Rick Dunst, Viticulturist, Double A Vineyards, Inc.

Over the years (25 and counting!), Double A Vineyards has built a large clientele with varied interests that range from commercial vineyard and winery owners to the backyard hobbyist. This article is aimed at the latter, especially our customers who decide they want to grow grapes or grapevines in their backyard, but who may or may not know what to expect. We hear almost daily from new growers: “I didn’t know what I was getting myself into.” Rest assured, even those of us who have chosen grape growing, winemaking, and perhaps even the grapevine nursery business, ask ourselves some variation of this question on a regular basis.

WHY DO YOU WANT TO GROW GRAPES?

There are a lot of answers to this question. The most common are “home winemaking,” “growing grapes to eat,” “shade from an arbor,” and my favorite, “I thought it would be cool.” These are all legitimate reasons to grow grapes, and they all require a basic understanding of what it takes to grow a grapevine to fruition (pun definitely intended).

WHAT DO GRAPEVINES NEED?

Everyone knows that plants need sun, water, and nutrients to grow, and this is true of grapevines. But grapevines also need good air movement and soil drainage to be grown successfully. Why is this? Although grapevines vary widely in their susceptibility to disease, every variety of grape is susceptible to one or (typically) more diseases or insects that can attack the leaves, fruit, and (sometimes) roots. While some intervention, typically in the form of pesticide application, is necessary to grow healthy leaves and fruit, grapevine access to sun, water, nutrients, good air movement, and soil drainage should be primary considerations when deciding where you should locate your vineyard.

SELECTING A LOCATION TO GROW GRAPES

This section could easily be titled, “Where should I plant my vines?” Or even better, “Where SHOULDN’T I plant my vines?” You should plant your vines in an open location that receives as much direct sunlight as possible, with good airflow, and which rarely (if ever) has standing water. Planting along a chain-link or similar type of fence on the perimeter of your property is OK as long as it is not shaded by trees. Planting along a solid wood fence is less desirable since air flow will be impeded and the vines will be in the shade for at least part of the day. Planting next to the house is usually a mistake since the vines will be growing in at least partial shade. Additionally, airflow will be impeded and soil may be saturated for several days, especially if located near gutter downspouts.

Grape varieties differ substantially in their susceptibility to diseases and insects, and grape growers differ in their willingness to apply measures (especially pesticides) to control them. Backyard growers should select varieties that are winter hardy at their location and are less susceptible to diseases such as black rot, powdery mildew, downy mildew, and botrytis. These diseases are endemic to humid regions across the United States. This information can be found in our Grapevine Variety Characteristic Chart. Growers need to understand that low susceptibility to disease does not mean the vines are immune to disease. During periods of extended rainfall, disease can become established on cultivars even with low disease susceptibility, and once they become established, disease inoculum will be present that can further spread the disease later in the growing season, as well as into the next season.

Regardless of what variety is selected and grown, some pesticide applications will likely be needed to grow healthy vines with disease-free fruit. Information about pesticides available to the homeowner can be found in a recent article on our website entitled “Grape Pest Management for the Homeowner.” Generally speaking, native and hybrid varieties are less susceptible to diseases than are vinifera. Vinifera varieties are especially problematic for the small grape grower as they are very susceptible to most or all of the major diseases and need to be sprayed more often than native and hybrid cultivars. Varieties that are susceptible to Botrytis and other fruit rots (including some hybrid cultivars) are especially problematic as there are no pesticide products available in homeowner-sized packages to control these diseases.

GRAPEVINE ARBORS

Grapevine arbors deserve some special consideration. Typically, the homeowner is looking for a shaded entry to the house, or perhaps a shaded backyard area during the summer. The photo that accompanies this article shows an attractive grapevine arbor at the Double A residence planted to 3309 Couderc (commonly referred to as 3309 or 3309C), a grapevine variety typically used as rootstock. Why 3309? It is winter hardy, disease resistant, and produces no fruit (it is a male-sterile variety). Winter hardiness means that you don’t have to worry about re-training from ground level following a harsh winter. Disease resistance means you never have to spray it (although, in a wet season, you may get some downy mildew established on the shaded parts of the canopy). No fruit means not dealing with birds that are attracted to ripening fruit and the associated bird droppings, nor over-ripe fruit falling to the sidewalk underneath the arbor. It may be possible to grow fruiting varieties on an arbor, but do you really want to walk, eat, or entertain guests in an area that requires pesticide applications and may have fallen fruit or bird droppings beneath the arbor, and may be attractive to bees if ripe or overripe fruit is present?

GRAPEVINE TRELLIS

As mentioned, with the exception of growing grapevines on an open (chain-link) fence, training vines along a solid fence or next to the house is undesirable due to shade and lack of air movement. These unfavorable conditions impede drying of leaves and fruit, and lead to an increase in disease pressure.

Trellis construction is an art in itself, the goal is to install a trellis that requires little maintenance. Wood posts are usually preferred, especially if vines are trained to a high wire training system. Metal posts with notches for catch wires are more appropriate if a vertical shoot positioned system is used. Newly-planted grapevines can be trained on a bamboo stake during the first growing season. Depending on how much the vines grow the first year, a low wire may be necessary for vine training during the year of planting; in any case, trellis construction needs to be completed prior to the initiation of vine growth in the second year so that the vine can be attached to the trellis and trained to the desired system. Several links with references pertaining to training systems and trellis design and construction can be found at the end of this article.

WEED CONTROL

One of the most common problems we see with grapevine establishment is lack of weed control. This is the time of year that we receive daily emails from new growers wondering why their vines are not thriving in the middle of a manicured lawn, or worse, in an unmowed field with weeds or sod towering over the newly-planted vines. Established grasses have extensive root systems that quickly overtake bare areas, such as the small weed-free patch you may have established around young vines. For further discussion about weed management in vineyards, view last month’s article.

GRAPEVINE SPACING

Spacing of grapevines is determined by many factors, including inherent vigor of the variety and of the soil. Our Grapevine Characteristic Chart lists spacing most commonly used by commercial growers to produce these varieties, which is based on the optimum spacing to produce healthy vines with high quality fruit. Planting vines too close together can result in vine shading that results in poor fruit quality and an increase in disease and the need to spray fungicides. Planting vines too far apart results in less fruit production than is possible, which is an especially important consideration when space is limited. If there is sufficient space to produce the desired quantity of fruit, consider using wider spacing between vines to increase grapevine canopy exposure to sunlight and air movement around the vines.

ORGANIC GRAPE PRODUCTION

We often get inquiries from our customers who find they have disease issues in their grapevines but who want to grow their fruit “organically.” Organic farming emphasizes cultural practices aimed at reducing chemical inputs (such as soil cultivation instead of herbicide use), and plant sanitation practices such as removing disease inoculum from the vineyard. However, the term “organic” is often confused with “grown without the use of pesticides,” and this notion is rarely true. Organic farmers typically follow guidelines established by state and federal agencies that prohibit the use of synthetic pesticides but allow the use of naturally-occurring substances with pest control activity.

Double A Vineyards offers several pesticides for the homeowner, some certified as organic, and some not. Organic pesticides include the following:

Elemental sulfur controls powdery mildew only. Unfortunately, many of the native and hybrid varieties that are less susceptible to certain diseases are sulfur-sensitive, meaning they are injured from sulfur application. Even varieties that are considered “sulfur tolerant” can be injured if applications are made when temperatures are above 85˚F.

Horticultural spray oil, a petroleum product, controls young powdery mildew infections and some insects by smothering them. Repeated use of oils can reduce grapevine photosynthesis and result in a decrease in fruit sugar content at harvest.

Copper fungicides provide good control of downy mildew, some control of powdery mildew, and only moderate control of black rot. Black rot is often referred to as the “Achilles Heel” of organic grape production in the Eastern US as there are no organically certified fungicides that provide the level of black rot control that can be obtained using certain synthetic fungicides. Repeated applications of copper often lead to injury to grapevine foliage and can be associated with reduced photosynthesis and sugar accumulation in fruit.

There are many reasons for wanting to become a grape grower. Being realistic about what you can grow at your location, where your vineyard should be located, and what inputs are needed will increase your likelihood of success.

References:

Training Systems:

https://www.doubleavineyards.com/Images/TopWireCordon.pdf

https://www.doubleavineyards.com/Images/VSP.pdf

https://www.doubleavineyards.com/Images/MidWireCordon.pdf

Trellis design and construction:

https://hortnews.extension.iastate.edu/2007/6-20/grapetrellis.html

https://hortnews.extension.iastate.edu/1995/5-5-1995/trell.html

https://www.doubleavineyards.com/p-872-vineyard-establishment

https://www.canr.msu.edu/resources/vineyard_establishment_1_pre_plant_decisions_e2644

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

Chemical pest management options for growers with only a few vines are limited. While non-restricted use pesticides can be purchased and used by anyone (meaning, anyone who reads and understands the pesticide label prior to application and applies it legally), they usually come in package sizes intended for commercial growers with at least several acres of vineyard. This article is intended for the small/homeowner/backyard/hobbyist grower producing a small amount of grapes for their personal use (or to share with friends).

While chemical control options are usually necessary in humid regions, they should not be considered the first line of offense. Grapevine varieties differ substantially in their relative resistance to disease (Grapevine Characteristics Chart), so consideration should be given to planting the least disease-susceptible cultivar that has sufficient winter hardiness to thrive at your location. Typically, vinifera cultivars are much more susceptible to grape diseases such as powdery and downy mildew, black rot, phomopsis, and in some cases, botrytis and other fruit rots, than many American and hybrid varieties. Where possible, grapevines should be planted in areas with good air movement and full-day sun to aid in drying, which will reduce the chance of disease development. We often see crop failures in wet, fenced-in backyards surrounded by trees and buildings. Finally, inoculum for some diseases can be reduced by removing infected material, such as black rot mummies or anthracnose cane lesions, from the vineyard.

There are several grapevine diseases of concern to grape growers in humid climates with spring and summer rainfall, including black rot, powdery mildew, downy mildew, phomopsis, and anthracnose. If you need assistance in determining which disease(s) are an issue in your vineyard, refer to these University fact sheets:

Fact sheet on black rot

Fact sheet on powdery mildew

Fact sheet on downy mildew

Fact sheet on phomopsis

Fact sheet on anthracnose

It is important for the grower to understand that chemical controls for grapevine diseases are usually made on a preventative basis, meaning that control measures should be taken before infection has taken place. Once you see disease infection in the vineyard, sprays can be applied to prevent or minimize future infections, but existing infections will not be eradicated, and in most cases they provide inoculum to further spread the disease during the current growing season.

Double A Vineyards offers several homeowner chemical fungicides on our website that, if used on a preventative basis at timely intervals, provide control of all five listed grapevine diseases. These products include Spectracide Immumox and several Bonide products including Captan-50% WP, Fruit Tree Spray Concentrate (a pre-mix of Captan plus insecticide), Sulfur Plant Fungicide, All Seasons Spray Oil, and Copper Fungicide. While the following information is based on information provided on product labels and on many years of experience, Double A Vineyards will not be held liable for any reason should our customers decide to use these products. It is the responsibility of the applicator to read and understand the pesticide label prior to application, and apply it in legal fashion according to local, state, and federal regulations.

Application rates for all the products listed in this article are based on an amount of product per gallon of spray mix. Sprays should be applied just prior to the point of runoff on leaves and clusters.

Spectracide Immunox (1.25 fl. oz. per gallon) + Bonide Captan-50% WP(1.5 Tbsp. per gallon) is a basic homeowner spray mix that controls anthracnose, black rot, powdery mildew, downy mildew, and phomopsis. Spectracide Immunox contains the same active ingredient, myclobutanil, as the commercial product Rally. Unlike any of the other homeowner products, it is labeled for control of anthracnose and black rot, and it also controls powdery mildew. Spectracide Immunox should be applied starting at 1-3” shoot growth and can be reapplied every 14 days up to a maximum of 5 applications per season. Sprayed at 1.25 fl. oz. per gallon, one pint container of Spectracide Immunox makes 12.8 gallons of spray mix. Captan should be added for control of downy mildew and phomopsis. Captan provides some suppression of black rot, but should not be depended upon to control the disease under high pressure. Captan can be applied at 10-14 day intervals up to the day of harvest. Do not mix Captan with or closely follow an oil spray, and do not mix Captan with highly alkaline materials such as hydrated lime. Sprayed at 1.5 Tbsp. per gallon, one 8 oz. container of Bonide Captan makes approximately 18 gallons of spray mix.

For control of insects such as flea beetle, Japanese beetle, rose chafer, grape berry moth, leafhoppers, and mealybugs, substitute Bonide Fruit Tree Spray Concentrate (1.5-2.5 Tbsp. or 0.75-1.25 fl. oz. per gallon) for Captan in the above mix, or apply as a separate spray when insects are present. Fruit Tree Spray Concentrate is a combination of Captan and two insecticides, Malathion and Carbaryl. Two applications per year are permitted with a minimum re-treatment interval of 14 days. Do not spray Fruit Tree Spray Concentrate when temperature is above 85°F nor within 7 days of harvest. Sprayed at 0.75 – 1.25 fl. oz. per gallon, one pint container makes 12.8 to 21.3 gallons of spray mix.

For increased control of powdery mildew, Bonide Sulfur Plant Fungicide (1-3 Tbsp. per gal.) can be added to any spray on sulfur-tolerant varieties in a tank mix or can be alternated with Spectracide Immunox. This is a useful spray on varieties very susceptible to powdery mildew and tolerant of sulfur applications. Sulfur can be substituted for Spectracide Immunox for control of powdery mildew, but sulfur does not control black rot. CAUSES INJURY ON SULFUR-SENSITIVE VARIETIES – consult Double A Vineyards’ Grapevine Characteristics Chart for varietal sulfur sensitivity. Applied at 1-3 Tbsp. per gallon, one 4 lb. package of Bonide Sulfur will make at least 50 gallons of spray mix.

Bonide All Seasons Spray Oil (2.5-7.5 Tbsp. or 1.25-3.75 fl. oz. per gallon) controls certain insect pests and young powdery mildew infections by smothering them. For powdery mildew control, sprays can begin before bloom and repeat every 10 days (or up to 3 weeks). Good coverage is essential for control. Under high disease conditions, such as when the disease has already begun to establish and powdery mildew colonies are visible, the label recommends use of 7.5 Tbsp. per gallon and/or shorter spray intervals. Insects including mealybug, mites, and leafhoppers can be controlled by smothering them with oil. Do not mix All Season Spray Oil with Captan and do not apply within 14 days of a Captan application. Do not mix All Season Spray Oil with sulfur nor apply when sulfur is on the foliage. Do not mix All Season Spray Oil with copper more than once per season nor when fruit is present. Do not apply All Season Spray Oil if temperature is >90°F or less than 40°F. Table grapes cannot be sprayed with All Season Spray Oil within 60 days of harvest. Oil application will remove the bloom on grape skin. Sprayed at 1.25-3.75 fl. oz. per gallon, a one-quart container of Bonide All Season Spray Oil makes 8.5 to 25.6 gallons of spray mix. Commercial growers typically spray oil in a 1.5-2% solution, or 2-2.5 fl. oz. per gallon, so a one-quart container would typically make 12.8 to 16 gallons of spray mix.

Bonide Copper Fungicide (2-26 oz. per gallon) provides control of downy mildew and suppression of black rot, powdery mildew, and phomopsis. Applications can be made throughout the season. Copper can be used as a substitute for Captan in any mix, or as a late-season spray, but copper can cause injury on many grape varieties, especially after repeated applications or under slow drying conditions. Do not mix copper with oil. Copper controls downy mildew but provides only suppression of phomopsis, black rot, and powdery mildew, so it should not be depended upon for control of these diseases under high disease pressure. CAUSES INJURY ON COPPER-SENSITIVE VARIETIES. Sprayed at 2-26 oz. per gallon, one 16 oz. container of Bonide Copper makes 0.6 to 8 gallons of spray mix.

Customers often ask how many vines can be sprayed using one or more containers of a particular product. The answer is: it depends. All of the homeowner pesticides discussed in this article are applied by mixing a rate of product per gallon of water, and application should obtain thorough coverage of leaves and clusters. The number of vines you can spray with a gallon of spray mix will depend on the time of the season and the amount of growth on the vines. Commercial growers often spray at 50 GPA (gallons per acre) for pre-bloom sprays when the canopy is not yet completely filled, while later-season sprays might require 100-200 GPA to obtain good coverage.

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

Small vineyard owners often find that they need to spray chemicals for control of weeds, insects, and disease, but can’t justify the expense of a tractor-operated sprayer (not to mention the tractor). The need for chemical applications to control grapevine diseases can be minimized by selecting cultivars that are relatively disease-resistant, and by planting the vineyard in a location with full sunlight and good air movement. However, in humid climates, some fungicide applications are almost always needed to maintain a healthy canopy of leaves and/or disease-free fruit. Most fungicides are applied to prevent the development of diseases, while insecticides are usually applied when insects are present and have met or exceeded established thresholds. In very small vineyards weeds can be controlled by hand-pulling or hoeing, or by applying organic or synthetic mulches, but larger vineyards often require the application of chemical herbicides. Finally, wildlife predation by deer, rabbits, and birds is sometimes accomplished with the use of exclusion devices such as fences and netting, but repellant sprays are sometimes needed to minimize predatory damage to young vines or to fruit.

There are many brands of backpack sprayers on the market that are completely hand- (and foot-) powered. Double A Vineyards sells a “Deluxe” Solo brand sprayer that holds 4 gallons of water or spray mix and has a pressure gauge to ensure an even application rate. The sprayer is pressurized with a hand lever pump. While spraying, keep pressure constant by pumping down on the lever and maintaining a steady reading on the pressure gauge. The Solo Deluxe sprayer includes several nozzle types. Many standard agricultural spray tips can also be used – use whatever nozzle gives you the spray coverage you are looking for.

When making foliar applications of fungicides or insecticides to the canopy, thorough coverage of the target (leaves and/or fruit, depending on the pest to be controlled) is necessary. Canopies need to be sprayed from both sides of the row. Application instructions found on the label of the product you are using can be based on an amount of pesticide per volume of spray mix or as an amount of product to use per acre of vineyard. Examples include the following:

Some pesticides packaged for the homeowner provide instructions based on an amount of pesticide per gallon of spray mix. For example, label instructions for Bonide Captan 50WP state, “Use 1 to 1 ½ Tbs. per gal. of water. Apply sufficient spray volume to provide thorough, even coverage…. Use the lower rate when spraying less susceptible grape varieties or when conditions are less favorable for disease development. Use the higher rate on susceptible grape varieties and during periods of weather highly favorable for disease development.” In other words, mix the desired amount of product per volume of water, and apply so that all target fruit and foliage is covered, but not so much that the spray is dripping from the canopy. Another example of a pesticide that is applied as a percent solution is JMS Stylet Oil, often applied to control powdery mildew. The stylet oil label instructs, “Apply at 1-2 gal per 100 gal. water (a 1-2% solution). Spray for optimum coverage of leaf surfaces. For powdery mildew control, use the higher rate … when disease conditions are severe.” In order to achieve optimum coverage, sprays should be applied to, but not beyond, the point of runoff.

As opposed to application rates based on an amount of product per volume of water, most commercial pesticide products are labeled for application at an amount of product per acre of vineyard. This type of application will require careful sprayer calibration. Let’s use the example of Microthiol Sulfur, which is labeled at application rates ranging from 3-10 lb. per acre per application for control of powdery mildew, and you want to apply this product at a typical application rate of 5 lbs. per acre. In order to make this application correctly (and legally), you need to know how many vines there are in an acre of your vineyard, and how many vines you can spray with a given volume of spray solution. Sprayer calibration should be performed using a known volume of clean water in the sprayer. For example: your vineyard is planted at 8’ x 6’ spacing, with 908 vines per acre (determined from the table in our catalog, or by using this formula: Vines per Acre = 43,560/ (feet between rows x feet between vines. 43,560 is the number of square feet in an acre). Fill the sprayer with a known quantity of water, and spray the vines to obtain the desired coverage from both sides of the vines until the sprayer is empty to determine how many vines are sprayed (alternatively, spray the vines from one side of the row and divide the number of vines sprayed by 2). For this example, let’s assume you spray 10 vines from both sides with 1 gallons of water. Divide the number of vines per acre by the number of vines sprayed with one gallon of water to determine how many gallons of water are necessary to spray one acre of vines. In this example, 908 vines per acre / 10 vines sprayed with one gallon = 90.8 gal./acre. It will take 90.8 gallons of water to spray one acre of grapes. Since you want to spray 5 lb. sulfur per acre, mix 5 lb. (80 ounces) sulfur per 90.8 gallons, or 0.88 oz. sulfur/gal. Use a postal scale or other accurate scale to weigh the sulfur. Dilute spray volumes are usually in the range of 50 to 100 gal. per acre.

Herbicide calibration can also be based on an amount of product to be used per gallon of water or on a per acre basis (but please read the next paragraph for one important difference). Glyphosate herbicide (original trade name: Roundup) can be applied according to label instructions using an amount of product per gallon of water, with the product rate varying depending on the weed species to be controlled. Glyphosate is a systemic herbicide (meaning it is taken up by mature leaves on actively growing plants and translocated throughout the plant). Glyphosate is more effective at higher concentration, so spraying to runoff is not necessary.

Pre-emergence herbicides are applied on a per-acre basis, but an important distinction needs to be made – herbicide rates are determined on the basis of a rate PER ACRE OF LAND SPRAYED, not per acre of vineyard. To determine how many acres of land are sprayed per acre of vineyard, divide the row width by the herbicide band width. For example, if you are spraying a 32” herbicide strip in a vineyard with 8’ rows, you would spray the desired amount of herbicide on 3 acres of vineyard (96” row width / 32” band width = 3 acres of land sprayed per acre of vineyard). Using the same example vineyard used for foliar spraying (8’ x 6’ spacing)), there are 908 vines per acre. Assume you are spraying a 32” herbicide band, so you will spray 1 acre of land in 3 acres of vineyard, or 2,724 vines. For this example, let’s assume 1 gallon of water sprays 100 vines from both sides (or 200 vines from one side). 2,724 vines per acre sprayed / 100 vines sprayed with one gallon of water = 27.24 gallons per acre sprayed. Mix the amount of herbicide desired (i.e. 4 lbs. per acre in 27.24 gal/acre = 0.15 lb. or 2.35 oz./gal.). Herbicides are usually applied at 25 to 40 gal. per acre sprayed.

When applying herbicides with a backpack sprayer, I typically use a Tee-Jet 8004 flat fan nozzle. The “80” in the nozzle designation indicates the angle of spray delivered – use of a higher degree tip would require holding the nozzle closer to the ground for making a band application of herbicide, and would make applications of post-emergence herbicides such as glyphosate (Roundup) more difficult when herbicide contact with grapevine foliage needs to be avoided. The “04” indicates the volume of spray that will be delivered – a lower numbered nozzle delivers less spray volume at the same operating pressure, and a higher numbered nozzle more. In my experience using the Tee-Jet 8004 nozzle spraying herbicide in a 16” band on each side of the row, at a comfortable walking pace and 35 psi, covers 1 acre of land sprayed with 40 gallons of mix. Each operator should calibrate their sprayer at their own pace, using the selected nozzle type, size, and operating pressure.

Winter injury caused by low winter temperatures is an important limiting factor to grape production in many regions the United States. Our Grapevine Characteristics Chart lists grape varieties by their winter hardiness according to USDA hardiness zone. Hardiness is determined by using a number of sources, including university publications, variety release bulletins, and our own and other grower’s experiences.

A hardiness zone is a geographically-defined area in which a specific plant species (in this case, a grape cultivar) is capable of growing. The hardiness zone is defined by the average minimum temperatures of the zone (see chart on the accompanying map). Vines that are described as “hardy to Zone 7” means the vine can withstand a minimum temperature of 0°F. A more winter-hardy vine that is “hardy to Zone 6” can tolerate a minimum temperature of minus 10°F, and a vine “hardy to Zone 5” can withstand temperatures down to minus 20°F.

Most Vitis vinifera cultivars are hardy in Zones 6 or 7, meaning healthy vines can survive temperatures from zero to minus 10°F. Most American (Vitis labruscana) and hybrid varieties, including recent releases from the Cornell grape breeding program, are hardy to Zone 5 (hardy to -10°F to -20°F), and some of the newer “super hardy” cultivars developed in the Upper Midwest are hardy in Zones 3 or 4 (the hardiest of these varieties are hardy to about -40°F).

The U.S. Department of Agriculture maintains several websites related to the 2012 USDA Plant Hardiness Zone Map, which is based on average annual extreme winter temperatures from 1976 to 2005.http://planthardiness.ars.usda.gov/PHZMWeb/ allows you to locate your hardiness zone by entering your zip code.http://planthardiness.ars.usda.gov/PHZMWeb/InteractiveMap.aspx gives you access to an interactive map that shows the zones at higher resolution.

Since 1960, the USDA has released several versions of hardiness zone maps for the United States. These maps categorize locations suitable for winter survival of a rated plant in an average winter. Plant Maps maintains a website with the 1990 USDA Hardiness Zone Map that was based on data from 1974 to 1986. Interestingly, the 1990 map identified many areas as colder than did the original map issued in 1960, due to several severely cold winters in the eastern and central US during the data gathering period.

One of the drawbacks of using the USDA information is that the hardiness zones are based on average conditions, not extreme ones. Winter minimum temperatures can easily be 10°F colder in a severe winter than in an average one. For example, the 2012 USDA information considers Fredonia, NY, to be in hardiness zone 6b, meaning that the average winter minimum temperature from 1976 to 2005 was zero to -5°F. However, extreme winter minimum temperatures in Fredonia reach -15°F about once per decade. A relatively hardy vinifera cultivar such as Riesling (hardy to about -10°F) has the potential to produce a full crop of fruit in Fredonia most years, but substantial damage can occur in colder than normal winters, resulting in significant bud mortality (which will result in less than a full crop the following season) and trunk damage (which will result in the need to retrain the vines). In severely cold winters such as 1994, when temperatures dropped to -16°F with little snow cover and unprotected graft unions, Riesling vines did not survive in some plantings, and replanting of entire vineyards was necessary. Since the USDA maps refer to average conditions, and since the 1990 map is more conservative, I prefer using the 1990 information when making varietal recommendations to growers.

The USDA maps have additional limitations. Temperature variations from the average are more extreme in continental climates than in maritime regions (the extremes are more extreme). The maps do not take snow cover into consideration; snow is an excellent insulator that can protect the base of vines and roots from freeze damage. The maps also don’t take into consideration effects such as elevation. The microclimate at the bottom of a slope with little air drainage will likely be much colder on a still winter night than a site at mid-slope. Finally, the maps become less reliable west of the 100th meridian (central North and South Dakota through central Texas), since areas with low humidity have even more potential for temperature variations than those to the east.

There are many factors that influence whether or not a specific grape selection will survive and be capable of producing high quality fruit at a certain location, including winter hardiness, seasonal Growing Degree Day accumulation, length of growing season, and risk of spring frost. The USDA hardiness zone maps can be used to help determine an appropriate variety to plant in a given location keeping in mind the limitations discussed in this article.

Rick Dunst, Viticulturist, Double A Vineyards, Inc. 

Now that harvest is over and winter is approaching, the staff at Double A Vineyards is starting to get a lot of phone calls and e-mails from our customers asking for assistance in selecting appropriate varieties to grow on their sites.  While many of our customers know exactly what they want, others are just getting started at growing grapes and may not know which varieties are best suited for their vineyard location.  Grape varieties differ in their tolerance to winter low temperatures; they bud out in the spring at different times, making them more or less susceptible to spring frost; and, they require a certain amount of heat units and length of growing season to fully ripen at a given location.  Knowing the limitations of your site is largely a matter of personal experience (and that of your neighbors), and our catalog and website contain a wealth of information that can help you decide on a grapevine variety suited to your site.  This article will focus on the limitations of both site and variety, and where to collect information that will help you determine the suitability of your vineyard site to produce ripe fruit from a specific grape variety.

Winter Hardiness

A variety’s lack of tolerance to low winter minimum temperatures is an obvious limiting factor to grape production in many parts of the United States.  Our catalog lists grape varieties by their winter hardiness according to USDA hardiness zone.  Most vinifera varieties are hardy in Zones 6 or 7, meaning that these varieties should be hardy to about 0° to -10°F, if they are managed well.  Native American and hybrid varieties have a much broader range of winter hardiness, with some of the newer varieties from breeding programs in Minnesota and South Dakota being hardy to an anticipated -30° to -40°F!  This hardiness information can be used along with the information provided on the USDA hardiness zone map to determine whether or not a variety may be suited to your region (more on the choice of that wording in a minute).

Our website has a link to Plant Map’s site that can determine a location’s USDA hardiness zone by postal zip code: http://www.plantmaps.com/.  While the information derived from the USDA map is useful, it has limitations.  USDA hardiness zones describe the “macroclimate”, the generally prevailing climate of a large geographic region.  However, the “microclimate” of a specific vineyard site is just as important.  For instance, the microclimate at the bottom of a slope with little air drainage will likely be much colder on a still winter night than a site at mid-slope.  When you are attempting to assign a hardiness zone to your site, make sure you have considered the microclimate at your specific location.

Spring Frost Tolerance

The likelihood of a freeze event in the spring is another consideration.  Maritime climates are influenced by large bodies of water that cool nearby land masses, thus delaying bud development in the spring.  In comparison, continental climates are subject to wider temperature fluctuations so that days are warmer and nights are colder, leading to earlier bud development and the increased likelihood of spring frost or freeze damage to the emerging buds.  There are two major factors that can influence the likelihood that a grape variety can withstand a spring cold event to produce a crop.  The most important is the time of bud development in the spring.  Some varieties inherently “break bud” later in the spring than others, thus making them less susceptible to a spring cold event.  Our Grapevine Characteristics Chart lists relative bud break information for many of our varieties (this is a work in progress and will be updated as we collect data in future growing seasons).  Varieties with differences in bud break of a few or several days can mean the difference between a crop largely lost to spring frost and a full crop of a later budding variety.

The second factor influencing successful grape production where spring frosts are likely is the ability of a variety to produce a crop, or at least part of a crop, from secondary buds that force after the primary buds have frozen.  In our experience, hybrid varieties are more likely to be capable of producing moderate crops from secondary buds than are native or vinifera varieties.

Length of the Growing Season and Growing Degree Days

In addition to knowing the likelihood that a given variety will survive winter and spring cold events, you should also make sure the variety is likely to fully ripen at your location.  Some short-season grape varieties may be able to ripen in a season as short as about 150 days (i.e., last anticipated spring frost date about May 1, and first anticipated fall frost date about September 30), while others require 180 days or more to ripen.  There are many sources of growing season information, including this NOAA site with a national map:
www.ncdc.noaa.gov/oa/climate/freezefrost/frostfreemaps.html

You can also find this information at the state and (sometimes) county level; the more detailed the information you can find for your specific locale, the more useful the information will be.

Growing Degree Days

The fourth factor in determining whether or not your climate is suitable for a specific variety is knowing the amount of heat units, or Growing Degree Days (GDD), your location receives.  The Weather Channel is an excellent source for this information:http://adstest.climate.weather.com/outlook/agriculture/growing-degree-days. GDD information is provided for a specific growing season, as well as long-term averages.

Our catalog lists each variety by time of harvest season: early, mid, or late.  Growers with shorter, cooler growing seasons will want to concentrate on early harvest season varieties, while those with warmer, longer growing seasons should focus on later harvest season varieties.  If you have questions about the suitability of a specific variety for your location, we suggest you make use of these resources, and as always, feel free to contact me at rick.dunst@doubleavineyards.com if you need further information.

A Quick Comparison of Potential Vineyard Locations

Using the information provided in this article, I determined the general characteristics of two locations where grapes are grown commercially – Hermann, Missouri, in the heart of Missouri grape country, and Fredonia, New York, in the heart of the Lake Erie Concord Grape Belt and home of Double A Vineyards, Inc.  Both locations are in Zone 5, so winter minimum temperatures may go as low as about -15°F, and the length of the growing season at each location is about 180 days.  The major difference in the two locations is that Herman, Missouri, receives an average of about 3250 GDDs per season, while Fredonia receives an average of about 2650 GDDs.  Norton (Cynthiana), Chambourcin, and Chardonel are all varieties that are hardy to at least Zone  5, and have relatively late bud break in the spring, so would be expected to thrive in both climates.  The difference is that Hermann has more than sufficient heat units to ripen these cultivars in a typical season, while the Fredonia location typically has marginal heat units to ripen Chambourcin and Chardonnel, and inadequate heat units to ripen Norton/Cythiana.  The Missouri wine industry produces some marvelous examples of Cynthiana, Chambourcin, and Chardonel wines, while growers in the Fredonia area produce many native, hybrid (and a few vinifera) varieties that are suited to the climate, but that require far fewer GDDs than are needed to fully ripen a cultivar such as Cynthiana/Norton.  Consider all the climatic characteristics of your unique location when selecting an appropriate grape variety to grow.