229: Weed Control in Vineyards

Sustainable Winegrowing with Vineyard Team

May 16 2024 • 33 mins

Trying to manage the weeds in your vineyard? John Roncoroni, Weed Science Farm Advisor Emeritus with the University of California Cooperative Extension, Agriculture and Natural Resources covers control practices including biological, mechanical, cultural, chemical, and perhaps in the future, electrocution. Although weeds rarely compete with vines, they can host insect and vertebrate pests and get in the way of pruning crews, increasing labor costs. Listen in for John’s number one tip to better manage weeds in your vineyard.

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Transcript

Craig Macmillan 0:00

Our guest today is John Roncoroni. He is Weed Science Farm advisor emeritus with UC Cooperative Extension, UC Agriculture Natural Resources, and we're going to talk about cultural control of weeds in vineyards today. Thanks for being on the podcast, John.

John Roncoroni 0:13

Now you bet, Creg, thank you for having me.

Craig Macmillan 0:16

We met with we'll start with kind of a basic foundation, what would you say is the definition of cultural weed control? Maybe How does it differ from other forms of weed management?

John Roncoroni 0:25

cultural weed control as part of an integrated pest management program, you know, we have basically cultural mechanical, sometimes they're put together sometimes they're split, we have biological, which is much more important, I think, in insects than it is in weeds. Now, we talk about biological control of weeds just a little bit to show how it fits in with all this too, is that you know, when you see that rust growing on a malba, or cheese weed plant in California, people say, Well, maybe that can control and you can see sometimes it really weakens the weeds. But the one reason that doesn't work here very well as it does in other places is the same reason why we can grow such great grapes and make great wines in California is because it doesn't rain in the summertime, if it rained in the summertime, like it does. In many other areas, that moisture level would stay up and we probably have a better chance of controlling Malba. We do use biological control of weeds in more landscape like range land type at large areas, but really on any kind of agricultural situation where we're looking at control in one spot, it really doesn't work that well. Even with star thistle we be talking about people wanting to put our application of of weevils for start thistle. Well, they're out there, and they're on a larger scale. So that's biological, much more important in entomology than in Weed Science, a chemical control, obviously, the use of chemicals, either conventional or organic chemicals or control. And then we have mechemical or cultural you know, cultural weed control to me is using the utilizing the plants that are there or sheep in areas of the San Joaquin Valley that used to use ducks or geese to pull out Johnson grass rhizomes, yeah, we're utilizing sheep quite a bit more. Now. Of course, mechanical we're looking at when you look at something like a mower, right, a mower is mechanical and cultural because when you mow, you're leaving some plants. So you're mechanically mowing them down. But culturally, you're leaving plant where something like French flower, maybe a blade or or you know, one of the the weed knives are all the different moving wheels, maybe more considered mechanical.

Craig Macmillan 2:30

Let's talk about mechanical a little bit. There was a book I don't know if it's still in print. And it was a SARE book. And it was called steel in the field. And the author's thesis or premise or idea was if you drive around farm country, no matter what the crop is, there's always a graveyard of old implements, just parked just parked there, you know exactly what I'm talking about.

John Roncoroni 2:51

Oh, god. Yeah.

Craig Macmillan 2:54

And his his point was, all of those things were technologies that someone had come up with. And then the individual farmer, probably then made modifications to those for their site for their crop for their soil, then the herbicide era came on. And that wisdom was lost, basically. And the argument was, hey, maybe we can bring that that idea back. And I mean, this goes back to like the 80s, early 90s. It's happening, it's happened. What are some of your favorite technologies in terms of cultivation, mechanical weed control, and some of the limitations, some of the plants that works well with other situations where it doesn't? What's your experience been?

John Roncoroni 3:39

I love talking about that, Creg, is it you know, talking about using mechanical control, and then and then going into chemicals, and now going back, it's almost like I talked to people about chemical control itself. When I started, Roundup wasn't glyphosate was a new thing. And we used it very judiciously. And I tell people, it's almost like, I learned to drive with a stick shift. I had to learn all these other things. Well, after that people learned to drive automatics. Right, because they knew one way to do it. Well, now that we're back to using stick shift, it's a whole lot easier for me, because I remember now people have to read or write. It's, it's the same thing with the mechanical. And when I started a Davis, you know, in the early 80s, we probably first came to work in vineyards in Napa, close to Davis, about 85, 86. And at that point, there was a lot less drip irrigation, a lot more dry farming, and a lot more French plowed. One of the reasons was we didn't have drip irrigation. I mean, we all want deep roots, but you're going to have more shallow roots with drip irrigation. And that was one of the reasons we moved to chemicals away from this big pasture. We always had a blade, right something like to drop a name a Clemens blade, which we all know what that is. It just cuts. You know, one of the problems with that is if the soil is too moist, then it's going to cut and go right back. And there's been a lot of innovation. My colleague Marcela Moretti, a But Oregon State's done a lot of testing with different kinds of machines. You know, one of the things about mechanical or even like mowers is that so few growers have mowers?

Craig Macmillan 5:11

When you say mower? You mean an in row mower?

John Roncoroni 5:13

Yeah, I mean inrow mower. All right. And I'm sorry, I when I talk about weeds in vineyards, because I tell people I've made my whole career out of about three

Craig Macmillan 5:21

Three to six inches.

John Roncoroni 5:24

I have about a foot and a half. Right? Sometimes I'm up to four feet, right. So that's where my whole career is right there. And that we talk about when we talked about what we're doing in the middle is with cover cropping. That's a whole other podcast and probably, I mean, I've done cover crop work over the years with some large IPM grants. I did quite Elmore and some other things. Zalem and Jim McDonald Yeah, no, I'm talking about just under vine we're thinking. Yeah.

Craig Macmillan 5:53

All right we're under vine.

John Roncoroni 5:54

Talk about being a very specific expert - four feet. At the most.

Craig Macmillan 6:01

I got it. I get it.

John Roncoroni 6:02

You know, very few growers are using mowers we have the big bladed mowers and also we'll have a straight trimmer. I was trying to do some string trimmer work, but just using a little weed eater. My old friend, Mike Anderson, who was the superintendent or basically ran the oppo research station said that I could use a string trimmer in one of their vineyards over his dead body. And I was like, you don't want any girdling in those vines. So I know, there's been a lot of apprehension. There are some other kinds of mowers very, very, very few growers have mowers, from what I've just done some surveys, I've done one because you have to go back over and over and over, right? And then everything has been weighed against, well, we can just spray mowers or one, you know, there's several different and I can't remember all the trade names. But you know, there's some of the basic technology. Yes, there's some that do some stirring of the soils, you know, with blades that are perpendicular to the soil, right. So they're, they're stirring it, there's what we used to call and when I worked in bean weed control, Lilla stuns, which are wheels that turn sort of at a 45 degree angle to stir the soil. There's, you know, power driven machines, there's just ones that ride along and there's blades, there's, you know, there are so many, and it really depends on the kind of soil you have, you know, our rocky is sometimes the place where we put grapes are not a place where you could put tomatoes, right in times, shallow soil, hillsides, kind of cultivation, can you can you do cultivation? Can you do light cultivation without getting you know, soil movement? Can you even do it? Is it allowed by, you know, some rules about land use in those areas. So, there's a lot of things that go into mechanical and again, from my perspective, the weeds you have.

Craig Macmillan 7:54

I like this point here, because I think put to put things into kind of a general sense to guide things. We have blades that basically cut just below the surface. So that's cutting off the top of the plant from the bottom of it for certain kinds of plants that will kill it or control it. Then we have things like a French plow, which is a burying it's a true plow. Yeah, it's flipping soil, picking it up and flip flopping it over. Then we have the sturer. So you mentioned that little stun the central lines and other example, sun flowers. That's what they do. Yeah. Yeah. Things like that. My missing one.

John Roncoroni 8:26

mowers.

Craig Macmillan 8:27

mowers, okay. Yeah.

John Roncoroni 8:29

So that, you know, then there are a lot of variations on those combinations. It just amazing for me, and I follow a few of the manufacturers and get to see like on Twitter X, whatever, to see the videos that they're posting on LinkedIn. You know, it's just amazing to me what they're doing and the innovation that's going into those. One of the things that my again my colleague Marcel HomeReady, up at Dr. Moretti up at Oregon State talks about making sure your tractor is big enough for some of these, you know, hydraulic using, right, but one of the things we always used to talk about was, you know, the use of gas well, I know there's a lot more use and we're moving more into electric tractors, and those sorts of things. But when it comes to mechanical, really doing a good job of mechanical weed control with those some of those, you're going to have to have electric or gas you're going to have to have a big tractor. They're not going to be like a you know, a little ATV with a nifty 50 sprayer spraying herbicides right you're gonna need some hefty equipment in a lot of them not always.

Craig Macmillan 9:33

Let's start with weed knife. That's a very popular technology you see it oh yeah all over the place. What are the kinds of weeds that that's good for controlling and under what conditions it doesn't work well and under what kind of conditions does it not work well?

John Roncoroni 9:47

And I don't know the areas and passive as well as I know Napa I was brought a while but I would tell the growers you know, using a weed knife in Carneros you have about four days from when the soil goes from being too wet to being too dry. I have heavy clay soils, it holds moisture and it just. Yeah, exactly. And I'm sure there are areas like that, you know, and it can't, you can successfully cultivate down there, but it's tough, you need the timing, it's so important. If you're going to wet that soil just goes right back with that blade, right you cut through and the roots are able to tell back in, you know, if it's too dry, it's really going to be a rough ride. Because you're not going to go too deep, it's going to work well on some smaller annual weeds, which, you know, a lot of our weeds are, you know, some of the grasses with their net have a root ball sometimes are harder than just a small annual broadleaf plant, you know, you're going to have some problems, especially with something like malware, cheese weed that that grow very large. And depending on when you doing it something like cheese weed is and rye grass and Fillory, while I mentioned them are the first weeds to germinate in the fall. So by the time you get in a little bit later, they may be too big to really do a very good job on.

Craig Macmillan 10:59

Are their soils where we die for it's particularly well?

John Roncoroni 11:03

I would say you know, in less than heavy clay soil and not complete sand, a sandy loam soil, I think that holds some moisture, you know, it was able to get in anything, I think it's not a complete stand or a real heavy clay, they do a nice job, but the weeds can't be too big. And again, it's that timing and you know, with vineyards, it seems to think everything happens at once right time when you may be in having to do some sort of insect spray or mold spray, the same time you should be out there cultivating so just and it takes a while to do a good cultivation job.

Craig Macmillan 11:35

The speed that you're rolling is really important. You want to be slower ride faster.

John Roncoroni 11:40

Well, and Dr. Moretti has done this work there is an optimum speed. If you go too slow, then you really don't do a good job of cutting. If you go too fast, you miss some. And maybe this is where some of the electric AI technology can help. You don't want to cut the vines. Right, so you have this pull away, that keeps the weeds, the weeds will go right next to the vines, which you know can be a problem. We'll be talking about other situations with little vertebrate pets.

Craig Macmillan 12:06

I'm kind of getting astray here a little bit, but I No, no, but I think this is an important question. So choosing what I do and how I do it, we go back to the other technologies, Why care about weeds? Right? Why care about you know, I had I had a vineyard once that had been an oak field. And it was direct planted own rooted sprinkler system that was planted in 1976 I got the vineyard 1993 out of heavy clay soil, and I would irrigate with sprinklers twice a summer, and that oak grass would grow up into the fruit zone up into the canopy. But it would dry out. And it completely choked out everything else I had, I had no other real issues. And we would mow the middles. And I remember people going oh my god, you got all this issue, you need decent herbicide, you think grass out of the middle because the grass is gonna. And like these vines were super vigorous. They were tons of crop. I mean, I had to crop thinner. And so I started asking myself, well, how much competition? Is this really doing? Are there particular weeds that we should see? And you're like, wow, that's gonna be a competitor for water, nutrients and others where we go, No, I don't really want it there. But I'm probably not going to dig my vines.

John Roncoroni 13:13

So Craig, this is the eternal question when it comes to this. And it really depends on where you grow your grapes, right? If your goal is to get 25 tons of grapes, if you're somewhere near Bakersfield won't offend anybody, but they're looking more for tonnage. Right. And I've gotten a lot of flack for using our premium grape situations, we're not always looking for maximum tonnage. Right. And I don't know that the problem with weeds and if you hear me speak about weeds, I rarely have ever talked about direct competition between weeds and grape vines. Now, there are some exceptions, you know, when we were looking at that balance between irrigation and getting the deficit, irrigation, right, getting those maximum flavors into those grapes. So we may be right and a little low with our water in August or September, near the end. And we see that especially, I don't know so much about about I know, part of the areas where we are with the vineyard team there that they gave, we can get these howling north winds, right? Right. And you can in a very short time, you can turn some very great, expensive grapes into really great expensive raisins, right, getting that water in at that time of year. So having any kind of like flu Velen, which is really just covers the whole area of Napa and Sonoma. I know it's moving around some other areas. But you know, people say well, how much water does it use? And my old friend Rhonda Smith used always asked me well, how much water is it used? I go, we don't have crop coefficients for all the crops. It's hard to know which you know which weeds grow, how much water they use. And then the other thing too, is that if we're looking for consistency in a vineyard, and only half the vineyard is covered with that weeds where we're gonna put two too much water in one area and not enough in the other. Isn't that different? So it's competition for that sort of thing. And of course, young vines, right when we have young vines with big weeds and that that oak grass that you had, if you had young vines, you probably wouldn't have to be worried about being a grape grower very long, right?

Craig Macmillan 15:17

You have seen that young, really healthy barley cover crop?

John Roncoroni 15:21

Oh, yeah, it's it's tough for first three years. But like talking about establishments, it's really important, no matter what you do to keep the grapes sort of weed, not weed free, but really keeping the competition down. And then late in the summertime, but the rest of the time. It's other things that I've talked about these, it's one of those things where you ask people, you know, raise their hand if they have this problem. It's 50%. Yes. 50%. No. And that's voles. And I tell people, I thought that when I was in Napa, I think 30% of the growers do weed control strictly for vole protection. Because those nasty little marmots can they can girdle a grape. And I know one vineyard and Carneros they couldn't get in and do some work. Someone told me that one year they lost one in five vines. Wow. And they're not coming back. Right? That's, that's bad. Yeah. So you know, it can be a problem. We found this when we were working with mow and blow technology years ago, looking at cutting cover crop and throwing it on the vine. The Weed control was fantastic. But in my whole time, working in vines from 1985. And, you know, until today, I've never been in a vineyard, except in this trial, where I saw voles running between the rose in the middle of the day. Right, they were just happy there was so many they kind of had to get out just to get a breath of fresh air, they use those tunnels, you know, just runway so that they were protected from that, you know, the birds of prey, which you know, can help. And I people always ask about that. But again, we have that pest and prey cycle that the voles may come in and do a lot of damage, before they get a chance to be taken. And then it depends on what your neighbors doing and how effected the birds are. This is a question that I our new vertebrate pest person, Brianna Martineco in Napa who she took my office, not my place, right. So we we about a weed scientist. And one of the questions I've asked is, you know, how much of an area around the vines? Do we have to keep clean, so that the birds have a chance and the voles stay scared? You know, that's kind of question, you know, especially as an emeritus, you can ask these questions. And, you know, let the new people answer them. You know, the other thing and I've talked about this is in a rare occasion, you know, one of the things that we do you see people, anytime I'm out in the field later in the season, I talked to a grape grower, while we're out there, they're pulling those leaves off so they can get more air movement. Well, if you get some tall weeds like that, you know, the oak grass that was growing, you know, are you going to have restricted air movement? Are you going to have higher moisture content? Is that going to increase your pathogen pressure it can, doesn't always happen. The other thing too is having, you know, high grass can cause in frost prone areas, you know, if you're not getting that radiation from clean soil, and that's in the middle, not so much under the vines, you know, we can have that and sometimes on young vines near the vine itself, getting that reradiation, but again, you know, as I like to tell people, you're not going to have all these situations, and it's not going to be every year, you know, some years you're doing things you may not need to have weed control that year, but you don't know until after that year, you know, and now and I'm not I'm not a pathologist, I'm not an enthramologist, I'm not a viticulturalist I'm a weed scientist. But you know, there's been some indications that some weeds that are growing and some of the we plant and some of that we don't are having a, you know, an increase in pathogen plant pathogens that are moved by certain insects. tikka pirate likes legumes Well, you know, especially in some of our low nitrogen situations, plants that produce their own nitrogen, like Bird Clover really tend to like that situation because they have a, they have a built in advantage by making their own nitrogen. So we can in some vineyards, we can see a high population of bird clover, which may or may not cause an increase in tikka, which could cause an increase in red blotch. So, you know, when you think of weeds just specifically for competition, like when I talked to master gardeners, I say, you know, if you're growing carrot, you know why you do weed control because you want a carrot. But when it comes to a mature, you know, a 10 year old vineyard, really hard to see that weeds are going to compete on an everyday basis like they would with an annual crop, but there are other reasons why we do it. Ease of harvest, and I talked about, you know, in talking with some pruning crews, right, you know, if you have weeds growing in when you're pruning, and I tell people, if you have an area that takes an hour for let's clean, takes a pruning crew an hour to prune, if there's a bunch of weeds that they have to move around and get around, and it takes them an hour and a half. So your labor costs have gone up 50% Yeah, these are the kinds of things that as a weed scientist, I think about I tell people I really want to know two things. And when we're when we're taping this, it's the right time of year. I only know weeds in college. Basketball. So these are the only things I really know. So, you know, and I've had other I've had, you know, some people sit down and say I should have known that you have to worry about, you know, disease pressure, and getting labor contractors. And I just think about weeds.

Craig Macmillan 20:16

And let's go back to another technology that we touched on snow plows, French plow, that's a very old technology. And, you know, we just mentioned that what a plow does is it turns the soil over, so it buries the weed plants, especially when you get into the right time, what conditions are appropriate for using a French plow? What conditions maybe it's not gonna work so great.

John Roncoroni 20:41

French plow, I mean, you know, the USDA says that, you know, doing something like that the soil is never good, and you're going to mess up the microbes, especially if you're working on that lower area. But as far as just from a weed perspective, if you're dry farming, a French blot works fantastic, right? You're not looking for, in fact, you're trying to discourage as many roots at the top as you can. So doing using a French plow when you're dry farming, it's fantastic. We don't have you know, a lot of dry farms where we are looking at trying to have more consistent harvest and looking at consistent income, where you know, dry farming were at, at the will of the of the weather, that's another talk for another day with people who are doing marketing and know viticulture are better than I do. But see, I've seen more French plows as people have gone back to mechanical in the last few years, and I have in the past think there's a lot more viable options, when you're actually looking at doing some drip irrigation, then they're just by number a lot more viable options. Just by new having new machines coming out then the French plow but I was a dry farmer, my weed control would be French plow under the vines and disk in the middle because everything's you know, maybe having a little cover crop to get more penetration. But, you know, the farther north I lived, the more water penetration I would have. So I'd get more rain.

Craig Macmillan 22:00

So let's talk about drip irrigated vineyards. And you mentioned there's a suite of technologies, some are new, some are old, what are some of those technologies that have worked well in a drip irrigated vineyard?

John Roncoroni 22:12

When I got to Napa in 2007, sustainable at that point meant post emergent only and for those kind of funny now is roundup on the right no preemergent no cultivation and we were drip irrigating, we were keeping those roots at the top so we can drip irrigate. So that's where a lot of that came from. Now, you know, using something like a blade using a little Dustin with those moving things, anything that's sort of like you don't want routine, right? Again, I don't I'm not a vitaculturalist. But roots at the very top are not great, right, you're not probably irrigating correctly, if you're getting a lot of roots at the top, but you don't want to get too deep, where you're getting some of those main roots with cultivation. You know, that's one of the reasons that we do have drip irrigation. At that level. You know, I've talked to people who weren't using cultivation and ask them why their drip irrigation lines weren't closer to the soil so they're gonna have less evaporation. One of the things that we get into with grape growing or anything is that you do things because you've always done them that way, we are cultivating that we do need to keep that drip irrigation at at a higher at a high level. But I think any of those anything that's not just completely disrupting the soil. One of the things that I would like to see with with mechanical like a blade is using some electric eye, AI technologies to get closer to the vines. But right now we have to really, you know, it's all mechanical, right? If we can have these machines down in Salinas, that are taking weeds out from in between lettuce, we don't have to be nearly that technological, to get weeds right around the vine without hurting them. And we have a little bit more leeway with the vine than we do with lettuce. Even though you lose a lettuce plant here or there. You're okay. You don't want to lose too many vines. You know, I think that that's where one of the reasons that we could use more technology. One of the things again, my doctor Moretti up at Oregon State and also lenses masky. Back in Cornell, who they were both at Davis at the same time, Lynn as a postdoc, and, and Marcelo as a as a graduate student, they're working with electrocution of weeds, I think it's what they call it. And it's not just burning them off, like you would use electric light with a flamer. It actually sends electricity down into the roots. So it's, he's working on it mostly in blueberries. But the technology I just I saw his presentation at the Western society Weed Science meeting just a couple of weeks ago in Denver. It's an interesting technology. If you're like having a transformer on the back of your tractor. It's pretty cool.

Craig Macmillan 24:35

There's a there's a lot of potential here in the future for improving what we're doing now.

John Roncoroni 24:40

Oh, yeah. And I don't know how like electric is going to fit into this. But and this is the problem. We ran into herbicides. Anytime you use one technology over and over and over and over and over, you're going to choose for weeds. If you constantly mow under the vines or anywhere, right without some soil disturbance or application of herbicide, something Like Melva, low growing weeds, they'll adapt, right nature will find a way. So the biggest thing we have to do is whatever we do just don't do it all the time. That it's the right message. One of the things that I think we want to talk about was under vine cover crop. It is something for me, I've been trying to push under vine cover cropping for so long. And the problem is, is that because the seeds are expensive, I tell people that one of the one of the plants that I pushed, just because I liked the way it worked, and what I've seen is Zorro fescue. That's a brand name, it's it's rat tail fescue, you see it growing as a weed a lot of places, one of the things I like about it is that about the time we start irrigating, it's dead, it's the nest, and you can discover you can turn it over, because once it's gone to seed, you can mow it all those things. It's a it's a self receding cover crop problem is that because the seeds are fairly expensive, we planted at about eight to 10 pounds per acre and sometimes mixed with Blendo broam, which grows a little higher and stays a little greener longer than I like, because it can be some competition for water. But that's oftentimes keeps it down. But the problem is, is that first of all, how do we get it on the vines, I find people putting it out by hand, because we haven't adapted for the cedar under the vine. Second of all, it starts to reseed itself at a fairly high rate, sometimes 50 or 100 pounds the next year and the third year. So I tell people, if you can't give me three years to make it look good, then let's not start because oftentimes, you know, we started and it looks like it's not doing a very good job the first year, and it doesn't look very good. And some people who don't ask people who make decisions about vineyards who maybe work other places, then the vineyard don't like the way it looks. Right? Right, and we move to something else and they end up spraying it