Grapes

Vitis vinifera

Origin:

The type genus for the grape family, Vitis is composed of more than 60 species of woody deciduous vines predominantly from the northern hemisphere. Vitis vinifera is by far the most important fruiting species in the genus worldwide and the one almost universally grown in Australia. It is predominantly from the Mediterranean region, central Europe and south west Asia.  Cultivation of grapes dates back to at least 4000BC. More than 70MT pa are produced worldwide, making them one of the most extensively cultivated fruit crops. The first grapevine planting material arrived in Australia with white settlement in 1788.

Climate:

Grapes are warm temperate zone plants, cultivated primarily within latitudes 34-49 degrees; however this range can be extended with special cultivar selection and management techniques.  Most commonly they are grown where temperatures for the mean warmest and coldest months are 18°C and -1°C respectively.  Extremes of long cold winters or very moist humid conditions in summer are detrimental to growth and yield.  In general, grapes need 150 – 180 frost-free days with temperatures above 10°C to grow, flower and set fruit.  In the dormant state they can withstand -20°C.  V. labrusca and its hybrids with V. vinifera are better suited to more tropical humid climates with wet summers.

Plant Description:

Grapes are indeterminate, woody vines with flaky bark, strong tendrils and canes that can be more than 30m long if unpruned.  Cultivated varieties are extensively pruned with little resemblance to wild or unmanaged plants.  In temperate areas they are normally deciduous. There is an extensive root system, including to depths of 5m, which facilitates good uptake of water and nutrients.  Leaves are alternate, lobed or not and 20-25cm wide.  In each axil there is an over-wintering lateral bud complex.  The leaf-opposed central primary bud normally grows in spring and produces a shoot with 2 lateral inflorescences.  Tendrils derive from these same precursor structures.  Plants are usually hardy and long-lived.

Relatives:

Vitaceae Family. There are 60-80 species in the genus, with V. labrusca and the muscadine species being relatively minor crops. Virginia creeper is an ornamental one, as are the majority of the rest.

Soils:

Not demanding provided there is good drainage.  Preference is pH 6-6.5 in light soils; if too fertile, undue vegetative rather than reproductive growth results.

Propagation:

Primarily by dormant cuttings that root very easily.  Grafting is used where particular features are sought, such as calcareous soil adaptation, nematode resistance or precocity.  Rootstocks other than vinifera are used where phylloxera (an aphid) infestation is established.

Cultivars:

There are many table grape varieties grown in Australia, with and without seeds.  Examples are: early season (Dec-Jan) Cardinal and Flame Seedless; mid (Feb-Mar) Maroo Seedless, Muscat and Red Globe; and late (Mar-May) Crimson Seedless.  The early season cvs have reduced Medfly problems.

Flowering and Pollination:

Inflorescences are panicles located at the node opposite each leaf, containing  60-1000 small (2-7mm) flowers.  Shoots can have 1-5 inflorescences.  The hermaphrodite flowers have rudimentary sepals, 5 petals fused into a cap, 5 stamens and a pistil with a superior ovary containing 2 carpels. Pollen is shed as the anthers ripen and is primarily transported by wind, though rarely more than 7 metres from the source.  All commercial grapes require pollination for fruit set and most need fertilization. Parthenocarpic varieties require the former but not the latter.  Common set is 25-75% but there may be considerable fruit drop soon after.  Seedlessness is popular in the market and is the result of parthenocarpy or stenospermocarpy.  Self-pollination following anthesis does not usually require a vector.  Warm conditions improve fruit set.

Cultivation:

Plant in full sun.  No fruit should be carried for the first 2 years while establishing a framework that normally consists of a single stem with permanent arms from which each year's crop will be produced.  Light fertilization with young plants will hasten development, but in the mature state care must be taken to guard against undue vegetative growth and consequent reduced flowering.  Deficiencies in P, K and Cu have been reported in WA coastal sands, and alkaline soils may require additional nutrient needs to be met.

Vines should have some sort of support as they climb by tendrils. They are best trained along wires or grown against and on top of fences. An elaborate system such as is used by vineyards is not necessary. Support is optional the first summer, but essential after that. However, another training system produces vines with thick, straight, free-standing trunks surmounted by a radial canopy of branches.

Wind Tolerance:

Good with normal trellis or pergola support in place.

Pruning:

If plants are being grown for table grapes then they'll need to be heavily pruned each year for best fruiting of large bunches and berries.  There are 2 main techniques, namely spur and cane pruning depending on the fruitful vigour of the variety, the former being more common than the latter.  For large bunches and berries, fruit thinning is also practiced. Pruning is best performed in late winter before buds along the branches begin to swell. Any and all twiggy growth growing from the main trunk or the main canes should be removed during this time period.

The key to grapevine pruning is having an understanding of the vine's fruiting habit. Grapes produce the most fruit on shoots growing off 1-year-old canes. If you have too many old canes (from no pruning), then fewer grapes are obtained. Conversely, if vines are pruned back completely each year, then lots of new growth, but few grapes are obtained. For many varieties, renewal pruning is practiced: the vine is shaped to have 2 main arms. Each year in rotation, one arm is removed back to the first 2 buds.

Different varieties have the flower buds at different position along the canes. You must know which nodes will have the flower buds. This decides pruning length.

The Fruit:

The fruit is a berry with 0-4 tan coloured seeds.  Skin colour and flesh ranges from pale green to red or deep purple-black.  Fresh, ripe table grapes contain up to 15% sugars, plus there are many phenolic compounds that contribute to flavour and have valuable antioxidant properties.

Fruit Production and Harvesting:

Commonly plants will fruit in the first 2-3 years after planting, with yield increasing over the next 2-3 seasons.  Fruit harvest may be 4-7 months after bloom.  It is critical to pick fruit at the right time to achieve the best balance of acidity, sugars and other volatiles for maximal flavour.  Fruit do not ripen further after harvest.  Table grapes are commonly harvested by hand whereas machine harvesting is more common for production of wine, dried fruit and juice.  Rain during the ripening period can cause fruit splitting. Often grapes have good size and colour one week before the sugar content is sufficiently high. After the sugar content has peaked, quality deteriorates rapidly. A hand-held refractometer provides a simple means of estimating the sugar content in grapes and other fruit.

Fruit Uses:

Most grapes are used in making wine, but table grapes can be eaten raw or they can be used for making juice, jelly, vinegar, grape seed extract, raisins, currants, sultanas, grape seed oil or fermented to produce wine. They can be stored for 3 or more months if kept at 1°C

Pests and Diseases:

Humidity increases disease load that may require regular attention and spraying.  Major pests in WA are mites, caterpillars, weevils, nematodes and birds, with the latter usually requiring bagging or netting of the bunches or vines respectively.The main diseases are powdery mildew, anthracnose and severe viral infections.

Comments:

Grapes grow very well in south west WA with our long hot dry summers.  Some management tasks will need to be addressed to get handsome loads of fresh fruit every year. A traditional siting for grape vines is a trellis built over a patio or footpath.

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