Optimizing Blackberry Pest Management: The Impact of RCA Trellising and Spray Coverage

In this episode of  Arkansas Food, Farms and Forests, we discuss a study on the interaction of trellising type and spray coverage in blackberries.

Aaron Cato, an extension specialist in the horticulture department focusing on integrated pest management, shared details about his latest research and related studies that looked at the impact of the rotating cross-arm trellis on pest management in blackberries focusing on the spotted wing drosophila infestation. 

The research found that the RCA trellis provided better pest control than the traditional t-trellis. The data also revealed insights into the effects of microclimate on pest infestation and emphasized the need for cultural controls alongside insecticides.

Read the Research: Impact of trellising on spray coverage and spotted-wing drosophila infestation: comparing the rotating cross-arm trellis to the T-trellis

Related Studies: Rotating Cross-Arm Trellis Offers Improved Yields, Quality for Blackberries

Related Links:
Recommendations for RCA Trellis for Blackberries

Department of Horticulture 

Dale Bumpers College of Agricultural Food Life Science

Arkansas Agricultural Experiment Station

Arkansas Cooperative Extension Service 

U of A System Division of Agriculture 

Transcript

[00:00] Intro/Outro

Welcome to the Arkansas Food, Farms and Forests Podcast, the podcast bringing you the latest on food, fiber and forestry research from the Arkansas Agricultural Experiment Station. The research arm of the University of Arkansas System Division of Agriculture.

[00:18] Jenifer:

Welcome to Food, Farms and Forests. I'm Jenifer Fouch. Today we are discussing the interaction of trellising type and spray coverage in blackberry. More specifically, we're learning about a study that looked at the impacts of the rotating cross-arm trellis on pest management in blackberry. To talk to us about this research is Aaron Cato, extension specialist in the horticulture department focusing on integrated pest management. Aaron, thanks for being here with us.
 
 

[00:46] Aaron:

Yeah, thanks for having me on, Jenifer.

[00:48] Jenifer:

It's blackberry season, so there is no better time than now to discuss this research and this tool. The publication is titled “Impact of Trellising on Spray Coverage in Spotted Wing Drosophila Infestation: Comparing Rotating Cross-Arm Trellis to the T-trellis.” So, Aaron, I know you have been involved with research related to trellising systems before. This one looked at the use of RCA and how effective it was for pest management, specifically for this species of a type of fruit fly. Is it?
 
 

[01:23] Aaron:

Yes, yes, it's actually a big deal in the US because it was an invasive fruit fly came over here, and around 2013 or so. So, it's a big deal in our blackberries and blueberries, and especially here in Arkansas.

[01:35] Jenifer:

What about this latest study, this specific research, makes it unique?

[01:40] Aaron:

Yeah. So, I think it's, unique and also kind of very specific here to Arkansas and UADA. 
 
 So, we didn't develop the RCA is actually developed in the USDA, by Fumiomi Takeda. I think around 2010 or 2013 or something; I'm not as privy to the exact origin. But Amanda McWhirt, who is our production specialist for horticulture, kind of brought it back up from the dead. And it's a trellis system that was typical, was designed for people wanting to grow blackberries further north so you can rotate it to the ground, put a cover over it, and actually prevent losses per winter injury, which, if you've been in Arkansas the last 3 or 4 years, is a pretty big hot topic because it keeps getting into the negatives in the winter. 
 
 And so, Amanda started working on this. I think about 6 or 7 years ago. I came onto the scene about five years ago, and she was trying to get it not only for the wider side for winter entry but also to improve fruit quality, which is one of our biggest issues because we get so many rains in the summer, which is bad news for good quality blackberries. And so, she had a student; her name was Erica Henderson. She used to work here in the System as well, at our fruit station. And they were looking at all different types of stuff. They were looking at fruit quality. They were looking at just how much yield these two trellises kind of produce. 
 
 And one aspect they kind of had me helping with, kind of advising on, was insects, in fact. And Erica actually found less of these Spotted-Wing Drosophila on the RCA trellis, which is the one that we rotate over. It's actually a movable canopy versus the T-trellis, which is the normal trellis that's used across the majority of the Southeast and Midwest, the growing regions of the country. 
 
 And so, really, this study is all about trying to figure out: why is the RCA giving us this benefit? Because we don't use the RCA for pest control, we use it for fruit quality, and we use it, especially for winter … for winter injury or impact from winter. And so, that's really what we were trying to answer and trying to figure out is: what aspects of it kind of are driving home that pest control?

[03:44] Jenifer:

So, what did you find out? What were the key findings from the research?
 
 
 

[03:48] Aaron:

Yeah. So, I actually published on the aspects of spray coverage, but we actually had another student, Mattea Duncan, who was looking at kind of the environment. 
 
 And so, I'm an entomologist by trade. So, insects are what I normally dabble with. One thing we always think about with insects is the microclimate or what's going to make them happy or unhappy within a crop canopy or just within a crop. 
 
 And so, when we found out that we had less spotted wing drosophila, we started to ask ourselves, you know what? What lends itself to this? And so, the first aspect is kind of what Mattea Duncan looked at, which is the idea of a microclimate. We know that the RCA has a smaller canopy, and it's more exposed to sunlight, especially on the backside, and then it kind of creates a shaded environment for fruit on the other side because it's planted on north to south rows and so that when the sun comes over, and actually shades the berries the whole time. 
 
 So, what we thought was that this was going to play against some of the aspects of spotted-wing drosophila. These are flies that are native to China. They really love high humidity. They don't like the heat that much. They can deal with it. They're in Arkansas. They're south of here in Georgia and places like that as well. But they don't like it. And so, they only lay eggs at dusk and dawn for that reason. And they don't like the sun that much. They don't like a lot of light penetration. And that's why a lot of times they will actually leave the blackberry canopy and go to like a surrounding tree line to hang out or to kind of survive the day. And then, as the sun comes up or goes down, they will actually come back out into the canopy to lay eggs, which is the big no-no for us and for growers. 
 
 Whenever you have a thinner canopy that's more exposed to the sun, we think that's going to increase light penetration, which is something the spotted-wing does not like. We also think it's going to increase the ambient temperature and decrease humidity. And so what you found was it did do that decreased humidity and increased the amount, the actual ambient temperature. And so, when they were finding more or less spotted-wing in the RCA, it's probably due to microclimate. 

 But the other aspect is really what my study looked at, which is if you have a thinner canopy, are you having better success at actually getting insecticide side into the canopy and protecting against spotted-wing drosophila? 
 
 So, spotted-wing drosophila is a pest that requires a full spray schedule. So, people have to spray every single week. And if they don't it gets into a disaster situation. And so one aspect of every spray application is how much spray coverage did you get. Successful spray applications only work out if you get above somewhere like 15 to 20% coverage on leaves and berries and things like that. 
 
 And so, what we found was that if you vary the amount of water that you put into a canopy, the spray solution or some spray output is what we would call it, then you actually may not yet have that successful application. And so what we did was we varied the amount of, spray output or the amount of gallons per acre we were putting out. And we looked at it across two different trellising types. 
 
 So the rows heading cross arm trellis, which was a much thinner canopy, which has very exposed berries. They're in the shade, but they're all on one side of the canopy versus the T- trellis, where it's a kind of a thicker canopy, probably more like three foot 3 to 4 feet in width, whereas the RCA is probably one foot in width. So you can imagine there's much more air movement in there. and so we actually found some pretty striking, pretty stark differences in the amount of coverage we were getting with similar amounts of spray output. And so in any crop that you grow and, for food, that's always going to be a way that you can maximize pest management.

[07:20] Jenifer:

So you found you were getting more sunlight, more heat, and then more coverage with pest management?

[07:27] Aaron:

Yeah. We didn't look at the sunlight. We haven't published on that. But we did look at it to some degree. But yes, there are higher temperatures. It's lower humidity. It doesn't  always play out to be exact, but the averages make sense. And what we found was more specifically is that if you used a lot of water, you saw no differences. 
 
 So we would say, I mean, it's kind of lingo for farmers and researchers like GPA, the amount of gallons of water per acre. And so we recommend somewhere like 60 to 80 gallons per acre. What we found is that when you put out 60 gallons per acre, we got good coverage in both the RCA and the T-trellis. However, we got better coverage in the berries on the on the RCA regardless, because they're not in the center portion of the canopy, they're almost always on one side. 
 
 You don't have to get a bunch of water into a canopy to cover a berry on RCA, because it's not in the it's on the outside. whenever we reduce the amount of carrier volume, we saw pretty big differences. So as you reduced it, we didn't get half as good of coverage. On the other T-trellis, the bigger canopy. But on our RCA, our rotating cross-arm trellis. Even when you reduce it, we still kind of have the same amount of coverage, which means that us, we can probably get by or something like 40 gallons per acre instead of 60. We think it's just something that's going to create more of an efficiency. If you're using a trellis system like the RCA that already has these aspects where it doesn't need as much carrier volume, then it's more likely that people are going to have successful applications across the board. and that's what we think we'll see in the future is just, you know, less spotted wing total. 
 
 But the other thing that we did that I kind of have mentioned is that we just kind of redid what Erica Henderson and Amanda McWhirt did in the beginning. They looked for eggs on, spotted-wing drosophila, eggs in berries. We looked for larvae. So, we actually went the next step and we found the exact same thing. Regardless of what spray material you put out there, there were less larvae in the RCA. I think it was on average like one every 40 berries versus something like one every ten berries in the T-trellis. So, you know, it's like a, you know, we're fourfold decrease or something in the number of spotted-wing that were in berries, which is a huge amount of pest management or effect pest management for a grower when it's just the trellis system that's that's really doing that.

[09:41] Jenifer:

Yeah. That's impressive. What do these results mean then for producers or what do you think they can take from it. That is something that they can be useful in the field.

[09:51] Aaron:

Yeah. I think the overarching, thing that I hope that everyone takes is that there's more than just insecticides to control a pest like this. And I would say that last year and 2021, we had really, really bad spotted-wing drosophila years. And so it's like I said before, a spotted wing-drosophila really loves it to be a bit more humid, a bit cooler, and a lot of cloudy rainy conditions. In 2021 we had growers all across the state that had outbreaks of us bottling in berries. They were selling it, people were complaining to them and they were spraying every seven days. And so it really showed the growers that you can't just spray and then forget about it. You have to rely on cultural controls. And there's a number of them that are very impactful. 
 
 And we recommend every year, which is picking a little bit or often you even like, trying to get berries into the cold storage right away. When it comes to winter time, prune out as much plant material as you can. So to increase, open up the canopy and let more light in, let more heat and things like that.
 
  And the other one that we were trying to really showcase with this is trellis.ing. So, when you're going to put out some new, land or some you're going to put out some blackberries, you can choose a trellis that's going to help you along the way. I think our growers are kind of getting used to this idea of air movement in the canopy, how open it is and how much that means not just for bottling control, but for all types of pests. almost every disease that we work with is a function of leaf wetness, along with the leaves are wet. The more humid a canopy is, the less wind that can come in and the more disease you see. There's the same thing was spotted winning. And it's not all insects are that way, but this one is because it is such a function of light intensity or light, not light coming through and the amount of heat and humidity. 
 
 And so, I really hope that growers kind of see that where especially in specialty crops, you have to rely on your cultural controls to have a long-term approach to best management. 
 
 The other aspect is just thinking about the amount of carrier volume you're using and making sure that you're calibrated correctly. 
 
 And so overall, hopefully, it just kind of makes growers look more at this idea of making an application. what can you do to make it more successful? I'm actually working with Jason Davis. He does a lot of drone spraying and things like that. And we're actually getting funding to actually look at drone applications and blackberries and other specialty crops. 
 
 And so, you know, hopefully, growers will just look for more than just what they've done in the past and try to integrate some newer techniques, or even just things like trellises to try to impact the test outside of just using insecticides. Because as spotted-wing Drosophila is becoming resistant to insecticides. So you can't rely just on those things alone, or you're really not going to be able to keep them out of folks berries in the future.

[12:34] Jenifer:

So, the t-trellis is the more traditional one that is more commonly used. Is the RCA more expensive, more challenging, or just not as common? Why? You know, why do more people use T-Trellis? Are we just now making a move to move to the RCA?

[12:53] Aaron:

Yeah, that's what a lot of the man in the arts research is looking at and know she's for years tried to show, really she's modernized the pruning aspect of it, which is what's been the thing that's held it back the most. 
 
 And so, the RCA, it's a rotating cross arm trellis, and that means you're rotating a woody perennial plant, and between me and you, we both know there's a lot of shrubs out there. You're not going to rotate around, and blackberries are more a trail... we have semi-erect, which is what I know a lot of Arkansas is famous for, breeding but they are more erect in general blackberries. 
 
 But what you used to have to do is go train one cane sideways, and you got that every several times a week and train it to go one direction and grow it another direction. It's a lot of work. It's a lot of hands-on work. And if you ask almost any blackberry grower out there what their major hold-up is in production, it's probably labor. And so what do you tell someone to use a trellis that's going to be need more of their biggest issue. They're just probably not going to use it. 
 
 But Amanda actually has pioneered a different way of training on it where she calls the fan method. I think that's what the phrase she uses now. It takes, you know, a quarter of the work. It's a little bit more hands-on activity than a regular, operation, but it's really not that much more. And so, what she's been able to do is get this trellis system that has all these benefits and take away some of the downsides and what they're she's finding... She's working with some of our other colleagues like Rene Threlfall. She's in fruit science. They're finding just the amount of fruit quality or the increases in good quality fruit pays for the any amount of extra labor that you're going to have to use for this trellis. 
 
 And so ,people are putting it out now, they are getting a lot of savings from it. And it's taking hold in some areas. 
 
 But the t-trellis is not you know, it's no schmuck on the other end. It's got some positives compared to some of the older trellises. And so, it's still really useful because it is cheap. It's cheap to put out and cheap to maintain. You can reuse it more often. 
 
 The RCA it's we're still working out the kinks, is what I would say. But we have several growers in Arkansas and there several growers up in Saint Louis, some in Alabama, some in Georgia, North Carolina. You know, these are all people that have seen University of Arkansas publications and tried it out, and especially those who are working on a smaller scale, like, you know, 3 or 4 acres, that's no small amount of blackberries. But, you know, that's the kind of operation that can think about something like an RCA and use it. 
 
 But we also have growers with hundreds of acres that are putting out the majority of RCA. So it's taking hold to a good degree. But we've also had a lot of like, really good successes that are kind of on the record.
 
  There's a farm just south of Fayetteville, Rivercrest Orchard, whenever it got down to like -16 or something. And they, I think that was 20, 21 or whatever it was in February, they did not have enough row covers to cover all of their RCA blackberries, but they covered some and didn’t others. So, you can look on one single row and they would have blackberries that were alive versus completely dead. Now I say dead They came back the next year, but they had zero fruit off those berries that year.
 
  So you ask yourself, what is the savings when you have zero fruit versus something like 70% of what you would have normally? They were one of the only places around the town that had fresh blackberries that year because they use this RCA system. So if you ask Magaras they'll tell you: why would they plan anything else? Because in the bad years, they have berries, and no one else does. So it paid for itself for, I don't know, 5 or 10 years more after that. 
 
 So that's kind of what we've seen with this new system. It has headaches and growing pains. But when people get a few years under their belt, they understand it. Something has happened more than just the fruit quality of average. So, there's usually something that puts them ahead of the game. And that's kind of the idea with these cultural controls is they kind of lower your… or they raise your floor. They don't always increase your ceiling, but they raise your floor, which is kind of what we're hopeful for our growers because we're just trying to keep them in business, to be honest.

[16:50] Jenifer:

Aaron, is there anything else about this research specifically or anything else that you'd like to mention that I didn't ask?

[16:58] Aaron:

I would just say that, you know, there's still a lot more for us to learn in this system, and we're hopeful to have a recommendation for growers that if you're using the RCA, it's this amount of spray volume. 
 
 But I would say that we've already created a lot of resources for people to use. So, Amanda actually did publish a guide on rotating cross-arm trellis that's available through the UA or the UAEX publication system. We've published, you know, a couple factsheets on spotted-wing drosophila, on how to go back and check what's out there. 
 
 And so I would just tell people, keep an eye out for some change and recommendations in the future and check out our resources now because a lot of them are very, relevant to what's going on. 
 
 And I would say right now, the most relevant thing is that we got a lot of spotted-wing in the fields. We have really early blackberries, and it won't stop raining. So, growers really need to be on the lookout. 
 
 And if anybody else is listening to this and they have blackberries, I would recommend you go out there and spray for spotted-wing and try to make sure you get a good application that covers it, because you're going to have some little worms in your berries if you don’t.

[18:01] Jenifer:

Aaron. So, Amanda McWhirt was one of the co-author on this research. Are there any other collaborators?

[18:09] Aaron:

Yeah. So, we had Erica Henderson. She helped out with some of the first-year data, and also she just kind of found, you know, the spotted-wing on this in the beginning. 
 
 And then Ryan Keiffer and Lizzy Herrera, they're both some of our program associates who, you know, did a lot of the legwork for this. And, you know, it's more than just legwork, but also being out in the field and bouncing ideas off of them and giving us kind of some of their perspective.
 
 Lizzie's on there. She worked with some of that. But, you know, she actually worked with spotted-wing drosophila for her masters. So, we actually asked her a lot of questions about this because she kind of has a lot of initial experience with the first wave of spotted-wing coming into Arkansas and kind of some of the roadblocks that were created with that. 
 
 And then, Duncan, she's not on this paper, but she was kind of on the sister paper. 
 
 We're working with several farmers across the state and they're always very forthcoming with plants to spray, just to try to figure things out. So, we're always very thankful for the growers we have here in Arkansas. I'm just thankful for everybody in the system that we work with, especially the folks on the stations. So down at the Hope station, I forgot to thank them. I'll thank them again. So, Daniel Rivera's, head of the Hope station down there. Those guys down there and their staff do a really good job taking care of us. 
 
 And then Jackie Lee out at the fruit station, who's helped us a lot with this as well. And so really thankful for the system that we have in place to work at the experiment stations and all training and that kind of thing. So, I think that's all I really appreciate coming on.

[19:35] Jenifer:

Thank you so much for spending some time with us and explaining this research.

[19:40] Aaron:

Yep. Thank you.

[19:41] Jenifer:

That was Aaron Cato, extension specialist in the horticulture department, talking to us about his recent research into rotating cross-arm trellis and how effective it is in pest management and blackberry. Thanks for listening. Jenifer Fouch, don't forget to subscribe!

[19:58] Intro/Outro

The Arkansas Food Farms and Forests podcast is produced by the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture. Visit aaes.uada.edu for more information.