Photo: Somewhere mysteriously in California
Grapes are an economically important commodity, supplying fresh, dried, and processed markets worldwide. Although grapes are not a crop you immediately consider a beneficiary of CEA technology, it may be possible to adapt field agriculture, putting in measures to circumvent climate change and disease.
The last few years I’ve been attempting to grow my own grapevine indoors, so when Chris Higgins shared the main photo I felt excited to learn how they were using LED lights to help fruit mature on vines in California.
Could CEA also work for my grapevines?
Scotland is not known for wine but with changing climates and carefully chosen hardy varieties it could provide some competition for our national drink. Success at home is just around the corner as I begin season three with my black Hamburg grape (Schiava Grossa) grafted on S04 rootstock. It’s hopeful too, as earlier than expected it is producing trusses. The learning curve is not as steep as you may think and the trick is to not give up with a fruitless vine.
We will take a look at the growing environment, the diseases that can be encountered and the pests that need to be eliminated by controlling some of the processes. Then we will examine some real Californian vineyards and how they are adapting and integrating CEA technology to increase efficiency and yield, battling against ever changing climates and earlier than predicted seasonal frosts.
Year 3 indoors black Hamburg (dessert grape) in central Scotland
Wine has an important role in world trade
Grapes were one of the earliest fruits cultivated for use as a beverage, and statues in ancient Roman culture were often adorned with grapes and wine decanters. In fact, many of the production principles first developed in ancient Rome can be found in winemaking today. Wine is classed as a cultured beverage and body, flavor, aroma, keynotes and vintage all play a part in how we decide to consume it. Aside from commercial vineyards, many vines can be cultivated under glass. This can be a lean-to, a conservatory, a polytunnel or a glasshouse, it doesn’t really matter. Mine are grown in a conservatory with great levels of natural light and temperatures rising to 105°F which helps ripen the fruit.
The global wine market was valued at USD 417.85 billion in 2020 and growth is expected to expand to 6.4% CAGR by 2028. According to a recent report Italy, France, and Spain were the top three producers of wine worldwide as of 2022. In the Americas, Chile has the leading share of exports, almost three times more than the USA and Canada. Changing consumer preferences are evident with demand for fresh fruit, looking for year-round availability and consumers more willing to pay more for imported out-of-season fresh grapes.
Growing and Grafting Vines
Choosing the right rootstock is vital to ensure a successful harvest since the parent vine, Vitis. vinifera does not provide adequate resistance against phylloxera Vastatrix, a deadly root infection caused by the aphid-like insect, Daktulosphaira vitifoliae (Fitch). Phylloxera weakens the vines causing root galls making it susceptible to fungal infections. It has plagued vineyards, decimating crops in California, and completely devastated vines planted on AXR1 type B rootstocks. It is estimated to have cost the industry $6 billion to uproot valuable mature vines and replant with vines grafted onto sturdier rootstocks.
To overcome this disease, grapes are grown on rootstocks from a variety of Vitis species selected from native areas or hybrids that use native species to form new rootstocks. The most commonly used are Vitis rupestris, V. riparia, V. berlandieri, and V. champinii. A grafted vine consists of the scion which is seen above ground and the rootstock which provides the root system and lower trunk joined at the graft union (protected with wax like above).
Image by Wine Folly
Pruning is an artform and traditional viticulture techniques require patience and skill passed down through generations. Below are a few training techniques used in viticulture but you can learn more by following Dan from apicaltexas with great videos on pruning techniques in the field.
Developing the vineyard should factor the best rootstock suited for particular environmental conditions. Soil type, pest resistance, tolerance to drought, wetness, salinity, and lime must all be considered when siting a vineyard.
Most experts suggest loamy soil as the best type of soil for grape growing. A crumbly mix of sand, silt, and clay when blended with other soils in the right amounts offers the ideal soil type. This is because the clay in loam drains well but also contains moderate amounts of water and nutrients within the preferred pH range (pH 6.5-6.8). Sonoma and Napa Valley are both loam soil regions.
Even though grapevines are considered relatively tolerant to water deficits, growth and yield can be reduced in drought-like conditions. Drought tolerant rootstocks enable the scion to grow and yield even when water supplies are limited, a desirable trait if irrigation is likely to cause waterlogging in heavy clay soil. Acidic soils are common in many viticultural growing regions, and liming is common-practice to increase soil pH. The salinity of irrigation water and rising water tables can also affect productivity in grapevines which can have a detrimental effect on wine quality.
Rootstocks can have a pronounced influence on the mineral nutrition of the fruiting variety. Vigorous vines can deplete zinc levels while increasing the uptake of potassium with regular soil analysis crucial to produce the best fruit.
While growing under cover may not suit large scale vineyards, certainly the early stages can be started off under greenhouse control much like blueberries. A drip irrigation system will work well to ensure a good source of minerals is available at the root base with free drainage.
If you are planning to grow in containers, a half barrel size is more than adequate with a light multipurpose compost. There’s no doubt selection of soil can be tricky because the soil type needs to work for both the vine and the rootstock. Remember sandy soil seems to have an advantage in resistance to phylloxera.
Microclimates & Disease Prevention
Year one begins with training the cordon or guyot from the rootstock to produce two dominant shoots. Year two and the tendrils will form without fruiting but it is not until year three that fruit trusses will become visible on most vines. These can then be trained as desired with supports. How vigorous the growth develops will hugely depend on whether it’s grown as scions or as dominant root stocks.
Mildew, powdery (Erisyphe necator) and downy (Plasmopara viticola) mildew are the predominant diseases encountered in viticulture. These favor successive periods of hot and humid conditions. Suppression of grapevine powdery mildew is problematic with resistance built up to systemic fungicides. This can also lead to weakened vines and susceptibility to Botrytis (botrytis cinerea) another fungal disease which affects almost every part of the vine, usually caused by high humidity coupled with strong winds. Mitigation traditionally introduces better airflow through the truss and canopy, pinching out individual berries can assist, allowing for circulation to circumvent rot problems. New ideas using light treatments are being trialed at Cornell university and UV treatments applied once a week up to 200 J/m2 on Chardonnay vines have proven to reduce powdery and downy mildew conidia germination by almost 100% and 50% respectively.
Image sourced from David M. Gadoury, Cornell.
LEDs have also been shown to boost yields. RB light encourages leaf growth and fruit maturation but little experimentation has been possible due to field positioning of grapes. Perhaps in the future we will see these autonomous tractors lighting up fields at night.
The French prevent early bud loss by using fire candles between vines. It’s a risky business balancing crop loss from frost with fire damage if not controlled. Water sprays are often employed to protect against frost damage by forming ice crystals around the buds during cold weather.
Field light spectrum can assist fruit bud development
Improving knowledge of environmental triggers for bud burst in grapes can help to optimize plant productivity, especially in marginal climates. In particular, an improved knowledge of the physiology of bud burst is fundamental to enable better crop management.
The point where a quiescent axillary bud commences regrowth is governed by both metabolic and signaling functions, driven by light, energy, and oxygen availability. Several grapevine studies have investigated the influence of low-intensity light on shoot physiology, suggesting that it is adapted to a low-light environment. Removing the apex can result in axillary bud outgrowth, as can changes in light intensity and quality. Axillary bud outgrowth is regulated by signals from the apex, which contain several light quality and quantity sensing pigments. These phytochromes sense red and far-red light, while cryptochromes and phototropins are involved in the perception of blue light. Accumulating evidence supports the function of photoreceptors in blue light perception resulting in activation of photomorphogenic gene expression, stimulating bud outgrowth.
Field trials with inter-canopy LED lights in California. Reach out if you need advice, we are here to help.
These photoreceptors regulate the expression of different transcription factors to coordinate light-dependent photomorphogenesis.
An early indicator of the transition to bud burst is ‘sap-flow’ preceded by an increase in xylem pressure leading the an increase in auxin and sugars in the sap.
Applying light theory helps improve knowledge of the physiology of bud burst which is fundamental to better canopy and crop forecasting, as the timing and coordination of this event will influence flowering, fruitset, and ripening.
Indoor low intensity RB LED lights – in Scotland year 2 with no trusses but plenty of tendrils and good vine growth.
Leafhoppers, cochylis and Lobesia botrana are dreaded pests that cause considerable damage to grape crops. IPM plays an important role in scouting for early damage to prevent disease. Prevention by spraying crops with regulated fungicides helps limit damage.
Micropropagation of new grape varieties
Fungal and viral infections have plagued vineyards particularly in California where in the 1980s the deadly root infection phylloxera returned, completely devastating vines planted on AXR1 rootstocks.
Viruses reduce plant vigor and delay bud break, and can be transmitted through vegetative propagation. Rapid micropropagation techniques can produce clean, disease-free, and vigorous plant material in a shorter time period, compared to conventional propagation techniques.
There are many reasons why breeding is important to the wine industry, and my friends at PCT wrote a neat article on why growing clean clones is one of the most efficient methods to scale grape plantlets.
New growth from a nodal cutting of my black Hamburg in initiation MS media growing under different low intensity LED spectrums.
A number of micropropagation techniques can be employed to clone grapes. Meristem culture induced from nodal cuttings can help to eliminate endophytes and produce virus free clones like above.
Sweet seedless grapes like cotton candy are produced via embryogenesis. Others like Selma Pete, a white grape, are grown for the raisin market. The power of breeding a particular variety for a select market can pay dividends.
Health properties of grapes
Health properties of grapes and grape juice are well documented particularly the black varieties which have higher anthocyanin levels, with known anti-inflammatory properties. Grape juice is a great way to boost immune systems and stay healthy. What we do know for sure is that resveratrol is well absorbed in the body and offers some exciting anticancer properties. Probably best to consume through black grape juice if you are concerned about the alcohol content in wine.
Turning grapes into wine
‘The older the vine the better the wine’ is a common saying in the industry, meaning the skin to pulp ratio increases creating a more intense flavor. Vines can be anywhere from 20 years to 120 years old and still produce good quality fruit. Some growers also believe older vines with deep root systems are more efficient at transferring minerals.
One thing’s for sure, there’s more science in wine making than you can shake a stick at! It’s chemistry without cooking. Even for hobbyists it’s a great pastime and relatively cheap to get started. As a student I was taught how to make wine in demijohns, it was a relatively simple process. Yeast varieties can also have a significant effect on alcohol production. My final year degree project was to establish the budding rate of Saccharomyces cerevisiae, the most common species of yeast in winemaking. Ah, that stirred tank fermenter with all those sensors, part biology, part engineering…..
Begin with good quality grapes and crush and press down hard until the bunches are smashed and the juice is released. For reds, ferment the juice, skins and seeds after removing stems.
At least 5 gallons of white grape juice can make five gallons of wine. Pour the juice into a demijohn. White grape juice is green to start and as it oxidizes it will turn a brown color during fermentation. Add wine yeast at a comfortable room temperature. It will foam as it releases carbon dioxide within a day or two, which signals the start of the process. Use an airlock to keep oxygen out and allow the carbon dioxide produced by to escape.
Red ‘must’ can be fermented in a large open container with just a towel, add wine yeast, and give it a good stir. It may begin to ferment in as little as 12 hours.
Red wines need to be stirred, at least twice per day when fermentation is going strong. You’ll see skin floating on the surface but just stir down regularly. Red wine should be around 80°F during fermentation. Test the sugar levels of the fermenting juice periodically with a basic hydrometer. It’s measured in degrees Brix, which equals sugar percentage will reduce to -2 Brix once fermentation is complete.
When the wine tastes like something you’d enjoy drinking, it’s time to bottle. Most white wines should mature after four to nine months whereas reds may take from six months to a year. You can learn more about winemaking from a course at Cornell or perhaps the ‘personality’ of wine from Jancis Robinson, an influential wine critic. Wine will benefit from a few weeks or months aging in the bottle, but who can wait that long?
My top reds are Spanish and Italian and I’m partial to a Californian rose. Chris would not say no to anything from the Napa Valley. Slàinte Mhath.
Janet Colston PhD is pharmacologist with an interest in growing ‘functional’ foods that have additional phytonutrients and display medicinal qualities that are beneficial to human health. She grows these using a range of techniques including plant tissue micropropagation and controlled environmental agriculture to ensure the highest quality control.
Unless otherwise stated all images are courtesy of The Functional Plant Company and property of Urban Ag News.