Rick Dunst, Viticulturist, Double A Vineyards, Inc.

Most grape growers recognize the need to determine the nutritional status of their soil prior to planting, but it is also important to monitor the nutritional status of the vineyard on a regular basis once it is bearing fruit. Ideally, soil and petiole testing are used together to monitor the nutritional status of the vineyard in order to anticipate deficiencies and correct them before they affect vine growth, fruit set, and fruit and wine quality, but testing is also often used to confirm deficiencies suspected after the development of symptoms on leaves or fruit clusters. Soil and petiole tests should be taken every three years or so in order to gauge vineyard nutrient levels to optimize vineyard nutrient status or to correct deficiencies with appropriate supplemental fertilizer applications.

Double A Vineyards offers nutrient analysis through a reputable laboratory and provides interpretation and recommendations appropriate for native, hybrid, and vinifera vineyards. You can order your nutrient testing package here:

Soil Nutrient Testing Package

Plant Nutrient Analyses- Petiole Package

Soil and Plant Nutrient Analyses Combo Package

Once you receive your sample kit, collect and dry the sample and mail it to the lab. Results are sent to our viticulturist who will forward them to you along with recommendations appropriate to the cultivar being grown.

Soil tests can be collected any time of the year it is convenient, but researchers have identified two optimal growth stages for collecting and analyzing petiole samples to monitor vine nutrient status: during bloom, and in the period between veraison (initial fruit softening and/or coloring at approximately 7° brix) and harvest. Bloom petiole sampling is preferable if poor fruit set has been a problem, especially in identifying micronutrient deficiencies involving boron and zinc. Many growers find themselves overwhelmed with vineyard tasks during bloom, and petiole samples taken after veraison but before harvest can be useful to determine the status of most nutrient levels in the vineyard. Deficiencies of key nutrients such as potassium and magnesium are readily identified from grapevine petiole samples taken either at bloom or after veraison and can be used to adjust fertilization practices prior to the next growing season.

How to Collect Samples
As mentioned, soil samples can be collected any time of the year, but it is most useful for the person making the interpretations to have access to both soil and petiole data. Collect soil from several locations in a vineyard block with uniform soil. If there is more than one soil type in a vineyard block, sample each soil type separately so they can be treated differently, if necessary. Each sample should consist of at least 15 sub samples to a depth of 8”. A soil core sampler or small auger (ca. 1” diameter) can be used. Air dry the sample, mix it up, fill the sample bag provided with the kit, and mail to the lab for analysis.

Petiole samples can be collected from bearing vines at either bloom, or between veraison and harvest. The petiole is the leaf stem between the green shoot and the leaf blade. Samples should be collected from fruit-bearing shoots and should consist of 60-100 petioles. If you collect samples during bloom, collect them from the fruiting zone (leaves opposite blooming clusters). If you collect samples prior to harvest, collect the petioles from the most recently matured leaf (RML) on fruit-bearing shoots. Start at the shoot tip and work back to the first full-sized leaf which is the RML, usually about five to seven leaves back from the shoot tip. On some varieties (like Concord), this is the uppermost leaf on the shoot that shows some browning on the bottom side of the leaf. On VSP-trained vines with summer shoot hedging, sample from the upper part of the canopy a few leaves below where the shoot has been tipped. Once you collect the petioles, wash them in a solution of a drop of dish detergent per gallon or more of water, triple rinse with clean water, air-dry, and send to the lab for analysis. Sample each variety/rootstock combination separately, and take separate samples from areas of the vineyard that appear to have nutrition-related problems such as weak growth, poor fruit set, or leaf deficiency symptoms.

Rick Dunst, Viticulturist, Double A Vineyards, Inc. 

When trouble-shooting the cause of poor growth in vineyards (especially newly-planted ones) competition from weeds is one of the first things to consider. In my experience, new growers often underestimate the competitive effects of weeds in the vineyard. This article will summarize some of the concepts of managing weeds and cover crops as well as the tools used to accomplish good weed control in vineyards.

How Competitive are Weeds and Cover Crops in Vineyards?

During my career at Cornell University’s Vineyard Research Lab in Fredonia, NY, I had the opportunity to collaborate with several excellent researchers who helped me understand the concepts of weed competition in vineyards and how to manage it. Those researchers include the late Professor Emeritus Dr. Bob Pool and Professor Emeritus Dr. Alan Lakso from the New York State Agricultural Experiment Station in Geneva, NY, and viticulturist Alice Wise and weed scientist Dr. Andy Senesac who work at the Long Island Horticultural Research and Extension Lab in Riverhead, NY. The information presented in this article is based largely on their research studies and only skims the surface of our understanding of the topics, so I have listed a few references at the conclusion of this article for those of you who might be interested in more detail.

Research at the Fredonia Lab was primarily with own-rooted Concord, a relatively shallow-rooted grapevine. Studies showed that:

• Competition from weed or cover crop growth has a substantial effect on vine growth, and fruit yield and quality.

• Minimizing weed competition under the vines is particularly critical on newly-planted vines.

• Organic mulches can increase soil organic matter, conserve soil moisture, suppress weed growth, and lead to increased vine size. They can have a substantial effect on vine mineral nutrition and can result in higher potassium and lower magnesium status in grapevines.

• Actively growing cover crops, including legumes, between bloom and veraison can reduce vine size and fruit yield.

• Vine size and fruit yield increase proportionally to the width of the weed-free band under the vines. In one study in a mature Concord vineyard, vine growth was increased by over 300% when the entire vineyard floor was managed to exclude weed and cover crop growth, as compared with vines grown in solid sod cover, and irrigation could only minimally overcome the competitive effect of the sod.

• Mowing a competitive cover crop such as orchard grass has only a very limited and temporary effect on reducing the competitive effect of the sod.

Concord growers typically aim to grow large crops that meet processor quality standards. Conversely, premium vinifera growers often aim for low to moderate yields in order to produce high value fruit and wine. Where high vigor varieties or rootstocks are used, vine growth can often become excessive. In the arid regions of the western United States, regulated deficit irrigation practices are often used that create moderate water deficits. These deficits can lead to improved fruit quality, especially in red cultivars. Alice Wise, Cornell viticulturist on Long Island, NY, reports that several commercial growers are successfully reducing herbicide inputs by using ground covers or mowing weeds under the vines in mature vineyards. Excessive vine growth can be tamed to some extent where vine vigor is high due to variety, heavy soil, and during heavy rainy periods. In her experience, this practice can be risky on young vines, in vineyards with light sandy soil, and during extended summer droughts, especially where supplemental irrigation is not available.

Weed Management in Vineyards

It is clear that plant growth (weeds or cover crops) under the trellis can compete excessively with grapevines for water and nutrients, limiting vine growth and fruit yield. Vineyards are primarily a hillside crop, since good air drainage and movement are needed to minimize the risk of cold damage and the development of fungal diseases. On the other hand, large areas of bare soil (especially cultivated soil) are prone to soil erosion during episodes of heavy rainfall. In most commercial vineyards in the Eastern United States, a balance between excessive weed competition and minimizing the risk of erosion is struck by maintaining a relatively weed-free band underneath the vines while maintaining green cover crops in the row middles. Typically, about one-third of the vineyard soil is maintained relatively weed-free during the summer. There are several methods to accomplish this, some more practical in smaller vineyards than in larger ones:

• Synthetic mulches, such as plastic or geotextile, can be effective. Drawbacks include expense of the product and/or installation, and keeping the mulch in place when the wind is blowing and from equipment or foot traffic in the vineyard.

• Organic mulches need to be applied several inches deep in order to be effective in smothering weed growth. Concerns include expense, introduction of weed seed from the use of hay, creation of habitat favorable for rodents and cutworm, and the risk of nitrogen imbalances in the vines as the organic matter decomposes.

• Cultivating by hand as the sole means of weed control is only practical for very small vineyards. There are some effective tools for mechanical cultivation, but multiple passes are needed to maintain good weed control and it is difficult to eliminate weed growth at the base of the vines.

• Due to the limitations and expense of these practices, chemical weed control is the most common means of weed control in commercial vineyards. Pre-emergence herbicides kill weed seedlings as they germinate. Options include Tuscany, Diuron (liquid), Diuron (dry flowable), Prowl, and Surflan. Often, two pre-emergence herbicides are tank-mixed to increase the spectrum of weeds controlled. They are also often mixed with post-emergence herbicides to kill weeds that have already emerged, in addition to providing residual control. Two or more applications of post-emergence herbicides only can also provide effective weed control in vineyards, but options are limited. Glyphosate (available in 1 gallon and 2.5 gallon containers) is a systemic herbicide that (when applied at the proper time, depending on the weed species) kills the entire weed including the roots. Glyphosate also can cause damage to grapevines if grape leaves are contacted, and the risk of damage increases as the season progresses. Forfeit is a contact “burndown” herbicide that is also registered for use in grapes, and only kills contacted tissue with no risk of translocation to other parts of the vine. Specific information on the use of herbicides in vineyards can be found here, in University pest management guidelines, and on product labels.

Weed Control in Newly-Planted Vineyards

As previously mentioned, weeds can be very competitive with newly-planted vines, to the extent that vine growth and yield can be severely compromised. Herbicide options for newly-planted vineyards include Surflan and Prowl. Glyphosate and Forfeit can be used around young vines, but again, glyphosate contact with grape leaves needs to be avoided. The use of plastic grow tubes on newly-planted vines allows multiple applications of glyphosate during the first growing season by protecting the vines from herbicide contact while minimizing weed competition during establishment of the vineyard.

References:

https://flgp.cce.cornell.edu/timeline.php?id=2

https://ecommons.cornell.edu/bitstream/handle/1813/42888/2016-org-grapes-NYSIPM.pdf?sequence=4&isAllowed=y

https://blogs.cornell.edu/nnygrapeupdate/2014/05/14/under-trellis-management-in-vineyards-part-1/

Researchers at land grant institutions in many states have conducted exhaustive studies on the cold hardiness of grapevines, the weather conditions that cause winter injury, the anatomy of freeze injury to grapevine tissue, managing vines and vineyards to minimize winter injury, and how to deal with injury once it occurs. Some of this research is the basis for this article, but it is only the “tip of the iceberg” (pun intended) about what we know about grapevine winter hardiness. This article will focus on assessing cold damage to vines, and what to do once it has occurred.

ASSESSING COLD DAMAGE TO GRAPEVINES

During the past week or so, we have been assessing the amount of bud damage in several cultivars that we propagate in our nursery. This is an important task for us, because significant bud damage will result in reduced stand counts in our nursery the following year (hence, our strategy is to collect as much brush from our budwood blocks early in the winter before bud damage is likely to occur, or to propagate additional material if cold damage has already occurred). Assessing bud damage is also an important task in production vineyards because a reduction in live buds will likely result in reduced crop potential the following year unless adjustments are made in pruning. Thus far we have not assessed bud damage in all our varieties, but the amount of damage detected follows expected patterns. We have seen minimal bud injury (about 10% dead primary buds) in native varieties such as Concord and Niagara, and a range of injury (25-60% dead primary buds) in hybrid cultivars such as Seyval, Vidal, Chambourcin, Traminette, Vignoles and Cayuga White. Limited assessment of vinifera indicates substantial bud injury, approaching 100% dead primary buds in some varieties and locations. There is a lot of information available about bud damage from Extension programs in many states, but assessing the damage in your own vineyards is the best way to determine how to proceed in terms of your own vineyard management strategy. Winter injury is affected by many factors including temperature, the duration of cold temperatures, the inherent hardiness of specific cultivars, and the health of the vines going into dormancy.

Assessing bud damage is a fairly simple task. Collect about 50 to 100 buds from each vineyard block you would like to evaluate. These buds should be representative of the buds you would retain when pruning – in other words, if you typically prune to short canes that are 5-6 buds long, collect 10 or 20 representative canes. If temperatures have remained below freezing since the cold event that you are concerned about, place the canes in a warm location for a day or two so that freeze-damaged buds will thaw and begin to desiccate. Hold the cane with the basal end towards you, and cut through the top of the bud at its midpoint (see the photo included with this article). Use a single edge razor blade or utility knife with a sharp edge. You can start by cutting off the top of the bud, and then make a series of deeper cuts until you identify the location of the best cut to determine any bud injury. The cross-section of bud will either be green, meaning the bud is alive, or there will be a brown to black appearance indicating injury. Grape buds are compound buds with primary, secondary, and tertiary buds. If the primary bud is dead but the secondary bud is alive, the secondary bud has the potential to produce a partial crop. If only the tertiary bud is alive, that bud has no crop potential but can produce some leaf area to keep the vine in survival mode. Photos of different levels of bud damage can be found at:

http://www.extension.org/pages/63372/cold-injury-in-grapevines#.Utg1Qod3vIV

ADJUSTING PRUNING PRACTICES AFTER INJURY

Assuming vines have not yet been pruned, the pruning level can be adjusted once the severity of bud damage has been determined. If 90% of the buds are alive, little or no adjustment to your normal pruning practice is necessary. If only 50% of buds remain, then retain twice the number of buds when pruning as you would had little or no injury occurred. Once bud loss approaches 75%, the best strategy is to delay pruning until shoot growth starts in the spring, or double prune by retaining all viable wood within the vine’s space while dormant and removing additional unneeded wood in the spring. Keep in mind that increased labor inputs are going to be needed to perform these tasks.

Freeze injury to canes and trunks can also occur and is more difficult to evaluate than bud injury. Injury to the phloem and to the vascular cambium will cause discoloration underneath the bark; depending on its severity, the trunks and canes may or may not be able to recover. Trunk injury is often confirmed when vine growth resumes in the spring and sucker growth is more vigorous and healthy than growth originating from the top of the vine. Crown gall may form on surviving trunks, these can be removed in the subsequent dormant season. Buds may push in the spring but shoots can collapse later in the growing season if injury is severe, or trunks can split and produce no growth. In cases of severe trunk injury, vines may push new sucker growth that can be trained to develop new trunks, so that only one crop is lost. In the worst-case scenario where temperatures were low enough and graft unions were not protected with soil or snow cover, vines and entire vineyards can be lost. If trunk damage is suspected, follow the strategy as described above for vines with bud loss approaching 75% – delay pruning until buds push in the spring, or retain extra canes and trunks during initial pruning, removing only growth that would be pruned off regardless of injury, and remove any unneeded growth once buds push in the spring and an accurate assessment of injury can be made.

Additional information about identifying and managing cold injury to grapevines can be found in the resources listed below.

http://www.extension.org/pages/63372/cold-injury-in-grapevines#.Utl8AYco7IV

http://www.hort.cornell.edu/goffinet/Anatomy_of_Winter_Injury_hi_res.pdf

https://doubleavineyards.com/books-gifts/winter-injury-to-grapevines-and-methods-of-protection

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

After nearly twelve months of taking care of your vineyards, the last decision you make can be the most agonizing and difficult– when is it time to harvest the fruit?  As grapes mature, they develop aromas and flavors, and the chemical composition of the fruit changes.  Knowing when those factors have reached optimum levels is both an art and a science, and the answer can be different for each variety you grow.

Let’s discuss the science first.  As fruit matures, several indicators of ripeness can be measured.  The most obvious is the sugar content of the fruit, measured as percent sugar or soluble solids and referred to as degrees brix.  A relatively inexpensive refractometer can be used to measure brix in representative fruit samples or in the must.  Juice with 21°-22° brix, if fermented dry, will yield a wine with typical alcohol content of about 12%.  Many American grape varieties  such as Concord, Niagara, and many more, are best harvested long before the fruit achieves anywhere near 22° brix to avoid the development of pronounced “foxy” flavors that most people consider undesirable.  In this case, fruit can be harvested at less than 22° brix and chapitalized by adding sugar to reach the desired alcohol content.  The variety Edelweiss is often harvested at 15°- 16° brix, and Cayuga White at 15° – 18° brix, even though the fruit will continue to gain sugar beyond that point.   On the other hand, many vinifera and hybrid varieties continue to develop better flavors and aromas as they mature, and should be left to hang much longer.  Red varieties will also develop more intense color and softer, more mature tannins.

Titratable acidity and pH are two other common measurements of fruit maturity.  High acid, low pH fruit can make wines that are tart and acidic, while low acid, high pH fruit can make wines that are flat or flabby.  High pH fruit (over pH 3.5 or so) can make wines that are biologically unstable and may be prone to oxidation.  PH and acidity are determined with a pH meter, but obviously every home winemaker will not own one.  If you are working with a winery, the winemaker will likely want to work with you in collecting samples and in determining the pH and acidity of the fruit to assist in determining when the fruit will be harvested.

As opposed to the technical measures of fruit maturity, observations in the vineyard can be just as important in determining optimum quality.  For many varieties, the beginning of berry dehydration can indicate that harvest is near.  Flavor profiles change as the fruit matures.  In some cases, flavors keep developing long into the season, and fruit is left to hang as long as possible until cold weather,  animal damage, brittle cluster stems, or berry splitting dictates the time of harvest.  However, in other cases, flavors “peak” and further maturity is undesirable.  Native American varieties in particular can begin to develop undesirable flavors.  Varieties with muscat parentage tend to reach a peak of desirable flavors which then decrease with further maturity.  Frequent sampling and tasting in the vineyard (and experience) can help you recognize the best time to harvest each of the varieties you grow in order to achieve optimum wine quality.

For a more complete discussion of this topic, and additional references,  consult  “Wine Grape Quality: When is it Time to Pick” by W. Gill Giese in Wine Grape Production Guide for Eastern North America, edited by Tony Wolfe, a must-read book for anyone serious about growing grapes and making fine wine.

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

Choosing an appropriate training system for your vineyard is one of the most important decisions you will make; that decision will affect potential productivity and profitability for the life of the vineyard. The most appropriate training system for your vineyard is based primarily on growth habit and the need for optimum fruit exposure, and is affected by vine vigor and winter hardiness. Our Marketing Specialist, Danielle Huber, has published a new set of diagrams on our website depicting the establishment of Top Wire Cordon (TWC), Vertical Shoot Positioned (VSP), and Mid Wire Cordon (MWC).  This article will discuss the critical steps in vineyard establishment for these training systems.

Top Wire Cordon is used primarily for downward-growing (procumbent) cultivars such as many native Vitis Labruscana varieties. It can also be appropriate for some more upright-growing cultivars such as many French-American hybrid varieties, especially those with hardy trunks and fruit that does not need optimum fruit exposure in order to produce high quality fruit and wine. As compared with VSP training, TWC training is much more efficient as it requires much less hand labor and fewer cultural manipulations. TWC training employs a single fruiting wire at 5’ to (preferably) 6’ above ground level, on which a semi-permanent cordon is trained, and often a lower wire at about 30” above ground which is used for training purposes and to establish a straight trunk. If desired, a 7’ long bamboo stake, or equivalent, can be used as a substitute for the lower wire.

Vertical Shoot Positioned (VSP) training is used primarily for upright-growing cultivars, especially those that benefit from improved exposure to sunlight that can increase potential wine quality and minimize summer fruit rots. As compared with Top Wire Cordon training, VSP is much more labor-intensive due to the need for summer shoot positioning, leaf removal, and summer (top) hedging. VSP training employs a fruiting wire at 30-36”, and usually three sets of catch wires at 10-12” intervals above the fruiting wire.

Mid Wire Cordon (MWC) training is used where neither Top Wire Cordon (TWC) nor Vertical Shoot Positioned (VSP) training is appropriate for the cultivar being grown. Examples include cultivars with upright shoot growth that do not require maximum sunlight exposure of the fruiting zone (i.e., cultivars that have relatively disease-resistant fruit that does not necessarily benefit from increased exposure to sunlight), and also cultivars with weak trunk growth due to inherent lack of vigor or susceptibility to winter injury. MWC training may be appropriate where training to TWC is difficult due to the difficulty in establishing permanent trunks, and where economics do not justify the increased labor inputs associated with VSP training. MWC training employs a fruiting wire at 36-48”, with (generally) one set of catch wires at least 12” above the fruiting wire.

Establishment Practices During Year 1.

Establishment practices (other than trellis construction) are similar regardless of the training system employed. At planting, one or two buds are retained near the graft union on grafted vines, or near the crown of the vine on own-rooted vines. Support is usually provided with a bamboo stake or other support. For grafted vines, the graft union should be planted above the ground so the scion variety does not produce roots. Where winter graft union protection is needed in order to prevent winter injury, it is critical that the graft union be planted close to the ground (1-2” above final ground level) so that graft unions can be covered with soil or other insulating material during the winter months. Some viticulturists promote leaving more than a few shoots in the first growing season in order to maximize vine leaf area and root production, which may be a viable option, especially in warmer climates. The method of pruning to only a few shoots promotes the establishment of one or two strong canes that can be used to train the initial structure of the vine. If grow tubes are used during the establishment year, a single shoot will tend to predominate.

Practices During Year 2.

The primary goals in the second growing season are to begin to establish the semi-permanent structure of the vines, and to fill as much of the available trellis space as possible with functional leaf area in order to develop a strong root system that will be able to support a crop in future years. Regardless of training system, a single strong cane is retained from the previous year’s growth and secured to the fruiting wire, if possible. For TWC, if growth does not reach the top wire, it can be secured to the lower wire. For all training systems, a second trunk can be started by leaving a short spur at the base of the vine, just above the graft union on grafted vines, or just above ground level on own-rooted vines. Shoots often emerge from buds just above the graft union or from ground level or below on own-rooted vines, one of these may also be used to establish a second trunk. In Year Two, crop should be limited by cluster thinning or defruiting in order to encourage vegetative growth. In northern climates, second year vines are generally defruited. In southern climates or where first year vine growth was vigorous, it may be appropriate to leave a small crop, but not so much as to interfere with the development of a healthy vine that is capable of carrying a substantial crop in the third growing season.

Practices During Year 3.

The primary goals in the third growing season are to complete (or nearly so) the semi-permanent structure of the vines, and to produce sufficient leaf area in order to ripen at least a partial crop this year, and a full crop in Year 4. Third year vines should yield between one-half and a full crop, depending on the amount of trellis fill achieved. Vines that produce a full canopy of healthy leaves can be fully cropped (as appropriate for the variety and desired wine quality attributes), while weaker vines may require some fruit removal by cluster thinning so that vines are not over-cropped.

TWC:
A single cane can be pruned and trained in each direction from the head of the vine (left side of the diagram), and cordon establishment can be initiated by retaining spurs on second year wood (right side of the diagram) . Spurs should be spaced about 6” apart. For highly fruitful varieties such as most French-American hybrids, spurs can be pruned to two to three buds. For Vitis labruscana species such as ‘Concord’ where basal buds (nodes one to three on one year canes) tend to be less fruitful, vines can be short cane (long spur) pruned to five to eight buds. Shoots emerging below the top wire are removed unless they are needed for leaf area needed to develop the vine’s reserves – generally speaking, a minimum of three shoots per foot of row should be retained. As shoot growth progresses during the season, shoot positioning is generally not needed but vigorous shoots that grow over neighboring vines should be positioned downward so as not to interfere with sunlight exposure of the neighboring vine.

VSP:
A single cane can be pruned and trained in each direction from the head of the vine for cane-pruned systems (right side of diagram), or, spur-pruned cordons can be retained for spur-pruned systems (left side of diagram) . In either case, three to five buds are retained per foot of row (for example, 18 to 30 buds are retained on vines spaced six feet apart within the row). Where possible, shoots emerging from cane growth below the fruiting wire should be removed to avoid overcrowding and shading at the head of the vine, but on cane-pruned systems, one or two shoots should be retained below the fruiting wire as potential renewal canes for the subsequent year’s growth. During the growing season, shoots are manually “tucked” or shoot positioned between the sets of catch wires. Shoots that emerge through the top set of catch wires are summer pruned to encourage upright growth and minimize shading of the fruiting zone. Summer leaf pulling in the fruit zone is often performed to increase sunlight exposure of fruit to increase potential wine quality (especially for red varieties) and decrease the risk of summer fruit rots.

MWC:
Mid wire cordon training can be used where neither TWC nor VSP are appropriate, as described above. Cordons are established in similar manner as TWC. During the growing season, shoots are allowed to attach to the upper wire(s) or grow through the sets of catch wires, and additional shoot positioning can be attained by manually tucking shoots between the sets of catch wires. Shoots that emerge through the top set of catch wires are allowed to sprawl, generally without using any summer pruning. Again, this may be appropriate for some varieties, but it does not provide the fruit exposure needed for production of premium wine varieties, especially many vinifera.

Year Four (and Beyond).
Canes or cordons should be fully established and annual growth should fill the available trellis space. Depending on the variety, wine quality may be improved by reducing crop load, usually by removing second and/or third clusters on developing shoots. In regions where winter injury to trunks is anticipated, new trunks can be trained by retaining one or more suckers annually, and used to replace older, winter-injured trunks.

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

Cover crop management is an important consideration in viticulture. Most vineyards are managed with some kind of ground cover in the row middles, while minimizing weed competition near the vines. There are many benefits from growing cover crops in row middles. These include reduced risk of soil erosion and improved soil fertility, as well as health, and structure, and improved footing for operating equipment (especially soon after rainfall). Cover crops are also used to compete with grapevines to reduce excessive vegetative growth, but because both weeds and cover crops compete with grapevines for water and nutrients, an area within the rows is generally kept free of weeds. This is most important in young vineyards when vine roots are becoming established. Once the grapevines have fully developed root systems, weed and cover crop growth can be used to substantially regulate vine growth.

Perennial grasses are commonly used as vineyard cover crops because they are most apt to withstand traffic from vineyard equipment and can tolerate mowing throughout the growing season. Some commonly used species include Kentucky bluegrass, orchardgrass, perennial ryegrass, and various fescues. All of these cover crops can produce dense stands that choke out undesirable weed species, and they usually need to be mowed several times per year. Creeping fescues, as their name implies, have a creeping growth habit that can fill in bare areas, so they may need to be managed with the use of a systemic herbicide such as glyphosate to minimize growth underneath the vines.

There are at least two ways to establish a permanent cover crop in a vineyard. Some growers establish the cover crop first, and then use a systemic herbicide to kill strips in which the vines are then planted. Alternatively, final ground preparation can be made in the spring prior to planting the vines and then seeding the cover crop into the row middles. Seeding is usually most effective in the spring when soil moisture is adequate for seed germination. If a permanent cover crop is not established in the year of vineyard planting, an annual cover crop such as annual ryegrass can be planted in the fall and then killed by cultivation or with herbicide the following spring, at which time a perennial species can be planted.

There are situations in which competition from cover crops in undesirable. The Eastern US ‘Concord’ industry typically uses a single annual application of systemic herbicide in the row middles, applied in late spring prior to grape bloom. Cover crop studies performed by Cornell University (Alan Lakso and Robert Pool) have shown that any actively growing ground cover during the post-bloom period reduces vine size and yield. [1] In another study, cover crops of various widths were established, and vine size and yield was strongly reduced proportional to the amount of competitive sod. [2] In the Eastern U.S. ‘Concord’ industry, vines are typically own-rooted, and vine size strongly affects crop size (big vines make big crops), so increasing vine size by minimizing weed and cover crop competition is desirable.

As opposed to ‘Concord’ production, many wine grape varieties, especially those grown on phylloxera-resistant rootstocks, can produce overly vigorous growth and poor quality fruit. In their treatise on vineyard canopy management, Sunlight into Wine, Richard Smart and Mike Robinson describe the “vicious cycle” of high vigor vineyards where the vegetative growth cycle favors vine growth over fruit production. Excessive shade reduces bud fruitfulness and crop size, further encouraging vine growth and even higher vigor. Smart and Robinson describe two methods to break an excessive grapevine growth cycle – the use of more complex trellis systems to decrease shading, and vine devigoration by root zone management. [3]

For vineyards in arid regions with low summer rainfall, balanced vine growth and improved fruit and wine quality can be achieved using regulated deficit irrigation to devigorate vines by increasing water stress after fruit set. Using careful irrigation management, shoot growth is stopped prior to veraison without excessively stressing the vines, followed by small additional irrigations as needed to maintain leaf function and fruit development during ripening. In addition to direct improvements in fruit quality, other benefits include improved control of diseases and insect pests, which is achieved by facilitating a more open canopy that is less susceptible to pathogens, and by promoting better penetration with chemical sprays. In red varieties, increases in phenolics and tannins can lead to improved flavor and complexity of the wine. [4]

For vineyards in humid regions with higher summer rainfall, induced water stress is more difficult to obtain due to variable patterns of precipitation, but water stress can be obtained through increased root competition. Smart and Robinson describe two methods to accomplish this – increasing vine density (a decision best made prior to planting the vineyard) and between-row cover crops.

Cover crops compete with the vines for water (especially) and nutrients and limit vine root development. Cover crops should be managed as much as possible to devigorate vines to the desired extent without imposing too much drought stress that could reduce fruit ripening or cause premature defoliation (thus making the vines more susceptible to winter injury). In a wet growing season, cover crops can be allowed to infringe on the weed control band under the trellis, and low growing weeds like crabgrass can be allowed to grow to encourage more competition with the vines. In dry seasons, cover crop and weed growth can be controlled using post-emergence herbicides, but in severe drought seasons supplemental irrigation is the best method to ensure that vines do not run out of water completely.

Cover crop management is a necessary component of successful vineyard management. Ground covers are essential to maintaining and improving soil health, thus benefiting the health of the vineyard; cover crop and weed growth can be managed to influence vine growth and canopy characteristics, crop size, and fruit and wine quality in humid growing regions.

[1]  Weed Management, R.M. Pool, et al., 1995.

[2] Substituting water for herbicides: interactions of cover crop extent and irrigation in New York vineyards, Pool, Lakso, and Dunst, 1997.

[3] Sunlight into Wine. Smart and Robinson, 1991. https://doubleavineyards.com/sunlight-into-wine-a-handbook-for-winegrape-canopy-management

[4] Regulated deficit irrigation as a water management strategy in Vitis vinifera production. Wample and Smithyman, 2002.

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

The production of large crops of high quality fruit requires that grapevines be pruned and trained to produce a large area of healthy leaves exposed to sunlight.  Many different training systems have been developed to meet this goal; please see a previous article on the topic, found here: https://doubleavineyards.com/news/grapevine-pruning-with-an-emphasis-on-vineyard-establishment/ .  Depending on the training system employed, additional canopy management measures may need to be used to maximize fruit and wine quality by optimizing fruit ripeness and minimizing the occurrence of fruit bunch rots.  This article will discuss the need for summer canopy management for two popular training systems, Top Wire Cordon (TWC) and Vertical Shoot Positioned (VSP), and canopy management techniques used for VSP.

Commercial vineyard training systems have evolved that maximize the production of high quality fruit with minimum labor input.  For example, in the Eastern United States, ‘Concord’ growers have largely adopted a bi-lateral Top Wire Cordon system referred to locally as “No-Tie” (Top Left).  Two trunks per vine are trained to a top wire, and semi-permanent cordons are established on the wire.  Several one year-old canes, usually 5-8 buds long, are retained in order to reach the desired bud and shoot number.  Once the vines are established and vines are pruned, there is usually no summer canopy management employed (Top Left).

Top Wire Cordon training systems are extremely efficient and should be used where appropriate.  Many native varieties with procumbent, downward growth habits, and even some hybrid varieties with semi-upright growth habits, are well-suited to TWC.  The top right photo shows a ‘Vidal’ vine trained to TWC in a highly productive vineyard in western New York.  ‘Vidal’ has a relatively loose cluster with thick-skinned berries, making it fairly resistant to bunch rots, and cluster exposure to sunlight does not necessarily improve wine quality in this variety.

Unfortunately, top wire cordon systems are not well-suited to grow many varieties, especially vinifera, in the humid and variable climate of the eastern United States.  Vertical Shoot Positioned (VSP) training systems are much better suited for varieties where fruit exposure to sunlight is critical in order to maximize fruit and wine quality and to minimize fruit rots that can have adverse affects on wine quality.  Successful grape production on VSP systems requires the use of several canopy management techniques that are all labor-intensive compared to TWC systems.  These include shoot thinning, shoot positioning, shoot topping (referred to as “summer pruning” or “summer hedging”), and leaf removal in the cluster zone.  Ideally, each operation is timed to be effective and efficient in order to reduce labor inputs.

SHOOT THINNING

Shoot thinning is used in VSP training to regulate shoot density and crop load.  Ideally, 3 to 5 shoots per foot of row are retained at even spacing.  Unproductive shoots should be removed and shoot crowding should be avoided, especially at the “head” area of the vine.  Shoot thinning is best done after the risk of spring frost is over; shoots 4-6” long can easily be removed by hand whereas longer shoots may need to be pruned off with shears, a much more time-consuming task.

SHOOT POSITIONING

VSP training requires the use of two or (preferably) three pairs of catch wires above the fruiting wire, which is usually placed 36” to 42” above ground level so that shoots can be trained in an upright position.  Upright spurs on spur-pruned vines, or upright-growing shoots on cane-pruned vines, facilitate natural growth between the sets of wires, but some hand shoot positioning is also needed.  This can be done most efficiently by making several passes through the vineyard to move the shoots between the sets of wires, starting when the first shoots are long enough to be placed between the first set of catch wires.  Additional passes are made until the majority of shoots have been positioned between the uppermost set of catch wires.

SUMMER PRUNING

Ideally, once the shoots emerge through the top set of catch wires, they will stop growing.  This is not always achievable in our climate, since summer rains can encourage continued shoot growth beyond the desirable length.  If shoots become too long, they will droop over the top set of catch wires and cause undesirable shading of the fruit zone.  This can lead to reduced sunlight exposure in the fruiting zone and cause reduced fruit quality, increase the incidence of disease in the fruit clusters  (especially powdery mildew and botrytis), and reduce bud  fruitfulness in the following year.  In very small vineyards, summer pruning can be done by hand, but usually it is done by hedging the canopy about 6-8” above the top set of catch wires.  Depending on vine growth, summer hedging may need to be done several times per season.

LEAF REMOVAL

In addition to the techniques described above, leaf pulling is often used to maximize wine quality.  Red varieties, especially, can benefit from fruit exposure to sunlight to improve fruit chemistry.  Varieties that are prone to fruit rots (most vinifera varieties fit in this category) benefit from increased air flow around the clusters, which improves drying time after rainfall and also improves fungicide penetration into the canopy and onto the fruit where it is needed.

How much leaf pulling is needed, and when and where, depends on variety and climatic conditions.  Red vinifera growers in hot, sunny climates often pull leaves only on the “shade” side of the canopy (east side of north-south oriented rows, or north side of east-west oriented rows); growers in cooler, cloudier locations may pull leaves on both sides.  Some white varieties can be especially prone to sunburn, so growers often pull leaves only on the “shade” side of the vines, at least initially, but may do some additional leaf removal on the “sun” side later in the season when days are shorter and sunlight intensity is less.  Leaves should only be removed to the extent that their removal aids in fruit exposure, without compromising vine leaf area needed for fruit ripening and bud development for the following year, so should be restricted to the fruiting zone.  Generally speaking, leaf removal should be performed soon after fruit set in order to maximize the benefits of the practice.  The bottom left and right photos show ‘Pinot Gris’ on shoot thinned, shoot positioned VSP, before and after appropriate “shade side” leaf pulling at fruit set, respectively.  All photos in this article were taken on June 21, 2012, about 2 weeks after grape bloom.

For additional reading on this topic, I refer you to Chapter 6 “Grapevine Canopy Management” in the Wine Grape Production Guide for Eastern North America (Andrew Reynolds and Tony Wolf), and Sunlight into Wine:  A Handbook for Winegrape Canopy Management (Richard Smart), two excellent resources for the serious grape grower.

Entire textbooks (or chapters of textbooks, anyway) have been devoted to the topic of pruning, training, and trellising grapevines.  This article will provide a brief overview of the main concepts of pruning grapevines, with emphasis on pruning during vineyard establishment.

Dormant grapevine pruning during vineyard establishment is performed annually with two main goals in mind – training the vine to the desired configuration on the trellis, and building vine reserves to support a grape crop in the future.  Crop control is a third goal of pruning once vines are established, but early vine development should not be sacrificed for small crops in the early life of a vineyard.  Once a vineyard is mature, pruning is used to limit crop size by producing fewer clusters with larger berries and higher quality potential.

Once a vineyard is planted, the single most time consuming vineyard operation is pruning.  Pruning is described as the act of removing parts of a plant, and is performed annually (at least) with the goals of regulating crop size and affecting the location and amount of vegetative growth.  The term “pruning” in this article refers to dormant-season pruning, not summer pruning or hedging that is used to optimize fruit exposure with Vertical Shoot Positioned (VSP) training systems.

Used in conjunction with pruning, training is the act of shaping the vine by arranging it on a trellis.  The choice of training system will have a large effect on the way the vine will be pruned.  The following figure from Cultural Practices for Commercial Vineyards1 describes four training systems, illustrates how a grower should prune vines when using the Umbrella Kniffen training system (a-c), and how the vine should look when mature (g).  Although the position of vegetative growth will change with training system, I chose this illustration to present the concepts of pruning during the establishment of a vineyard and will be referring to it throughout this article.  The entire text of Cultural Practices for Commercial Vineyards can be found at: http://ecommons.cornell.edu/handle/1813/17318

Figure 11 from Cultural Practices for Commercial Vineyards, Jordan, et al., 1981.  (a-c) show a young vine being trained to the Umbrella Kniffen system with double trunk, (d-f) show four different training systems.

Year 1.

Depending on how the vine was treated in the nursery, it will have a few to several buds.  The primary goal in the establishment year is to grow a healthy root system, and the previous illustration indicates one way to accomplish that.  Figure (a) shows the vine after planting and pruned to two shoots or buds.  The idea of restricting growth to only a few buds is to concentrate the energy of the vine into only a few growing points so at least one shoot will develop into a cane that can be selected for growth the following year.  These shoots can originate from the base of the vine and do not need to be tied to a wire, but some method of training is usually desired to keep the vine from sprawling on the ground.  Bamboo stakes can be used to help train the shoots upwards, and plastic grow tubes are often used to protect the young growth from damage caused by animal feeding, chemical herbicides, or mechanical cultivation.  Controlling weed growth to limit weed competition around young vines is especially important in the year of planting, and any clusters that set fruit should be removed in order to direct plant reserves to the root system.

Year 2.

The goals in the year after planting are to begin training growth to the desired training system  and to continue to build vine reserves to support at least a partial crop in Year 3.  This is typically done as shown in Figure (b).  Vines are pruned to a single cane that will produce 6-12 healthy shoots.  If pruning to a high wire training system, the single cane can be tied to the high wire, if possible, and shoots growing on the lower portion of the cane can be removed by hand.  A second trunk can be initiated by retaining a “sucker” shoot near the base of the vine.  Double trunking (maintaining two trunks per vine rather than a single one) is usually preferable in case one of the trunks needs to be replaced due to injury from winter freeze damage or other causes.   If pruning to a low wire training system such as Vertical Shoot Positioned (VSP), then prune to the bud below the fruiting wire and secure to the wire.  Shoot growth in Year 2 should begin to fill the trellis space allotted to the vines.  Any fruit that develops is usually removed by flower or fruit cluster thinning, as leaving more than an occasional cluster for identification purposes is counter-productive because the fruit will compete with vine reserves needed to develop the root system.

Year 3.

The desired shape of the vine should be achieved during the third growing season, and a healthy vine should be able to produce at least a partial crop.  Fruiting canes tied to the trellis become the “semi-permanent” structure of the vines depending on the training system employed.  If not already accomplished, a second trunk should be established.

Training systems for mature vines.

Generally speaking, fourth year and older vines should be capable of producing a full crop.  A training system should be selected appropriate to the variety.  Native American vines (especially) have large leaves and a drooping growth habit, so high wire training systems such as Hudson River umbrella, or other top wire systems, are generally used for them.  On the other hand, vinifera cultivars generally have smaller leaves and upright growth habit, so they are more suited to low wire training systems such as Vertical Shoot Positioned (VSP).  For a schematic depiction of top wire cordon (TWC), umbrella kniffen (UK), vertical shoot positioned (VSP), and Geneva Double Curtain (GDC) training systems, please visit this web site at Ohio State University2:

http://ohioline.osu.edu/b919/pdf/b919_centerfold.pdf

When to Prune? 

Vines are pruned anytime they are dormant.  Cold-tender varieties are usually pruned in the spring so that extra buds can be retained to compensate for buds that did not survive the winter.  Some growers use a “double pruning” system whereby vines are pruned and brush is pulled, but extra buds are left in case there has been winter damage.  In this case final pruning can be done at bud swell; however,  canes removed during pruning are best removed from the trellis when the vines are dormant to minimize shoot breakage while pulling brush.

How many buds do I leave?

Dormant pruning is the primary means of regulating crop size.  Vines pruned too lightly (leaving too many buds) run the risk of producing a high yield of inferior quality fruit that will make inferior quality wine.  Vines pruned to too few buds will reduce crop unnecessarily and vine growth will tend to be overly vegetative and vigorous.  Researchers have developed the method of “balanced pruning” in order to balance vegetative growth with desired yield of mature fruit, and is a system that adjusts the number of buds retained at pruning according to vine size and specific to variety.  Labruscana (native American) varieties tend to have relatively low crop potential per retained bud, so more buds are generally left after pruning (50-60 buds per vine or more might be necessary to produce a moderate yield of 5-6 tons of fruit per acre).  Many hybrid varieties have large clusters and fruitful base shoots, so fewer buds are retained.  In some cases (Vidal and Seyval, for example) fruitfulness is so high that dormant pruning alone does not always limit crop to a desired level, so sometimes clusters are thinned during the growing season.  Many hybrid and vinifera varieties are pruned to 3 to 5 buds per foot of row to produce the desired crop level; for example, vines planted at 6’ intervals between the vines are pruned to 18 to 30 buds per vine.

Suggested pruning formulas for various grape cultivars can be found in the Midwest Grape Production Guide at:  http://ohioline.osu.edu/b919/0008.html

REFERENCES
1. Cultural Practices for Commercial Vineyards, T.D. Jordan, R.M. Pool, T.J. Zabadal, and J.P. Tomkins, Cornell University, 1981.

2. Midwest Grape Production Guide, I. Dami, B. Bordelon, D. Ferree, M. Brown, M. Ellis, R. Williams, and D. Doohan, The Ohio State University, 2005

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

As the 2011 growing season comes to an end, we all know what comes next – winter. In areas where extreme cold temperature or temperature drops occur, winter protection of grapevines may be necessary. By their nature, grafted vines are most susceptible to winter injury, particularly at the graft union. Own-rooted vines are also susceptible to winter injury if temperatures exceed their level of winter hardiness. This article is intended primarily for growers of grafted vines where sub-zero (Fahrenheit) temperatures are likely or possible, but the cane burial techniques discussed can also be used with own-rooted vines grown in extreme climates.

Cold temperatures can kill parts or all of grapevines, depending on the variety and location of the vines. All grape varieties have a level of inherent hardiness; our catalog lists varieties by their level of anticipated hardiness using the “USDA winter hardiness” zones map. Elaborate methods of winter protection are generally not necessary for own-rooted vines grown within their USDA hardiness zone. However, varieties grown where temperatures are colder than their inherent hardiness may need winter protection. Grafted vines are susceptible to winter injury when temperatures fall much below 0°F. They are also susceptible when sudden temperature drops occur, regardless of the cold hardiness level of the scion variety. Areas with continental climates, away from the moderating effects of oceans or other large bodies of water that do not freeze over in the winter, are particularly susceptible to winter injury to grapevines when sudden temperature drops occur.

Winter Injury Avoidance
1. Vineyard site selection. Choose sites with good air drainage so cold air tends to move away from the vineyard. As mentioned, maritime sites are preferred because of the moderating effect of open bodies of water on air temperature.

2. Variety selection. Choose varieties that are hardy at your location. As the saying goes, “It only takes one night” for damage to occur. Absolute cold temperature is the most important factor, but the duration of the temperature extreme also plays a role.

3. Proper vineyard management. Carbohydrate reserves are the vine’s natural antifreeze, and vineyard management should strive to attain maximum levels of carbohydrate reserves at the end of the growing season. This means proper nutrition and pest control, good water relations throughout the season, and avoidance of over-cropping.

4. Winter protection techniques such as covering graft unions and/or fruiting wood on cold-sensitive varieties. Covering (and uncovering) vines on an annual basis is an expensive, labor-intensive method of providing additional winter protection, but may be necessary to ensure live vines and/or fruiting canes for the following season.

Methods of winter protection
1. Insulating with soil. Soil serves as an excellent source of insulation, and winter temperatures just a few inches below the soil surface are rarely more than a few degrees below freezing even with much colder air temperatures. Commercial growers often use a mechanical grape hoe to mound up soil in the fall, and then to remove the mound in the spring. Graft unions on grafted vines should be covered with at least a few inches of soil for the winter months, and the mound should be removed in the spring to prevent scion rooting (roots growing from the scion variety rather than the rootstock variety). If desired, canes can be buried for protection in the winter, and the mound should be removed in the spring so the process can be repeated the following year.

2. Insulating with mulch. Straw, hay, wood chips, and compost can all be used to provide insulation around vines. Several tons of material may be necessary to cover an acre of vines, so the time and expense associated with this practice should be considered. It is certainly a viable practice for growers with small vineyards.

Special considerations when using grafted vines
Grafted vines are often used in grape production as rootstocks can impart desired characteristics to the vines. The introduction of phylloxera to Europe from North America in the 19th century led to the decline and death of European vinifera vineyards. Grafting phylloxera-susceptible cultivars onto phylloxera-resistant rootstocks led to the recovery of the European grape and wine industry. Rootstocks can also provide resistance to nematodes and viruses, and can impart desired growth characteristics to the vines, such as vigor control. However, the graft union is most susceptible to winter injury. In locations where graft unions may be exposed to sub-zero Fahrenheit temperatures, they must be protected over the winter in order to avoid damage. For this reason, it is CRITICAL that graft unions be planted no more than 1-2” above ground level so soil or other insulating materials can be applied to cover the graft unions during the winter months.

The Michigan State University publication Winter Injury to Grapevines and Methods of Protection, written by experts from Michigan, Ohio, New York, and Pennsylvania, is the authoritative publication on this topic.

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

After nearly twelve months of taking care of your vineyards, the last decision you make can be the most agonizing and difficult– when is it time to harvest the fruit?  As grapes mature, they develop aromas and flavors, and the chemical composition of the fruit changes.  Knowing when those factors have reached optimum levels is both an art and a science, and the answer can be different for each variety you grow.

Let’s discuss the science first.  As fruit matures, several indicators of ripeness can be measured.  The most obvious is the sugar content of the fruit, measured as percent sugar or soluble solids and referred to as degrees brix.  A relatively inexpensive refractometer can be used to measure brix in representative fruit samples or in the must.  Juice with 21°-22° brix, if fermented dry, will yield a wine with typical alcohol content of about 12%.  Many American grape varieties  such as Concord, Niagara, and many more, are best harvested long before the fruit achieves anywhere near 22° brix to avoid the development of pronounced “foxy” flavors that most people consider undesirable.  In this case, fruit can be harvested at less than 22° brix and chapitalized by adding sugar to reach the desired alcohol content.  The variety Edelweiss is often harvested at 15°- 16° brix, and Cayuga White at 15° – 18° brix, even though the fruit will continue to gain sugar beyond that point.   On the other hand, many vinifera and hybrid varieties continue to develop better flavors and aromas as they mature, and should be left to hang much longer.  Red varieties will also develop more intense color and softer, more mature tannins.

Titratable acidity and pH are two other common measurements of fruit maturity.  High acid, low pH fruit can make wines that are tart and acidic, while low acid, high pH fruit can make wines that are flat or flabby.  High pH fruit (over pH 3.5 or so) can make wines that are biologically unstable and may be prone to oxidation.  PH and acidity are determined with a pH meter, but obviously every home winemaker will not own one.  If you are working with a winery, the winemaker will likely want to work with you in collecting samples and in determining the pH and acidity of the fruit to assist in determining when the fruit will be harvested.

As opposed to the technical measures of fruit maturity, observations in the vineyard can be just as important in determining optimum quality.  For many varieties, the beginning of berry dehydration can indicate that harvest is near.  Flavor profiles change as the fruit matures.  In some cases, flavors keep developing long into the season, and fruit is left to hang as long as possible until cold weather,  animal damage, brittle cluster stems, or berry splitting dictates the time of harvest.  However, in other cases, flavors “peak” and further maturity is undesirable.  Native American varieties in particular can begin to develop undesirable flavors.  Varieties with muscat parentage tend to reach a peak of desirable flavors which then decrease with further maturity.  Frequent sampling and tasting in the vineyard (and experience) can help you recognize the best time to harvest each of the varieties you grow in order to achieve optimum wine quality.

For a more complete discussion of this topic, and additional references,  consult  “Wine Grape Quality: When is it Time to Pick” by W. Gill Giese in Wine Grape Production Guide for Eastern North America, edited by Tony Wolf, a must-read book for anyone serious about growing grapes and making fine wine.