Grapes (Vitis spp)

How well established is this crop?

This crop has been grown commercially in the region for at least 20 years. Commercial returns, current growers and some level of regional based research is available to help those new to this industry.

Background

Grapes have started something of a new goldrush in Central Otago over the past 15 years. However, the first plantings of this crop occurred back in 1864 on the Monte Christo estate near Clyde. Not much came from this because of damage from rabbits and frosts. Interest in grapes was rekindled in the early 1970s when the DSIR made some trial plantings at Earnscluegh near Alexandra. Plantings began in the 1980's.

Although frosts can have a serious impact on yield, the environment imparts the wines from the region with some award winning characteristics. The low rainfall and soil type combined with the short intense summer sees the fruit ripen with intense flavours. The short season also means the vines cannot ripen a large number of bunches meaning quality not quantity is the aim of the Central Otago wine maker.

Climate

The key climatic requirement of a grape growing area is heat. This can be measured using a term called Growing Degree Days or GDD for short. A base temperature is always stated for a GDD figure. For grapes this is usually quoted at a base temperature of 10°C.

To grow grapes successfully you need to have an annual GDD figure of around 900 +. Any less than this and you will not be able to ripen grapes properly before the winter arrives.

Winter Chilling and Frosts

All areas of Otago have sufficient winter chilling to set fruit on a grapevine. The harsh winter frosts in Central Otago do not seem to affect the vine when dormant. This changes when the vines come into leaf and then flower and start producing small fruit.

The hard frosts of a Central Otago autumn and spring can have a serious impact on grapes. Spring frosts are the worst, because they kill the flowers and young grapes on the vines leaving no crop to harvest. In the autumn the frosts can strip the vines of leaves leaving no way for the fruit to ripen. If thinking of growing grapes investment in overhead irrigation to reduce the affect of this, or the use of a windmill is strongly recommended.

Rainfall and Irrigation

An ideal rainfall pattern for grapes would be around 1000mm per annum spaced evenly through the year. Unfortunately this does not happen in Central Otago with around 300-400mm per annum being the norm. Extra irrigation water is needed especially during the summer as the fruit begins to swell. Coastal Otago on the other hand, probably has too much rain and heavy use of fungicides would be needed to guarantee a crop. Also much of Otago does not have the heat accumumulation required (GDD's). Central Otago has some excellent sites.

Wind

The vines on the outside of blocks can be affected by turbulant winds, while those on the inside tend to be sheltered. Because of this some growers are now planting shelter when this has not been common practice in the past.

Soil

To produce a good quality wine it is advisable to grow vines in a free draining soil. However the overriding factor is the heat units in the area.

Fertility

Grapes require moderate levels of soil fertility. Regular soil and foliage tests will quickly identify a deficiencies and this can be easily corrected with the addition of fertiliser. Companies such as Hills Laboratories and Ravensdown have a datasheet with the recommended soil and leaf nutrient levels for this crop. See the ‘Contacts’ section at the end of this datasheet.

Weed Control

Weed control in vineyards tends to be quite straightforward. When vines are planted, plastic spray-guards are put around the trunks. This prevents rabbit damage and allows herbicides to be sprayed right up to them. Weeds growing up inside these guards are removed by hand. As the vine matures the bark on the trunk hardens and herbicides can be sprayed on them with no damage to the vine.

Varieties

Central Otago is known for its Pinot Noir grapes which account for over two thirds of all vines in the ground. Pinot Gris and Chardonnay are the next most popular varieties, followed by Riesling, Sauvignon Blanc and Gewurztraminer.

Pests and Diseases

The main threat to the Central Otago wine industry is the aphid like insect Phylloxera which arrived in the area in 2000. Until that time many of the vines were rooted cuttings which were susceptible. Since that time a major replanting program has been underway and now well over 60% of the vines in the area are growing on Phyloxera resistant rootstocks.

Other insect pests include wasps which eat into the grape bunches meaning they cannot be used to make wine.

Birds are another major problem with some studies showing losses of up to 50% of the grapes. Growers control birds by netting the vines and then shooting/scaring around the blocks.

Rabbits are the other vertebrate pest causing damage especially to young vines. Rabbit control using plastic spray guards around vines at planting followed up with aggressive shooting and netting blocks is recommended.

Powdery Mildew and Botrytis are the two main fungal diseases to affect grapes. Both of these can be controlled with fungicides.

Layout

Most blocks are planted with rows running north-south. This ensures the whole vine gets sunshine during the day. Row spacing is usually 2-3m and the distance between plants within a row is usually 1.2 - 1.8m.

The most common post and wire system is a 3 wire Vertical Shoot Positioning (VSP) system with posts 1.8m tall. The fruiting wire is 90cm from the ground, with two sets of tuck wires positioned at 1.3m and 1.7m.

General Management

After the posts and wires are established in the block and the young vines are planted, weed control, training and irrigation take up the majority of time in the first season. Training the vine up onto the wires is required with seasonal pruning as grapes flower and fruit on current seasons growth. As the crop starts being produced, leaf plucking is needed to allow light onto grape bunches. Fungal control is also required over this time to ensure the crop is not lost.

Harvest

Most Central Otago growers use hand harvesting methods to get the crop in because the blocks are very small. It also means a better quality product for the wine maker to start with. As the industry gets larger and less labour is available, machine harvesting is expected to be more common.

Equipment

Small blocks are best managed with a small tractor unit for spraying and grass mowing etc. Pruning needs secauters and ties. Labour is the main requirement.

Returns

Expected grape yields in Central Otago are lower than the rest of New Zealand due to the more extreme climate. In years 1 and 2 no fruit will be produced. This potentially increases to 1t/ha in year 3; and increasing to approximately 6t/ha in the years afterwards. Returns depend on variety.

Contacts

If you are thinking of growing grapes in Otago contact the Central Otago grape Grower Association.

http://www.otagowine.com

For fertility information
http://www.hortnet.co.nz/publications/guides/fertmanual/grapes.htm