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This week’s podcast, sponsored by Montag Manufacturing, features Tony Wolf, Professor of Viticulture, Virginia Tech University. Wolf will discuss the benefits of cover crops in vineyards, the potential for yield reduction due to cover crop use, using perennials vs. annual cover crops in vineyards, and more.
The Cover Crop Strategies podcast series is brought to you by Montag Manufacturing. Montag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, Montag’s family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water. Explore new options for your production and conservation goals with your Montag dealer, visit www.Montagmfg.com or call Montag at (712) 517-2775.
The Cover Crop Strategies podcast series is brought to you by Montag Manufacturing.
Montag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, Montag’s family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water. Explore new options for your production and conservation goals with your Montag dealer, visit www.Montagmfg.com or call Montag at (712) 517-2775.
Full Transcript
Sarah Hill:
Welcome to the Cover Crop Strategies podcast. I'm Sarah Hill, associate editor. Montag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, Montag's family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water.
Sarah Hill:
Explore new options for your production and conservation goals with your Montag dealer or on the Montag Manufacturing website. Welcome to the Cover Crop Strategies podcast. I'm Sarah Hill, associate editor. Today, I'd like to introduce Tony Wolf, professor of viticulture at Virginia Tech University. Tony will be discussing using cover crops in vineyards and how that can affect soil health. Welcome to the podcast, Tony.
Tony Wolf:
Well, thank you. I appreciate the invitation to join and look forward to it. As you indicated, I'm a professor of viticulture with Virginia Tech. I've had a long tenure here in cover crops and in the broader sense, vineyard floor management is just one area of research that I've been involved with over the years.
Sarah Hill:
Fantastic. Well, to get us started, why don't you give us an overview of what type of growing conditions viticulturists have to deal with there in Virginia?
Tony Wolf:
Yeah. Great introduction, because for many of your listeners, they may not really fully appreciate the kind of environment that we grow grapes in here. When we think about the climate of Virginia, it my come as a surprise that it's a continental subtropical climate. We have a lot of rainfall typically throughout the growing season. We're not a winter dominated rainfall, Mediterranean type climate as some of your listeners on the west coast might be or would be.
Tony Wolf:
But instead, we have rainfall and occasionally very violent thunderstorms throughout the growing season. So water, although grapevines need it, water sometimes is at a surplus. We have more than what we can deal with, and therein lies one of the uses of cover crops is to help mitigate some of the issues that come with that rainfall.
Tony Wolf:
We also have a fairly warm growing season here in Virginia and elsewhere in the Mid-Atlantic region, and so collectively the abundant moisture, sometimes very fertile soils, deep soils, and the humid warm conditions that we have, are also very favorable for some of the diseases that affect grape vines. So that's an added challenge that we have with grape growing here, but our growers of course have found ways and we've researched ways of lessening some of the negative impacts of those environmental factors.
Sarah Hill:
Absolutely. Let's get to the nitty gritty here. Talk about some of the benefits that cover crops provide to vineyards. I know you mentioned dealing with excess moisture, so let's start there.
Tony Wolf:
I think it would be important too, to define what we mean by cover crops and where they're grown. We think of vineyards as having two crops essentially. Here in Virginia we grow the grapevines of course, but the other crop that we grow on a perennial basis in the vineyard are cover crops. And there are really two locations that we think about those cover crops.
Tony Wolf:
Between the rows, which is a very traditional way of managing vineyard floors here in the Mid-Atlantic region, and then under the trellis or what we might call intra row or in the row type of cover crops. These are a little less common. However, in recent years, we've seen an increased adoption of in the row cover crops as well, both perennial and annual cover crops. We'll get into some specifics with questions and answers on the nature of those cover crops in a bit.
Tony Wolf:
But in terms of overall advantages, the chief reason we use cover crops here, as I mentioned before, we do have quite a bit of rainfall that occurs here. Our average rainfall varies throughout the state, but we're talking about figures of anywhere from 38 to maybe 48 inches of rainfall per year. So it's considerable compared to some of the west coast vineyards. If we did not have cover crops in the vineyard, even between the rows we would have some real problems with soil erosion.
Tony Wolf:
Many of our vineyards are located on steep terrain or at least sloping terrain, and of course when you have rainfall hitting on bare soil, it tends to increase soil erosion and that soil moves downhill. It's a classic problem. So cover crops between the rows are our primary ways of lessening or mitigating soil erosion.
Tony Wolf:
They provide a platform for vehicular traffic or machinery in the vineyard of course. If you need to get in and spray soon after a rainfall, it's good to have a cover crop on the ground so that you don't get mired in mud. And then they're also very helpful in improving soil structure. We have some pretty heavy clay soils that occur in our vineyards here, and cover crops, particularly deeply rooted cover crops, are helpful with improving water infiltration into the soil, improving soil structure, and there are a lot of other biological soil health benefits that go along with having these cover crops in the vineyard.
Tony Wolf:
Now, as we move from the row middles into the under trellis portion of the vineyard, traditionally and historically, weed management has been very important to our vineyard management, and weeds are typically controlled under the trellis either through mechanical means such as cultivation, or through the use of herbicides, both free emergent herbicides and post emergent herbicides.
Tony Wolf:
We still do that, it's still fairly common to use either cultivation or chemical weed management tools, but one of the issues that we have with vineyards here in Virginia, most of our vineyards are grafted vineyards. We're growing [inaudible 00:06:35] for varieties that coupled with the root stocks that we use, we typically produce very large vines. These vines have high capacity for vegetation production, as well as yield production.
Tony Wolf:
So our labor management during the growing season is often tasked with having to go back in and do remedial canopy management practices because of these big grape vines. We're growing big grape vines with big grape vine canopies, and we have to do a lot of remedial labor with leaf thinning and sheath thinning. So we've been interested for some time in implementing some desirable level of competition with the vines for both water resources as well as nutrient resources, in a way of suppressing some of that vegetation.
Tony Wolf:
And that's where we found an added benefit of the in row cover crops. We could compete with the vines in a predictable fashion, and reduce some of the vigor and vine size that come with these big fines. So that's an added benefit that we've derived. It's not a free lunch. You can go overboard and these cover crops can become overly competitive if you're not careful. But finding that balance is all part of the good vineyard management that we're doing. So again, I just want to recap we have two types of vineyard cover crop.
Tony Wolf:
We have those that are between the row, very traditional. These are typically grasses, perennial, cool season grasses, and then we also have the cover crops under the trellis in some vineyards. And so we have these two special locations or areas in the vineyard that I would differentiate for your listeners.
Sarah Hill:
Fascinating. Something we see on the cash crop side of things is that sometimes cover crops can result in a slight reduction in yield. Do you see that and any negative effect of cover crops on vine capacity or yield?
Tony Wolf:
Certainly, certainly. And let's take a very abstract or radical approach to that. If you don't control weeds in the first place particularly in a young vineyard, you're going to have a negative impact on the vine, what I call capacity. The vine's ability to produce both vegetation and fruit. That's a classic situation of letting the weeds get the upper hand.
Tony Wolf:
Weeds are essentially in that case a cover crop, an undesirable cover crop, so that can happen. With the strategy though of using cover crops as a means of instilling or imparting some vigor reduction on the vine, we're really using these cover crops a little bit more aggressively in the second or third year the vineyard's establishment. So we allow the vine to get its root system developed, to get the framework of the training system in place, before we impart some of this vigor reduction on the vine.
Tony Wolf:
Now, what happens though over time is that we do see, and particularly if the nutrient management is not maintained in the vineyard, we will see that these cover crops can become overly competitive and they don't necessarily reach an equilibrium in terms of the nitrogen cycling and in particular in the vineyard soil.
Tony Wolf:
We had hoped, we had thought maybe that they would reach that point with the imparting of additional organic matter into the soil, but we have found that we do have to come back in and apply nitrogen. We had to do that before we used these cover crops more aggressively anyway. We don't necessarily use a lot of nitrogen compared to certain other crops, but we have found that particularly with the use of perennial cover crops, we do have to add nitrogen back into the system, or vine size and yields will start to go down over time.
Tony Wolf:
That may take four or five years, we may even see it earlier than that. What we have seen with our own research is that the cover crops have a range of effects on what we call the components of yield in grape vines. Those components really start at the berry level, and we see a slight reduction in average berry size where we use these cover crops. It's not very large, but when you consider the number of berries produced in an acre, it adds up.
Tony Wolf:
So cluster size or cluster weight, which is the next component then, also goes down and yield per vine also goes down. But where we've looked these aggressive use of these cover crops over a long period of time, it's not a dramatic reduction in yield. The yields may be off 15% or so compared to using an herbicide strip under the trellis, and the question I would raise with growers is that yield an acceptable level for, in our case, wine making?
Tony Wolf:
Does it translate into a higher wine quality potential, or at least a satisfactory yield to recover cost and make a profit as an independent grape grower? In many cases, our grape growers are having to reduce yields to meet winemakers' specifications anyway. So a slight reduction in yield, 15% or so, may not be a penalty that they would consider they really have to worry about.
Sarah Hill:
So you mentioned perennial cover crops, and I am curious, are perennial cover crops or annual cover crops a good choice for vineyards? And how do viticulturists determine that?
Tony Wolf:
It really depends a little bit on where your vineyard is located. Here in Virginia, we're generally not immune, but we have very low risk of winter injury to the vines. So our growers have moved away from some of the winter protection strategies that are used in colder environments, such as hilling up of the graft unions. With grafted vines, in areas that are susceptible to cold injury, part of the floor management of the vineyard is to annually come in with a plow basically, and hill a berm of soil up over the graft union of the vine in a portion of the sign variety.
Tony Wolf:
And in so doing, is providing a thermal protection or buffer if you will, from the cold temperatures. So if you had a very catastrophic cold event that killed a much of the above ground portion of the vine, you still have a portion of the vine that has been protected by soil that can be taken down in the spring, and the vines can be retrained from buds that will originate on that protected portion of the trunk.
Tony Wolf:
So we've gotten away from that. And in doing so, if you think about it, perennial means that you're not going in and planting every year or destroying the cover crop every year. You're planting in and staying there year after year. If you're hilling up and dehiling on an annual basis, you can't really use a perennial cover crop. You have to go to annual cover crops.
Tony Wolf:
So that's one big distinction between us and, say, some of the growers a little bit further north in Pennsylvania and New York state, for example. Perennial cover crops work well in our environment. Of course, that's what we use between the rows. I mentioned that before. We're using turf type fescues for the most part, but sometimes orchard grass, sometimes perennial rye, and these are often mixed, if you will.
Tony Wolf:
They're weedy in the sense that they may have quite a bit of white clover that grows concurrently with them. It's mixed in not because it was planted, but it's a pretty invasive species, and we don't really mind it being there either because it's low growing, and it does provide some nitrogen to the vineyard if it's destroyed. There's very little nitrogen we feel that comes from the plant while it's alive.
Tony Wolf:
But if it were to be cultivated in, it does release that nitrogen as many legumes do. The cover crops that are growing under the trellis for the most part where we can get away with perennial cover crops will do that as well. We use low growing perennial grasses such as creeping red fescue which does very well in our environment here in the Mid-Atlantic. We're in kind of a transition zone between cool season grasses and warm season grasses.
Tony Wolf:
We do have some interest in warm season grasses such as Bermuda grass, which is a very vigorous and very aggressive grass. But we're kind of in a transition zone. We're not sure that that can maintain its viability from year to year, particularly here in Northern Virginia. Zoysia grass, which tends to be very expensive. It's used in turf applications, but not necessarily in vineyards.
Tony Wolf:
The other interest when growers ask about cover crops, they often say, "Well, what about something that will benefit pollinators?" Whether they'd be honeybees or other insects that might be beneficial in the vineyard. It sounds like a great idea, but the caveat there is that we have an insect pest here in the east and it's move further west called Japanese beetle. It's been around for a long time.
Tony Wolf:
It just simply devours the foliage of grapevines. It's not a difficult pest to control with insecticides. You do have to spray it a lot. But the problem with using pollinating attractive vegetation in the vineyard is that even with white clover, I feel we're setting the stage or the table, if you will, for these pollinators to come in. And then if we have to hit the grape vines with an insecticide for Japanese beetle for example, it can be very destructive to those pollinators.
Tony Wolf:
I've argued that if we're going to go with cover crops under the trellis and even between the rows, they should be non flowering, really just so that we're not attracting pollinators into the vineyard where they could be harmed by our insecticide sprays. If you want to go with the route of pollinating, attractive cover crops or vegetation, by all means do it. But do it outside of the vineyard where you don't necessarily have to spray it.
Tony Wolf:
Maybe do it around the edge of the vineyard where you can attract these beneficial insects in, but don't have to hit it with an insecticide.
Sarah Hill:
We'll be right back to the podcast, but first, I want to thank our sponsor. Montag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, Montag's family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water.
Sarah Hill:
Explore new options for your production and conservation goals with your Montag dealer or on the Montag Manufacturing website. And now, back to the podcast. All right. Seeding covers in between the vines or under the trellises probably is rather challenging. What seeding methods are best for viticulturists to use when adding cover crops in the vineyard?
Tony Wolf:
Seeding or sewing, its been one of the hardships really. Between the rows it's not too big of a problem. You can either broadcast seed, or you can drill seed into the ground without any problem. Under the trellis, you have the practical limitation though of having trumps and trellis post in the way. And we don't have availability of drills, very small drills.
Tony Wolf:
We really need something on the order of about an 18 inch wide drill that would be able to go down one side of the row and up the other side without hitting the trunks to drill seed into the ground. That would be a very precise way of putting the seed down. So rather than going that route, we've tried different things. And when I say we, some of this has been work that research colleagues on Long Island, for example, with Cornell have done some work in this regard.
Tony Wolf:
They've modified broadcast spreaders to discharge seed in a defined band to the side of the broadcaster so that you're only really putting the seed down under the trellis. That still leaves the need though to go back in and either lightly cultivate it into the ground, or somehow get it covered with something that will help with germination and the early survival of the seed. So it's been a challenge.
Tony Wolf:
I don't have a good answer to that question of what's the best way to do it. In very small vineyards, I've seen people resort to broadcasting with a chest mounted broadcaster, one of these things that you wear over like a nap sack, and you can spread the seed that way. And if you're dealing with a very small vineyard, five acres or less, it takes a little while, but it can be done that way.
Tony Wolf:
And then going back in and either putting a light dusting of mulch on top of it, or straw. Something that would just give a little bit of cover for those seeds to get going. And most of this seed sewing again, if we're talking about perennial grasses, we're doing this late in the summer. As late as September, now even into early October. So you have a fairly wide window to do it, but getting the seed bed right, that is getting a clean seed under the trellis, being able to get the seed down in contact with the soil and then providing some cover to it, has admittedly been one of the limitations with getting that cover crop growing under the trellis.
Tony Wolf:
And I'll use the opportunity here with that qualification or that statement to say that this is one of the reasons why a lot of growers just say, "No, it's too much effort to try to get the cover crop growing under the vines and then keeping it mowed or occasionally mowing it is much easier." And I'll be the first to admit, it's much easier to use herbicides and even cultivation under the trellis, and I get that. I understand it.
Tony Wolf:
But you don't get that benefit of reduced vine size with those strategies.
Sarah Hill:
So you mentioned using herbicides. Is there any concern about using herbicides and the potential of them harming the vines or the fruit?
Tony Wolf:
Well, two answers for that. Let me get the first. I think if you follow the instructions, the label, use the herbicides in the way they were intended to be used, no. I think you have very little chance of harming the vines. That said, there are many people that would like to reduce the synthetic inputs into the vineyard one way or the other.
Tony Wolf:
In our environment where fungal diseases in particular are such a challenge, we're not really making a lot of headway on reducing our fungicide input in the vineyard, and now we have invasive pests like spot and lantern fly that we're going to have to deal with, and that includes using more insecticides until we can come up with biological controls. So the one area of pesticide usage that we at least have some latitude in reducing our inputs would be in the area of herbicides.
Tony Wolf:
Herbicides come in different shapes and forms of course. We have the pre emergent herbicides, we have post emergent herbicides. Many vineyards have gotten away particularly where they're using these perennial cover crops. They have been able to get away from using pre emergent herbicides for the most part. In our research vineyard, we still use a combination of cover crops under the trellis and herbicides.
Tony Wolf:
We use the herbicides selectively to keep what I call a halo of open area immediately around the trunks of the vines. We also find the need occasionally to do some spot treatment of what I would call more noxious or aggressive weeds, particularly woody weeds such as poison Ivy or Virginia creeper. These are climbing Leanna type plants like grapevine, and if they're not controlled, if they get out of hand, they can really take over the canopy of the grape vine during the course of the growing season.
Tony Wolf:
So we do some spot treatment, particularly with use of glyphosate or another contact herbicide perhaps, or another systemic herbicide to spot treat some of these more noxious weeds in the vineyards.
Sarah Hill:
All right. So let's shift gears here and talk a little bit about soil health in the vineyard. How do cover crops help with maintaining those nutrient levels in the soil? You've kind of mentioned that a little bit here and there, but I'd like to dig into that a little bit more.
Tony Wolf:
There's a couple ways that the cover crops can help. If we think about soil erosion for one, when we do have soil erosion, we're losing some of the most fertile soil, the top soil from the vineyard first. That's the first to go. So anything that's going to help with reducing erosion is going to keep more of the nutrients in place within the vineyard.
Tony Wolf:
The other thing that cover crops do is they have a tendency to sequester some of the nutrients in the soil or in the vineyard system. They do take up nitrogen, they will utilize nitrogen, and they're competing with vines for nitrogen. Nitrogen of course in most cases, it's going to be our chief limiting nutrient in most vineyards here, meaning it's the nutrient that we're going to have to apply on an annual basis or maybe every other year basis in order to maintain vine size.
Tony Wolf:
It does sequester it in the sense that if you don't take the sword that is you don't cut the vegetation and take it out of the vineyard, that nitrogen is recycled within the vineyard and sequestered also in the form of organic matter. The thatch, the other inner materials that comprise that first inch or two of the soil profile, it's a nice reservoir for some of those nutrients in the vineyard.
Tony Wolf:
Same way with phosphorus, potassium, magnesium, some of the other nutrients. Most of the other nutrients we're not quite as concerned about though because of their attraction to soil colloids and their ability to be retained by a mineral soil that might have even very low, organic matter levels in it. So there's the recycling of nutrients, there are the spinoff benefits in terms of soil organisms that are enhanced with a living cover crop on the vineyard floor, the water infiltration.
Tony Wolf:
I talked about the negative impacts of water in our environment, but again, grapevines do need water and we do have drought periods here in the summer occasionally. So having the ability of a vineyard soil to allow water to move into it is also important for vine welfare. Soil health wise, you can think of the macro organisms that utilize the soil. Earthworms for example. If the structure is good, if soil organic matter levels are good, we do see more earthworm activity.
Tony Wolf:
I think earthworms are a great proxy for soil health because we can see them, we can count them if we want and give a good indication of the overall health of the soil. I would be remiss if I said that all soil organisms are beneficial. We do see situations where cover crops on the vineyard floor do raise the levels of rodents in the vineyard. We have fowls this part of the world, pine fowls and meadow voles, and we do see greater in cases.
Tony Wolf:
We do see greater abundance of those voles on the vineyard floor where cover crops are used extensively compared to where we have herbicide strips or no cover crops between the rows, which is a very rare situation anymore. Do these mice, I'll use the term very generally there, they're technically voles, but do these voles harm grape vines? We've not seen evidence of that in our own vineyards here, but occasionally I will hear growers tell me that they have seen problems.
Tony Wolf:
And I have seen problems myself in recently planted vineyards where young grape vines do appear to have been affected by pine voles, which are feeding down lower in the soil profile. So that's just one of those things that need to be taken into consideration. There may be situations where those rodents do become a problem. And again, just for the benefit of your listeners, I want to emphasize I'm only really talking about the Mid-Atlantic region here.
Tony Wolf:
If your audience is on the west coast, pocket gophers and other larger rodents may be a bigger problem, and maybe even a greater problem where cover crops are used more extensively. So I'm really confining my comments to here in Virginia and elsewhere in the Mid-Atlantic.
Sarah Hill:
All right. Well, where can our listeners go for more information about cover crops and soil health in vineyards?
Tony Wolf:
We have a recent publication. It's freely available online. This is really a culmination of a lot of our research over the years as well as many other researchers efforts. If one would simply search for floor management strategies for Virginia vineyards, they'll find that at publication. It's a Virginia Cooperative Extension publication. There is a lot. As I look through available online materials, there's quite a bit of information out there on vineyard floor management and the use of different strategies for integrating cover crops into a vineyard situation.
Tony Wolf:
Whether you're in a cold environment or whether you're in a more tolerable environment like we are where you can maintain perennial cover crops. But I would call attention to our publication. It's a fairly recent publication, fairly extensive in terms of what some of the questions are that come up. We have part of the publication that's devoted to questions and answers on issues such as soil health and alternative means of controlling weeds under the canopy.
Tony Wolf:
There's lots of different ways of doing that, Sarah. So that would be my first go to publication. It's free.
Sarah Hill:
Great. Well, that's all the time we have for today. Thanks so much for joining us, Tony.
Tony Wolf:
And thank you again for the invitation. It's been my pleasure.
Sarah Hill:
For more information about all things cover crops, visit us online @covercropstrategies.com. Once again, I want to thank our sponsor. Montag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, Montag's family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water.
Sarah Hill:
Explore new options for your production and conservation goals with your Montag dealer or on the Montag Manufacturing website. For more information about all things cover crops, visit us online @covercropstrategies.com.
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