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Sustainable Winegrowing with the Vineyard Team brings you the latest in science and research for the wine industry. This on-the-go, sustainable farming educational resource provides in-depth technical information on topics like integrated pest management, fruit quality, water conservation, and nutrient management from experts like Dr. Mark Fuchs of Cornell University, Dr. Michelle Moyer of Washington State University, Cooperative Extension Specialists, veteran growers, and more. Our podcasts will help you make smarter, sustainable vineyard management decisions to increase efficiency, conserve resources, and maximize fruit quality.

Dec 1, 2022

Under vine cover crops can both improve soil health and control vine vigor. Justine Vanden Heuvel, Professor and Chair of the Horticulture Section School of Integrative Plant Science at Cornell University and Michela Centinari Associate Professor of Viticulture at the Department of Plant Science at Penn State University have trialed different cover crops to find the best plants for vineyards. By adding a cover crop under the vine, growers can impact the size of the vine by stopping vegetative growth at version. Ground cover has additional benefits on the soil including decreasing the impact of water drops, improved water infiltration, increased carbon, soil aggregate stability, and microbial activity. Listen in to learn which cover crops are best to improve the overall sustainability of a vineyard.


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Craig Macmillan  0:00 

Today our guests are Justine Vanden Houvel from Cornell University and Michela Centinari from Penn State University. And we're going to talk about some really exciting work they've been doing around the topic of under vine vegetation. Thank you both for being here.


Justine Vanden Houvel  0:14 

Thanks, Craig.


Craig Macmillan  0:16 

Tell us a little bit first of all about what under vine vegetation kind of is, to me that sounds like weeds coming from California. To me, that means weeds and it's gotta go. Your work is looking at some maybe some benefits of it and things that might help in the eastern United States at least, can you tell me kind of what the basic definitions of these things are?


Michela Centinari  0:33 

I understand why you think you know, that the under vine vegetation should go because I'm from Italy. And also we don't like to see weeds. Cover crops grown under the vines, because it's a dry, you know, hot warm climate. Is a little different for us here in the eastern United States and the Northeast US, because we have a very different weather conditions, you know, it's more or less humid, wet, and we have fertile soil. So cover crops are weeds, even weeds growing under the under the vine can actually be beneficial for the vine and for the soil. And this is because our vines can be overly vigorous, because it's, you know, it's humid is wet, and the soil is fertile. And this competition provided by the cover crops to the vine for water and nutrients can actually decrease the amount of vigor of the vines. So that is seen as a positive traits in our region, at least some of the sites in our region.


Justine Vanden Houvel  1:31 

I agree with what Michela said, and sometimes they are weeds. Sometimes they're specific species that we're we're cultivating. From a management perspective, it really doesn't make any sense in some of these eastern vineyards, not all of them, but in some of them to have this bare strip under the vines because we have to go through and hedge the top of the canopy two, three times in a growing season, we have to go through and do leaf removal once or twice in a growing season. You know, we're spending a lot of money in the industry, here on the East trying to manage the vigor of the vines. And those are Band Aid solutions, right, they don't really help fix the situation. Whereas providing that competition that Michela was referring to, can make a big difference in terms of reducing the available water and nutrients that the vine can take up.


Craig Macmillan  2:19 

What kind of species of plants are we talking about here? You know, a weed is a plant at a place. Mint is often a weed but also if I have it in a container, and it's next to my front door, and I like to have my food and it's not a weed. What kind of plants are you talking about?


Justine Vanden Houvel  2:32 

Yeah, we've been working with quite a few different plants. So some different grasses, buckwheat, chicory rosette forming turnip. We are having a problem with a lot of the brassicas though and that the groundhogs like to eat them, so we're kind of steering away from those ones a little bit. But we've worked with a wide variety of species and looked at you know, do we see a big impact on Vine size, small impact on Vine size, or no impact on Vine size, because we need to make sure we dial it in so that the grower has the amount of control of vigor that they want. We don't want to deviate the vines too greatly.


Craig Macmillan  3:10 

In terms of monitoring vigor, are you doing this from pruning weights? Are you doing this from trying to weigh green mass during the summer, this is gonna be kind of tough, because if you're hedging something two, three times, you know, how do you get a number on that? So what's your metric? How are you getting the baseline metric here?


Justine Vanden Houvel  3:28 

We mostly in my program, and Michela can comment on hers we use two methods. One is pruning weight dormant pruning weights, but the second is what we call enhance point quadrate analysis. So some of your listeners may know about point quadrate analysis which was you know, made famous by Richard Smart and sunlight into wine, my group added to sort of a calibration with a light bar in the middle of the canopy so that we can then look at actual numbers for how much light clusters are getting and how much light different leaves are are getting. And so we use those two metrics to really enhance point quadrant analysis. It's a proxy for vigor right, it doesn't measure actual growth rate, but we use that in pruning weight as our measures for this.


Michela Centinari  4:12 

Yes, yes, I mean, definitely we measure printing weight because it's something you know growers are familiar with, and it's easier to quantify. We also have been looking at changing the fruiting zone, right light exposure and canopy density. We even, and that is very labor intensive, we looked if the cover crop can reduce the length of the growing season. Basically, in our region, we see the length of vegetative growth because in our region we see the shoots keep growing after verasion on and we want them to stop earlier. So we basically assess if the cover crops can you know stop this vegetative growth around veraison that you know helps in terms of fruit ripening.


Craig Macmillan  4:59 

That's interesting. But one of the things I wanted to ask you about as part of all of this, and I think vigor may have something to do with it. The paper you're published recently had a kind of a focus on the effects of heavy precipitation. And the benefits of UVV, undermine vegetation, pardon me, jumped into lingo a little soon, and the effects of heavy rain events. That's interesting to me, because we don't have heavy rain events in California, where I'm from, and I can only imagine what it must be like. And so what are what are some of the benefits there? Oh, and actually, before we get to that, I got a question. In the east in Pennsylvania in New York, that those areas, how common is the use of under vine vegetation as opposed to a clean berm since we have an idea for how much adoption there is out there?


Justine Vanden Houvel  5:42 

That's an interesting question. And it basically depends on on how busy the growers are, how many of them have wholeheartedly adopted under vine vegetation? That's a handful in New York, it's not a lot. At this point, I'd love to see more, how many of them will absolutely let the weeds grow and then not worry about it until they get too tall? Because they know it's helping to deviate their vine? That is a fair number.


Michela Centinari  6:06 

Yeah, it's very similar here in Pennsylvania, you know, I have to say, growers are definitely interested, you know, we did lots surveys, and we see, you know, most growers want to try but then you know, they get busy. And it's hard, you know, for them to change, a management practice that is working right, you know, spray herbicide. So they need, you know, it's not always easy, right. But definitely, there is an interest, it's just not, a widely adopted practice.


Justine Vanden Houvel  6:34 

We are starting to see growers in New York purchasing the undermine mowers so that they're able to maintain and under rvine vegetation and mow it reasonably easily. And so it's been great to see people making that investment.


Craig Macmillan  6:48 

The reason I wanted to get to that was because this issue of precipitation, one of the things that I had never thought about that came up in your writing was erosion, and also so crusting and negative impacts on soil structure and aggregate formation and all that kind of stuff. Which is something yeah, very much an issue on bare ground. I had never really thought about it as an issue in let's say, July in a vineyard. Can you tell me what overall like when I've got a rainstorm like that, and I don't have under vine vegetation around what are the all the impacts that I'm looking at that I'm being affected by?


Michela Centinari  7:17 

Yeah, I mean, definitely, we see that and we, you know, I even took pictures to show growers because we do see multiple negative impacts on the on the soil under the vine. We see increase on erosion, I mean, definitely most of our vineyards you know, sloppy, you know, on a hill, so we see erosion, even if they use cover crops in the middle row still under the vine, you see this erosion, water and nutrients, you know, in soil washing out from the from the vineyard, we also, you know, showed through an experiment mostly just sean studies that there is an increase in the leaching of nutrients, whether to agrochemicals into the underground water. So definitely leaving bare soil under the vine, create, the negative impact has negative consequences on several parameters of soil health. And since you know, we want the vineyard to last 20 plus years, hopefully, you know, it's important to maintain soil health and to reduce soil degradation and definitely under ine cover crops or weeds can really help in that.


Justine Vanden Houvel  8:20 

And I'd also add that our comparison here is bare soil versus soil that's covered with vegetation, whether it's weeds or a species. Is some people will say, well, I cultivate so that's all right, but really the problem in agriculture is bare soil versus not bare soil, right? So cultivation isn't a practice that is able to help reduce a lot of these problems, like the leaching and the runoff in particular.


Michela Centinari  8:51 

And even you know, as an as important sort of, for us to increase soil carbon, and definitely soil cultivation doesn't help with that, while you know, let some type of vegetation grow under the vine can be also use as a way to accumulate carbon in the soil in addition to the other benefits that we mentioned.


Craig Macmillan  9:12 

There's also some things that you talked about that I'm super curious about, and that is other positive effects in terms of things like soil structure and soil health. What can you tell me about that? That's the cover cropping idea?


Michela Centinari  9:24 

Yes, yes.


Craig Macmillan  9:25 

So we're not simply covering the ground at this point, we're looking for other benefits.


Michela Centinari  9:29 

So definitely, overall cover crops, no, just under the vines can improve many parameters of soil health, not just you know, decrease erosion. But for example, the biomass of the covered crop can reduce the impact of the raindrops that you know can really break the soil aggregates when you live you leave a bare soil under the vine on the middle row can also improve water infiltration. So you have less you know, water runoff can also as we mentioned, improve the soil carbon or the over nutrients in the soil, which you know are all good for the long term sustainability of our vineyards.


Justine Vanden Houvel  10:06 

I'd add a couple of other soil health aspects to that is aggregate stability. So aggregate stability for soil is the ability of the basically the soil to withstand physical pressure from the outside. So usually rain in some of the studies that we've done in my program here, we saw a huge increase in aggregate stability of soil up to 80, something percent after three years, when we compared cultivation to weeds growing under the soil for those three years. We see an increase in soil respiration, which we assume means a healthier soil with more microbes. And we see an increase in microbe diversity as well. So we also did a study where we were comparing some different under vine treatments. And we saw that with each passing year, there was more diversity in the microbes when we had weeds growing under the vines than if we had bare soil under the vines. And we assume that helps in terms of nutrient turnover and, and other processes like those.


Craig Macmillan  11:10 

I'm know you'd mentioned some species at the beginning, in your work, I'm assuming this work is experimental so that you're choosing what is going on going under the vine for these different trials. Or actually, I'm assuming it's actually experimental, you must have a randomized design or some kind of replicated design of some kind. So what are the plants that you're picking to plant as that undermine vegetation?


Justine Vanden Houvel  11:30 

So my group is done lots of different iterations of these types of studies at this point, because we've done it in young vineyards and old vineyards and with hybrids or with vinifera. So they're always in replicated studies. What we basically come down to is we use usually sometimes cultivation but usually herbicide is our control for comparison, because that's what most growers here in New York are doing. And we use buckwheat as our cover crop that will usually have a very slight impact on vine vigor. So buckwheat establishes beautifully, right because it's only allopathic. So we don't tend to have a big problem with weeds, the height of it seems to be appropriate, we don't normally have to mow it, it doesn't get up into the fruiting zone kind of flowers falls over and there's not a lot of management there. And the most we've ever seen at reduced pruning weight might be by 10% or so. On the much more significant side we have chicory root. So chicory is pretty low growing, you can get a dwarf version of it. And I should mention, we normally work with annual cover crops because we hold up over the graft union to protect scion buds in the winter. Chicory is technically a biennial, but what we find is it just keeps coming back, coming back coming back. It can deviate a vine significantly. So we've used it in some of the bigger vineyards when we've wanted to really pull back on the pruning weight. Sometimes that's been up to about 30% compared to our control of herbicide, and then we found that different grasses are somewhere in the middle in terms of their impacts on vine vigor.


Michela Centinari  13:06 

Yeah, no, definitely. I mean, it's the same for us, right, we try different type of cover crops, depending on the growers, you know, what they need, what they want to achieve. In addition to what Justine mentioned, we also have been doing some work with perennial grasses, because for some growers, you know, they like, they like to plant something perennial, right. So that reduced the amount of work that they have to do, you just planted once and if you plant a species that doesn't grow too tall, you don't even have to mow sometimes the grass, so it's kind of a lower maintenance. So again, depending on what the grower needs, and what is feasible for that site, you know, we try to match the cover crop with with the site.


Craig Macmillan  13:45 

And I'm sorry, I might have missed it, what type species of perennial grasses are we talking about?


Michela Centinari  13:49 

So we try and for example, the creeping red fescue, we also try other fescue mixes mix of different fescues including like tall fescue and and we try, you know, to look for species that grow well in a kind of shaded area, because it's not in the middle row. Like it's different. You have more sunlight there. So you want something that establish quickly so the weeds don't grow overgrowth in the grass, and also something that doesn't require too much management in terms of you know, more in like Justine was talking about, you know, buckwheet, chickory, because that is not something that the grower can easily do, like in the middle row, or not every grower can easily do.


Craig Macmillan  14:28 

My next question is so how do you plant these grass seeds in the row? Grasses are tiny, they need to have a little bit of cover. It's not a planting grass is not a simple thing. Usually you have to prepare a seed bed. How do you how do you do it? I just am really curious about this.


Justine Vanden Houvel  14:46 

So that's a good question. So Michela , and I both have grad students so for years it was our grad students.


Craig Macmillan  14:54 

I was a graduate student once I see how this works. Okay,


Justine Vanden Houvel  14:58 

Bbut no knowing that the growers were never going to want to do that, I worked with Hans Walter Peterson, who is the viticulture extension specialist for the Finger Lakes here for Cornell Cooperative Extension. And he designed basically a fertilizer spreader, he did a welding design that has two shoots that go off the back to put the seed under the rows. And we can just dump the seed in that drive down the row and set the spinning rate. Sorry, I'm not a good equipment person. So I'm probably not using the right names here. We set the spinning rate for how quickly we want the seeds to come out.


Craig Macmillan  15:31 

The application rate.


Justine Vanden Houvel  15:32 

And we have that you can look it up online he has a video on YouTube, if anybody's interested in who happily shares those plans so that growers can build their own.


Craig Macmillan  15:40 

That's fantastic. That's fantastic. You said extensionist in the Finger Lakes region. And his name again was?


Justine Vanden Houvel  15:46 

Hans Walter Peterson.


Craig Macmillan  15:47 

Walter Peterson . And God bless you. Dr. Peterson.


Justine Vanden Houvel  15:50 

Yeah. And he and Alice Wise, who's our extension specialist on on Long Island for Cornell, they've done a lot of work on how do we get growers to adopt some of these practices. So Michela and I have done basically the research that informs it, but they've looked at what are some of the obstacles? And how can we overcome those so that we can get rid of bare soil in the spots where we really don't need to maintain it here?


Craig Macmillan  16:12 

Oh, that reminds me of something else. So in Finger Lakes, Pennsylvania, I don't know very well, I don't know either region really? Well, I gotta admit, is all of the water coming from summer precipitation, or is there supplemental irrigation?


Justine Vanden Houvel  16:24 

There's a handful of people with supplemental irrigation here, but it is not very common in the Finger Lakes of New York.


Michela Centinari  16:31 

Yeah, neither neither for us. Mostly, like in young vineyards.


Justine Vanden Houvel  16:35 

Yeah. I mean, we can give you an example. We got an inch and a half of rain here just yesterday. Alone. Right. We get a lot of precipitation. And in some years this year, started out dry. But then it's been raining pretty consistently for a couple of weeks. Now.


Craig Macmillan  16:52 

Pardon my presumption is, but it sounds like the team should be working on fungal diseases. That's what's going on. That's a lot of rain. That's a crop killer.


Justine Vanden Houvel  17:00 

Yeah, that's what the pathologists are working on. But we should actually mention. So there has been some good work on under vine cover crops done in Uruguay, where they looked at weather, botrytis, and I think some other fungal diseases, I'd have to refresh my memory on that, was impacted by under vine cover crops. And indeed, because of the reduced vegetation in the canopy, right, smaller leaves and just the canopy not being so thick, they did see a reduction in cluster rots as a function of under vine cover crops as well.


Craig Macmillan  17:31 

There you go. That's fantastic.


Michela Centinari  17:33 

Yeah. And that's great. Because actually, several growers here are concerned about growing under vine cover crop that will increase disease pressure, because they're afraid about you know, the humidity, increasing humidity in the under vine area. But like Justine said, We never observe or measure any negative effect of under vine cover crop on you know, increase in mold to other fungal disease. Actually, sometimes if there is an effect is a positive effect. What actually we don't know yet is, you know, if we can increase the presence of pests under the vine, right, like a course, some insects or other type of pests. We never had any issues in our vineyards, I mean, in vineyards, where we are conducting research, and that is something definitely that, you know, could potentially be a problem. We don't know yet.


Craig Macmillan  18:22 

Okay, I'm gonna ask a tough question here. That's because we've kind of ended up here. I'm a grower, I'm worried about too much impact on vigor, I'm worried about the disease, I also might very likely have a gut wrenching fear of something getting out of control, and me not being able to control it or remove it. If I changed my mind, or I don't like what's happening. How do you put that fear to rest, that I'm not going to lose control of my floor, I'm not going to lose control of my row. It's okay. But this is goes back away. So Paul Annua, for instance, was one that a friend of mine was looking at as an underground vegetation in California. And I said, Hey, why don't we just use Bermuda grass, it's summer dormant. It loves the earth, it's great. And he was like, if you try to get anybody to plant that you're gonna get killed, you're gonna get shot in the head. Like, if you go around, recommending we plat Brumida, you're gonna get killed. When I had experienced with it in a vineyard where he had escaped. I had worked with it, but here was the thing. There was no getting rid of it there that we were that was it. We were committed, there was no getting away from it. And so I can see having the same kinds of fears about a species of plants that I haven't worked with before, for instance, or what happens over years and years and years. What are you going to do to help me sleep at night?


Michela Centinari  19:28 

Wow, the tough question. No, I mean, definitely, you know, it's a tough decision and manufacturing needs to be taken into consideration. So I wouldn't just go and plant something right you need to do your research and work maybe with the extension or you know, with specialists even to make the right decision. Also, I recommend trying on in a small area of your vineyards. So no just you know, plant everywhere. If you have you know, 10 acres, or maybe try on a few vines and see how it goes right and see if you can keep it under control. If it's dry and there is too much competition for the vines, you know, maybe to be able to do a soil cultivation or kill your your cover crops, you know, plan or to head on options on what you can do to be able to manage, but definitely on choosing the right species is the first step, right.


Justine Vanden Houvel  20:15 

Yeah. And I'd add to that, you know, where I could see it being a problem is what we call resident vegetation. So keep in mind, and in a at least here, we always have a cover crop between rows, right, we usually start with some sort of an orchard mix, and it becomes whatever and we really don't care, we're not going to bother replanting that. So we have that as a little bit of protection. But when we allow weeds to grow under the trellis, and then just mow them down, I know, I've heard that there's some concerns that we might have a weed there get out of control, and then continue to propagate itself. And that is a possibility. But what we actually find is that as each year progresses, we get more and more species in that undermine part of the vineyard. Right? Often we've started in vineyards where they've sprayed a preemergent in previous years. And the first couple of years, we have like two species four species, five species, and then in a few years, we're up to 30 or 40 different species of of weeds in there. And so it does give me at least some hope that it would be very difficult for something to get completely out of control. But what we usually tell the growers here is that if you were going to spray a herbicide anyway. And now you've tried to under vine cover crop, if you don't like it, you can hopefully get rid of it. Right. But the other thing we tell them is that we probably don't need the same cover crop under vine cover crop year after year, right? Because once you, for example, devigorate the vines a little bit and get them back to a more manageable size using chicory, for example, then you want to keep them at that size. You don't want to keep dropping the pruning weight year after year. So every year there needs to be a decision about what did I think of the vine size and the canopy characteristics last year? What's the predicted weather? And what am I going to plan to maintain under the vine for this year?


Craig Macmillan  22:05 

We're getting close here to wrap it up. So there's two quick things I want to ask you what each for each of you will start with Justine, what is the one thing you would like growers to take away from your recent work on under vine vegetation?


Justine Vanden Houvel  22:16 

Bare soil is not a good idea in vineyards environmentally, really, it's quite a poor choice. And there are options for if you have small vines or or young vines or a lack of vigor, vigor. There are some potential options out there. We haven't done all of the research on this yet, but that there are options to explore.


Craig Macmillan  22:40 



Michela Centinari  22:40 

Yeah, definitely. I mean, I agree with Justine, there are options. Of course, we don't have one cover crop that can solve all the problems that definitely bare soil is no good, especially again, in our region. And our growers are also concerned about the cost of implementing under vine cover crops. And I'd say you know, for us, sometimes planting a perennial for example, grass is no more expensive. I mean, depending on depending on the year, how many times you spray herbicide and the effect of on the on the yield of the vines, but it's not necessarily more expensive than spray herbicide or sub cultivation. So hope they get cover crops a chance.


Justine Vanden Houvel  23:18 

So Craig, we've mostly been talking about work here on the East Coast where we tend to have a lot of precipitation, but we have colleagues in in other countries and other climates that are doing work on under vine cover crops as well. And there's been some great work that's been done in the south of France, in Spain and in Australia. And so while Michela and I haven't focused our research, of course on California, there are going to be some opportunities for growers in warmer climates as well.


Craig Macmillan  23:46 

And where can people find out more about you and your work Justine, go first?


Justine Vanden Houvel  23:50 

Probably the easiest spot is on the Cornell webpage, or I am on Twitter. My one social media is Twitter. And my handle is @thegrapeprof. And I tweet about research and mostly in viticulture, but a little bit of a enology as well.


Craig Macmillan  24:06 



Michela Centinari  24:07 

Yeah, I would say have a Twitter account. I'm not very active like Justine. I should. You know, I have a website if you Google actually Centinari lab, Penn State so we have you know our lab website where we post about research and also we have an extension web page prep and wind through Penn State.


Craig Macmillan  24:26 

Fantastic and for audience, that information plus links to some other things will be in the show notes. Want to thank you both for being here. I guests have been Justine Vanden Houvel and Michela Centinari. They're doing fantastic work in an area that most of us in the West Coast certainly don't know about. But I know there's important for other regions of not just the United States but the world. You guys are doing great work.


Justine Vanden Houvel  24:45 

Thanks, Craig. This was really enjoyable.


Unknown Speaker  25:07 



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