundance and damage. But we didn’t get codling moth down to zero, even with the addition of chemical applications. So what we wanted to know is, were the codling moth that we were catching in those experiments from an outside population moving through the netting, or was it from a population that already existed within the caged area and was just perpetuating? So to determine this, we tested two treatments. One, a cage, which we use the small cages that cover three trees, versus a control of no cage. And we had five replicates in 2018 and four replicates in 2019. | Slide titled “Codling Moth Migration and Netting” contains images of two small netted enclosures in an orchard, and a codling moth resting on the netting. Text to the right outlines the two treatments used in the trial. |
| The goal of this experiment was to determine if codling moth could move through the netting and was it direction dependent. So could codling moth move from outside of a netted plot to inside a netted plot through immigration, or inside the netted plot to outside the plot through emigration? | Slide titled “Direction Dependent” contains a diagram of a small netted enclosure with three trees inside. A picture of a codling moth with an arrow pointing into the enclosure is labeled “Immigration” and a picture of a codling moth with an arrow pointing out of the enclosure is titled “Emigration”. |
| This experimental orchard already had a high abundance of wild codling moth, so if we caught one, we couldn’t tell if it came from inside or outside the plot. To solve this, we used sterile codling moth, which come with a red dye that they’re fed on and helps you to identify them when you squish them. We also incorporated the use of fluorescent powders that you could see under UV light. And this was to distinguish between which treatment we released it in, and if it was released for inside or outside the plot. | Slide titled “Marking Moths” contains images of red powdered dye, a sticky card with many codling moths attached, and a codling moth under UV light. |
| So from this experiment, what did we find? Well, here’s a graph of codling moth emigration. So we released codling moth inside the cage plot and inside a control plot, and then we captured them outside of it. And on the y-axis is the average number of codling moth that we caught per trap. The x-axis is our treatments, which were a cage and a control. | Slide titled “Out of Plot” contains a bar graph of codling moth emigration showing the average number of codling moth per trap for the two treatments used. This data is shown for the 2018 and 2019 seasons. |
| The left bar in red is what we got in 2018. The right bar in black is what we got in 2019. So as you can see in 2018 we captured fewer codling moth outside the cage treatments than outside the control plots. Whereas in 2019 there was no difference with a significant reduction in the amount of codling moth we recaptured in 2019. So what this shows is that codling moth released inside the cage can fly through the netting and be captured on traps outside of it, although a little bit less than if there was no netting at all. | |
| Whereas on this graph is the codling moth immigration. So we released codling moth outside the cage or outside the control plots and tried to recapture them within the plot. So same 2018, 2019, red, black, respectively. And the y-axis is still the average number of codling moth that we caught. X is our two treatments, cage and control. So this shows a much more striking difference. In the cage plots, we caught only one moth in 2018 and none in 2019, where we had a pretty good capture in the control plots. So this shows that the codling moth really did not move back into the plots through the netting as efficiently. | Slide titled “Into Plot” contains a bar graph of codling moth immigration showing the average number of codling moth per trap for the two treatments used. This data is shown for the 2018 and 2019 seasons. |
| So from the codling moth immigration emigration trials, we learned that the codling moth could move from inside a netted plot to outside of a netted plot, even though it was hindered a little bit. but really almost never moved back into the netted plot. So going back to our original experiments, we’re still trying to determine if the moths that we caught were due to an internal reproducing population or just those few moths moving into the plot. And if it truly is a barrier from them moving in, can we use shade netting alone as a control strategy for a newly established plot that doesn’t have any codling moth in it? | Slide titled “Shade Netting Alone” contains an image of a large netted enclosure in an orchard. Text above this outlines the two treatments used. |
| So to test this, we move back to our large cage trials and we wanted to test our two treatments, a cage, which was just netting and no other treatment compared to a control where there was no treatment and their effects on codling moth density. | |
| Now these large cage plots already had an established population of codling moth in them from years of being an experimental orchard without being under conventional management. So we spent the majority of 2018 sanitizing these cages through measures such as putting up the netting well before bloom and keeping it up just before snowfall. | Slide titled “Plot Sanitation and Re-establishment” contains images of codling moth bands being applied to the trees, codling moth larvae within the bands, and the netting over the orchard. Text below these notes the removal of all fruit in June of 2018. |
| We also put cardboard bands around the trunks of trees to catch any calling moth pupae and larvae and prevent them from completing generations. And we removed all the fruit in the middle of June to prevent the second and third generation from being complete as well. We also tracked the adult abundance throughout the year using a delta trap that was baited with the codling moth pheromone and tracking these larvae and pupae numbers throughout the year to see if our efforts were working. | |
| Here are results from 2018 to see if the sanitation was actually effective. On the y-axis, we have the average number of codling moth adults that we captured, and on the x-axis is there two treatments of cage and control. In this case, the left bar in red represents the capture that we had before we removed the apples, and then the black bar on the right is how many we captured after removal of apples. And we removed apples in both the cage and uncaged treatments to keep it equal and comparable. So here we can see in the cage before we removed apples, we were catching quite a bit of adult codling moth. However, after there was a significant reduction, and this is the accumulation of both the second and third generation, whereas this is just the first generation. so we have a significant drop off in adult capture whereas in the control it’s only a slight drop off in capture when we removed all those fruit likely because moths were moving in from other plots nearby. | Slide titled “2018 Results” contains a bar graph of the mean codling moth adults per plot for the two treatments used in the trial. This data is shown for the pre-apple removal and post-apple removal periods. |
| Here are results from the codling moth cardboard bands around the trunks of trees. So looking at the number of larvae that we caught per plot, the y-axis is the average number of larvae the x-axis is our three generations first second and third and the second and third were after apple removal, whereas the first was before. The bar on the left in red is the number that we caught in the cage. The bar on the right in black is the number that we caught in the check. So before apple removal, you can see we were catching quite a few codling moth larvae per band in both the cage and the check. But immediately after that removal, like we would expect, getting rid of the host, the second and third generation almost didn’t exist. So what we can summarize from this is that based on the adult codling moth capture and the larvae capture, these plots had been sanitized and the codling moth population within them became almost non-existent. | Slide titled “2018 Results” contains a bar graph of the average codling moth larvae per variety per plot for the three codling moth generations. This data is shown for each of two treatments used in the trial. |
| Now that we have the sanitized plots from 2018, in 2019 we kept the same treatments and wanted to see if the netting by itself could provide effective control for codling moth by preventing reestablishment. So to test this we put a codling moth pheromone trap in each plot and we also did a pre-harvest damage evaluation. | Slide titled “2019 Plot Re-establishment” contains images of a delta style coding moth trap, codling moth damage on an apple, and a codling moth resting on the netting. Text above these notes that there was 1 delta trap placed in each plot. |
| Here are the results for the adult codling moth capture. On the y-axis we have the average codling moth per plot and the x-axis is our dates. The black bar on top is the capture in the control plots and the red bar on bottom is the capture in the cage plots. So as you can see, as we enter the first generation of codling moth, the capture in the control was about nine times as high as the capture in the cage, showing that the netting was a barrier, but not a perfect barrier to immigrating codling moth. | Slide titled “2019 Results” contains a line graph of the average codling moth per plot from April to May. This data is shown for each of the two treatments used. |
| As we continue to look at the rest of the season, we can see that by the second and third generation, the differences between the treatments disappeared. And from this what we’re gaining is that these few codling moth that entered the cage plot in the first generation were able to reproduce as effectively as all of these codling moth that entered the control plot and basically caught the populations up to each other to mirror each other throughout the rest of the season. | Data from June to September appears on the graph. |
| We found very similar results with the codling moth damage in the plots. So here on this graph, the y-axis is the average percent fruit damage per plot, and the x-axis is our two treatments, cage and control. This graph represents just the first generation codling moth damage. So these counts were taken around the middle of June, just after the first peak in adult abundance. And here we can see there was about three times as much damage in the control as in the cage plots, which makes sense since there was about nine times as many adults in the control plots as we found in the cage plots. | Slide titled “2019 Results” contains a bar graph of the average percent fruit damage in the first codling moth generation for the two treatments used in the trial. |
| However, as the season progressed and the differences in adult abundance disappeared, so did the differences in percent codling moth damage. So here on this graph is showing the pre-harvest codling moth damage, so after all three generations were complete. And as you can see, there was no longer a difference between the cage and control treatments. There was actually a little bit more damage in the cage plots. | Slide titled “2019 Results” contains a bar graph of the average percent fruit damage at pre-harvest for the two treatments used in the trial. |
| So from this experiment, we learned that netting can serve as a barrier to external codling moth, as shown by the drastic reduction in the first generation. But we also learned that if just a few codling moths get into an untreated plot, they’re able to fully colonize it by the second and third generation. So netting would be an effective tool in combination with other techniques for codling moth management. | Slide titled “2019 Results” contains a line graph of the average codling moth per plot from April to September. This data is shown for each of the two treatments used in the trial. |
| The research shown to this point had only been done on a WSU experimental research plot of about half an acre, and we wanted to know if the same results that netting could inhibit codling moth immigration would occur at a commercial scale. Fortunately, we had a nearby orchard collaborator who offered to let us use some of their netted plots to test this same idea. This time we incorporated three treatments. We had the full net enclosure, just pictured here in the upper right. We also added a block that had just overhead netting to see if netting of any kind could deter codling moth immigration, and then we compared it to a check where there was no netting at all. | Slide titled “2019 – 2020 Commercial Scale” contains a text outline of the treatments, replicates, and release dates for the trial, as well as supporting images of a netted orchard and codling moths within traps. |
| We replicated over time by releasing codling moth every week outside the plot and capturing within the plot every week. As you can see, we released for July, August and September. | |
| Here’s an overview of our trapping and release setup. As you can see within the plot, whether it was netted completely in overhead netting or a control with no netting, we had the trap set up around the perimeter and one at the center. And then we had release points in the bordering orchard all around it as well to see if the moths would fly from outside the orchard and be trapped inside the orchard. | Slide titled “Trapping and Release Points” contains a diagram of the trap layout and moth release points within the netted plots. To the left are images of top-cover only and drive-in enclosure netting in orchards. |
| Here are the results from those experiments. The 2019 results from the upper left on the y-axis, we have the percent recovered sterile moths that we released, and the x-axis is our three treatments. As you can see, the full cage had the lowest capture of recovered moths, while the overhead had slightly less than the check. This shows that netting of any kind has some effect, but the full cage has the most effect on reducing the number of immigrating moths. | Slide titled “2019 – 2020 Results” contains two bar graphs of the percentage of recovered sterile moths for the treatments used in the trial. This data is shown for the 2019 and 2020 seasons. |
| In 2020, we only had two treatments. We were unable to include the overhead netting. We have the same axis of number of recovered moths in our treatments. And here you can see the cage did have a significant reduction in number of recovered moths. And what this shows is that even at a commercial scale, full netting does inhibit moth immigration, but not completely to zero. | |
| From these five years of research, we have learned a lot about netting and codling moth control. We’ve shown that full enclosures can prevent a significant portion of moths moving in from neighboring blocks. And when combined with conventional management, netting significantly enhanced codling moth control. However, if a few moths are able to get into an untreated plot, they are able to establish large populations quickly, even under netting. And netting has the potential to exclude natural enemies like lacewings and syrphids, which can lead to secondary pest outbreaks. | Slide titled “Shade Net Discussion” contains text outlining the key results of the studies, as outlined in the audio. |
| While we’ve been looking at netting for codling moth control in Washington since 2015, researchers in Europe have been doing it for about a decade longer. It began in apples in 2005 when growers decided to modify their hail net structures to be enclosures to help with codling moth management since they were applying over 12 insecticides a year and still getting high levels of damage. They then adapted this in pair in 2008. And they decided to test two different structures. One was the row cover shown here and then a full block enclosure here. | Slide titled “France and Italy Experience” contains bullet point list of the features of the apple and pear trials mentioned in the audio. Below this are images of row cover and full block netting in orchards. |
| These studies were conducted in France and Italy, and they found very similar results to what we found. These charts show percent fruit damage by codling moth and oriental fruit moth, and here on the left is France apple studies in 2011 and 2012, and on the right is studies in Italy on pears. The light blue bars show the damage in unnetted plots, and then the left bars are unnetted. As you can see in both apple and pear, the percent fruit damage was dramatically reduced for those pests. | Slide titled “France and Italy Pest Management” contains two bar graphs, one of the percentage of damaged fruits by codling moth and oriental fruit moth in netted and un-netted blocks in French apples, and the other showing the mean value of the pears in netted and un-netted blocks in Italy. Text below these outline the major results. |
| They did note that the full whole orchard enclosures like we use here in Washington were less effective than the row covers that they used. They also did not have outbreaks of other pests and diseases except for a couple cases in France where both rosy and woolly apple aphids required in additional insecticide control in some areas. Now these results are 10 years old but they are almost identical to what we are finding and hopefully we’ll get an update from them soon about more recent results. | Text noting that full orchard enclosures were less effective than row covers is highlighted. |
| With that, I’d like to thank everyone who helped with this project. My advisor at the time, Dr. Betsy Beers and her lab crew for helping build these structures and do all the sampling. | Acknowledgements slide contains an image of the Beers lab employees. |
| I would also like to thank the funding sources that provided the supplies and help for this research to be conducted. | Acknowledgements slide contains the logos of various funding sources for the project. |
| Here are my references throughout the talk. | References list is shown. |
| Music plays. | Credits for presentation and video production roll. |
Link to YouTube video: Codling Moth-Netting
